Polarization Resolved Raman Spectroscopy Reveals Excitonic Plasma Pairing Glue in the Iron Pnictide Superconductors

by Tommy on 24/10/2014


Critical Charge Fluctuations in Iron Pnictide Superconductors, V. K. Thorsmølle, M. Khodas, Z. P. Yin, Chenglin Zhang, S. V. Carr, Pengcheng Dai and G. Blumberg

The multiband nature of iron pnictides gives rise to a rich temperature-doping phase diagram of competing orders and a plethora of collective phenomena. At low dopings, the tetragonal-to-orthorhombic structural transition is closely followed by a concomitant spin density wave transition both being in close proximity to the superconducting phase. A key question is the microscopic mechanism of high-Tc superconductivity and its relation to orbital ordering and magnetism. Here we study the NaFe1−xCoxAs superconductor using polarization resolved Raman spectroscopy. The Raman susceptibility shows critical non-symmetric charge fluctuations across the entire phase diagram associated with a hidden ordered state. The charge fluctuations are interpreted in terms of plasma waves of quadrupole intra-orbital excitations in which the electron and hole Fermi surfaces breath in-phase. Below Tc, these plasmons undergo a metamorphosis into a coherent ingap mode of extraordinary strength and at the same time serve as a glue for non-conventional superconducting pairing.

This paper comes with a companion paper discussing some of the parent compounds.


On the origin of the electronic anisotropy in iron pnicitde superconductors, W.-L. Zhang, P. Richard, H. Ding, Athena S. Sefat, J. Gillett, Suchitra E. Sebastian, M. Khodas and G. Blumberg

We use polarization-resolved Raman spectroscopy to study the anisotropy of the electronic characteristics of the iron-pnictide parent compounds AFe2As2 (A = Eu, Sr). We demonstrate that above the structural phase transition at Ts the dynamical anisotropic properties of the 122 compounds are governed by the emergence of xy-symmetry critical collective mode foretelling a condensation into a state with spontaneously broken four-fold symmetry at a temperature T*. However, the mode’s critical slowing down is intervened by a structural transition at Ts, about 80 K above T*, resulting in an anisotropic density wave state.

Well this is going to throw a wrench is some people’s gears. Mechanisms schmeckanisms.

As Mr. Spock would say – fascinating.

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Subvalent Monocation Bismuth Bi+ NIR Luminescence Centers

by Tommy on 23/10/2014
Subvalent Bismuth Monohalide Excited States

Subvalent Bismuth Monohalide Excited States


Centers of near-infrared luminescence in bismuth-doped TlCl and CsI crystals, V.O. Sokolov, V.G. Plotnichenko and E.M. Dianov, Optics Express 21, 9324-9332, (2013)

DOI: 10.1364/OE.21.009324


A comparative first-principles study of possible bismuth-related centers in TlCl and CsI crystals is performed and the results of computer modeling are compared with the experimental data. The calculated spectral properties of the bismuth centers suggest that the IR luminescence observed in TlCl:Bi is most likely caused by Bi+ — V-Cl centers (Bi+ ion in thallium site and a negatively charged chlorine vacancy in the nearest anion site). On the contrary, Bi+ substitutional ions and Bi2+ dimers are most likely responsible for the IR luminescence observed in CsI:Bi.

See also: http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-3-3-400

Influence of thermal treatment on the near-infrared broadband luminescence of Bi:CsI crystals, Xiao Fan, Liangbi Su, Guohao Ren, Xiantao Jiang, Haibo Xing, Jun Xu, Huili Tang, Hongjun Li, Lihe Zheng, Xiaobo Qian, and He Feng, Optical Materials Express, Vol. 3, Issue 3, pp. 400-406 (2013)

DOI: 10.1364/OME.3.000400

Near-infrared (NIR) emitting active centers can exist abundant in Bi:CsI crystal. In addition, Bi:CsI have the simplest crystal structure, body-centered cubic (BCC). In this paper, annealing and quenching treatments were carried out in detail to identify the nature of NIR emitting active centers in Bi:CsI crystals. The changes of absorption and emission spectra with increasing the thermal treatment temperature indicated that the two NIR emission bands at 1210 nm and 1580 nm were related to Bi+ and Bi2+, respectively. Besides, the assignments of absorption bands and the thermal behaviors of Bi3+, Bi2+, Bi+ and Bi2+ were discussed as well.

Bi:AgCl seems to be closer to ambient Bi+ ions where the neutral atom complex is unstable.


Near-IR luminescence in bismuth-doped AgCl crystals, V. G. Plotnichenko, D. V. Philippovskiy, V. O. Sokolov, V. F. Golovanov, G. V. Polyakova, I. S. Lisitsky and E. M. Dianov, Optics Letters 38, 2965-2968 (2013)

DOI: 10.1364/OL.38.002965


Experimental and computer-modeling studies of spectral properties of crystalline AgCl doped with metal bismuth or bismuth chloride are performed. Broad near-IR luminescence band in the 0.8-1.2 μm range with time dependence described by two exponential components corresponding to the lifetimes of 1.5 and 10.3 μs is excited mainly by 0.39–0.44 μm radiation. Computer modeling of probable Bi-related centers in AgCl lattice is performed. On the basis of experimental and calculation data a conclusion is drawn that the IR luminescence can be caused by Bi+ ion centers substituted for Ag+ ions.

So Bi1+ exists in the solid state. That much is for sure. That’s half the battle.

Now I just need to get rid of that pesky cesium, lol.

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Ultracold Boson Fermion Thermoelectric Simulator Modeled

by Tommy on 23/10/2014
Ultra Cold Atomic Gas Boson Fermion Thermoelectric Simulator

Ultra Cold Atomic Gas Boson Fermion Thermoelectric Simulator


Violation of the Wiedemann-Franz Law for ultracold atomic gases, Michele Filippone, Frank Hekking and Anna Minguzzi,

We study energy and particle transport for one-dimensional strongly interacting bosons through a single channel connecting two atomic reservoirs. We show the emergence of particle- and energy – current separation, leading to the violation of the Wiedemann-Franz law. As a consequence, we predict different time scales for the equilibration of temperature and particle imbalances between the reservoirs. Going beyond the linear spectrum approximation, we show the emergence of thermoelectric effects, which could be controlled by either tuning interactions or the temperature. Our results describe in a unified picture fermions in condensed matter devices and bosons in ultracold atom setups. We conclude discussing the effects of a controllable disorder.

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N-Diamond Water Optical Carbon Onion Synthesis Pathway

by Tommy on 20/10/2014


A new phase transformation path from nanodiamond to new-diamond via an intermediate carbon onion, J. Xiao, J.L. Li, P. Liu and G.W. Yang, Nanoscale (13 October 2014)

DOI: 10.1039/C4NR05246C

The investigation of carbon allotropes such as graphite, diamond, fullerenes, nanotubes and carbon onion and mechanisms that underlie their mutual phase transformation is a long-standing problem of great fundamental importance. New diamond (n-diamond) is a novel metastable phase of carbon with a face-centered cubic structure, being called “new diamond” because many reflections in its electron diffraction pattern are similar to those of diamond. However, producing n-diamond from raw carbon materials has been so far challenging due to n-diamond’s higher formation energy than that of diamond. Here, we, for the first time, demonstrate a new phase transformation path from nanodiamond to n-diamond via an intermediate carbon onion in the unique process of laser ablation in water, and establish that water plays a crucial role in the formation of n-diamond. When laser irradiates colloidal suspensions of nanodiamonds at ambient pressure and room temperature, nanodiamonds are firstly transformed into carbon onions serving as an intermediate phase, and sequentially carbon onions are transformed into n-diamonds driven by the laser-induced high-temperature and high-pressure from the carbon onion as a nanoscaled temperature and pressure cell upon the process of laser irradiation in liquid. This phase transformation not only gains a new insight into the physical mechanism involved, but also offers one suitable opportunity for breaking controllable pathways between n-diamond and carbon allotropes such as diamond and carbon onion.

Well gosh. There it is!

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Electrostatic and Thermal Control of Molecular Junctions Tested

by Tommy on 18/10/2014
Molecular Junction ZT Enhancement

Molecular Junction ZT Enhancement


Electrostatic control of thermoelectricity in molecular junctions, Youngsang Kim, Wonho Jeong, Kyeongtae Kim, Woochul Lee and Pramod Reddy, Nature Nanotechnology (5 October 2014)

doi: 10.1038/nnano.2014.209

Molecular junctions hold significant promise for efficient and high-power-output thermoelectric energy conversion. Recent experiments have probed the thermoelectric properties of molecular junctions. However, electrostatic control of thermoelectric properties via a gate electrode has not been possible due to technical challenges in creating temperature differentials in three-terminal devices. Here, we show that extremely large temperature gradients (exceeding 1 × 109 K m−1) can be established in nanoscale gaps bridged by molecules, while simultaneously controlling their electronic structure via a gate electrode. Using this platform, we study prototypical Au–biphenyl-4,4′-dithiol–Au and Au–fullerene–Au junctions to demonstrate that the Seebeck coefficient and the electrical conductance of molecular junctions can be simultaneously increased by electrostatic control. Moreover, from our studies of fullerene junctions, we show that thermoelectric properties can be significantly enhanced when the dominant transport orbital is located close to the chemical potential (Fermi level) of the electrodes. These results illustrate the intimate relationship between the thermoelectric properties and charge transmission characteristics of molecular junctions and should enable systematic exploration of the recent computational predictions that promise extremely efficient thermoelectric energy conversion in molecular junctions.

See also : http://arxiv.org/abs/1106.5208

Thermoelectric transport with electron-phonon coupling and electron-electron interaction in molecular junctions, Jie Ren, Jian-Xin Zhu, James E. Gubernatis, Chen Wang and Baowen Li, Phys. Rev. B, 85, 155443 (23 April 2012)

DOI: 10.1103/PhysRevB.85.155443


Within the framework of nonequilibrium Green’s functions, we investigate the thermoelectric transport in a single molecular junction with electron-phonon and electron-electron interactions. By transforming into a displaced phonon basis, we are able to deal with these interactions nonperturbatively. Then, by invoking the weak tunneling limit, we are able to calculate the thermoelectricity. Results show that at low temperatures, resonances of the thermoelectric figure of merit, ZT, occur around the sides of resonances of electronic conductance but drop dramatically to zero at exactly these resonant points. We find ZT can be enhanced by increasing electron-phonon coupling and Coulomb repulsion, and an optimal enhancement is obtained when these two interactions are competing. Our results indicate a great potential for single molecular junctions as good thermoelectric devices over a wide range of temperatures.

Eggimuffin. Yeah.

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Global Sea Level Over 35,000 Years Now Definitively Resolved

by Tommy on 18/10/2014
Global Sea Level 35K

Global Sea Level 35K


Sea level and global ice volumes from the Last Glacial Maximum to the Holocene, Kurt Lambeck, Hélène Rouby, Anthony Purcell, Yiying Sun and Malcolm Sambridge, Proceeding of the National Academies of Science of the United States of America, PNAS (13 October 2014)

doi: 10.1073/pnas.1411762111

Several areas of earth science require knowledge of the fluctuations in sea level and ice volume through glacial cycles. These include understanding past ice sheets and providing boundary conditions for paleoclimate models, calibrating marine-sediment isotopic records, and providing the background signal for evaluating anthropogenic contributions to sea level. From ∼1,000 observations of sea level, allowing for isostatic and tectonic contributions, we have quantified the rise and fall in global ocean and ice volumes for the past 35,000 years. Of particular note is that during the ∼6,000 y up to the start of the recent rise ∼100−150 y ago, there is no evidence for global oscillations in sea level on time scales exceeding ∼200 y duration or 15−20 cm amplitude.

The major cause of sea-level change during ice ages is the exchange of water between ice and ocean and the planet’s dynamic response to the changing surface load. Inversion of ∼1,000 observations for the past 35,000 y from localities far from former ice margins has provided new constraints on the fluctuation of ice volume in this interval. Key results are: (i) a rapid final fall in global sea level of ∼40 m in <2,000 y at the onset of the glacial maximum ∼30,000 y before present (30 ka BP); (ii) a slow fall to −134 m from 29 to 21 ka BP with a maximum grounded ice volume of ∼52 × 106 km3 greater than today; (iii) after an initial short duration rapid rise and a short interval of near-constant sea level, the main phase of deglaciation occurred from ∼16.5 ka BP to ∼8.2 ka BP at an average rate of rise of 12 m⋅ka−1 punctuated by periods of greater, particularly at 14.5–14.0 ka BP at ≥40 mm⋅y−1 (MWP-1A), and lesser, from 12.5 to 11.5 ka BP (Younger Dryas), rates; (iv) no evidence for a global MWP-1B event at ∼11.3 ka BP; and (v) a progressive decrease in the rate of rise from 8.2 ka to ∼2.5 ka BP, after which ocean volumes remained nearly constant until the renewed sea-level rise at 100–150 y ago, with no evidence of oscillations exceeding ∼15–20 cm in time intervals ≥200 y from 6 to 0.15 ka BP.

Finally! One less thing to worry about.

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Huge Thermopower by Superconductor Electron Hole Imbalance

by Tommy on 17/10/2014


Giant thermopower in superconducting heterostructures with spin-active interfaces, Mikhail S. Kalenkov and Andrei D. Zaikin (15 October 2014)

We predict parametrically strong enhancement of the thermoelectric effect in metallic bilayers consisting of two superconductors separated by a spin-active interface. The physical mechanism for such an enhancement is directly related to electron-hole imbalance generated by spin-sensitive quasiparticle scattering at the interface between superconducting layers. We explicitly evaluate the thermoelectric currents flowing in the system and demonstrate that they can reach maximum values comparable to the critical ones for superconductors under consideration.

See also: http://arxiv.org/abs/1405.3858

Electron-hole imbalance and large thermoelectric effect in superconducting hybrids with spin-active interfaces, Mikhail S. Kalenkov and Andrei D. Zaikin, Phys. Rev. B, 90, 134502 (1 October 2014)

DOI: 10.1103/PhysRevB.90.134502

We argue that spin-sensitive quasiparticle scattering may generate electron-hole imbalance in superconducting structures, such as, e.g., superconducting-normal hybrids with spin-active interfaces. We elucidate a transparent physical mechanism for this effect demonstrating that scattering rates for electrons and holes at such interfaces differ from each other. Explicitly evaluating the wave functions of electron-like and hole-like excitations in superconducting-normal bilayers we derive a general expression for the thermoelectric current and show that — in the presence of electron-hole imbalance — this current can reach maximum values as high as the critical current of a superconductor.


Finally something that has some real teeth to it.

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Photoinduced Insulator Metal Transition in Vanadium Dioxide

by Tommy on 17/10/2014


Instantaneous band gap collapse in photoexcited monoclinic VO2 due to photocarrier doping, Daniel Wegkamp, Marc Herzog, Lede Xian, Matteo Gatti, Pierluigi Cudazzo, Christina L. McGahan, Robert E. Marvel, Richard F. Haglund Jr., Angel Rubio, Martin Wolf and Julia Stähler

Using femtosecond time-resolved photoelectron spectroscopy we demonstrate that photoexcitation transforms monoclinic VO2 quasi-instantaneously into a metal. Thereby, we exclude an 80 femtosecond structural bottleneck for the photoinduced electronic phase transition of VO2. First-principles many-body perturbation theory calculations reveal a high sensitivity of the VO2 bandgap to variations of the dynamically screened Coulomb interaction, supporting a fully electronically driven isostructral insulator-to-metal transition. We thus conclude that the ultrafast band structure renormalization is caused by photoexcitation of carriers from localized V 3d valence states, strongly changing the screening before significant hot-carrier relaxation or ionic motion has occurred.

Behold the beginning of the Mottronics era.

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Bismuth Halide Monolayers as Quantum Spin Hall Insulators

by Tommy on 17/10/2014


Quantum Spin Hall Insulators of BiX/SbX (X = H, F, Cl, and Br) Monolayers with a Record Bulk Band Gap, Zhigang Song, Cheng-Cheng Liu, Jinbo Yang, Jingzhi Han, Meng Ye, Botao Fu, Yingchang Yang, Qian Niu, Jing Lu and Yugui Yao

Large bulk band gap is critical for the application of the quantum spin Hall (QSH) insulator or two dimensional (2D) Z2 topological insulator (TI) in spintronic device operating at room temperature (RT). Based on the first-principles calculations, here we predict a group of 2D topological insulators BiX/SbX (X = H, F, Cl, and Br) with extraordinarily large bulk gaps from 0.32 to a record value of 1.08 eV. These giant-gaps are entirely due to the result of strong spin-orbit interaction being related to the px and py orbitals of the Bi/Sb atoms around the two valley K and K’ of honeycomb lattice, which is different significantly from the one consisted of pz orbital just like in graphene and silicene. The topological characteristic of BiX/SbX monolayers is confirmed by the calculated nontrivial Z2 index and an explicit construction of the low energy effective Hamiltonian in these systems. We show that the honeycomb structure of BiX remains stable even at a temperature of 600 K. These features make the giant-gap Tls BiX/SbX an ideal platform to realize many exotic phenomena and fabricate new quantum devices operating at RT.


Large-Gap Quantum Spin Hall Insulator in Single Layer Bismuth Monobromide Bi4Br4, Jin-Jian Zhou, Wanxiang Feng, Cheng-Cheng Liu, Shan Guan, and Yugui Yao, Nano Lett., 14 (8), pp 4767–4771 (24 July 2014)

DOI: 10.1021/nl501907g


Quantum spin Hall (QSH) insulators have gapless topological edge states inside the bulk band gap, which can serve as dissipationless spin current channels. The major challenge currently is to find suitable materials for this topological state. Here, we predict a new large-gap QSH insulator with bulk direct band gap of ∼0.18 eV, in single-layer Bi4Br4, which could be exfoliated from its three-dimensional bulk material due to the weakly bonded layered structure. The band gap of single-layer Bi4Br4 is tunable via strain engineering, and the QSH phase is robust against external strain. Moreover, because this material consists of special one-dimensional molecular chain as its basic building block, the single layer Bi4Br4 could be torn to ribbons with clean and atomically sharp edges. These nanoribbons, which have single-Dirac-cone edge states crossing the bulk band gap, are ideal wires for dissipationless transport. Our work thus provides a new promising material for experimental studies and practical applications of the QSH effect.



Low-Energy Effective Hamiltonian for Giant-Gap Quantum Spin Hall Insulators in Honeycomb X-Hydride/Halide (X=N-Bi) Monolayers, Cheng-Cheng Liu, Shan Guan, Zhigang Song, Shengyuan A. Yang, Jinbo Yang and Yugui Yao, Phys. Rev. B 90, 085431 (25 August 2014)

DOI: 10.1103/PhysRevB.90.085431

Using the tight-binding method in combination with first-principles calculations, we systematically derive a low-energy effective Hilbert subspace and Hamiltonian with spin-orbit coupling for two-dimensional hydrogenated and halogenated group-V monolayers. These materials are proposed to be giant-gap quantum spin Hall insulators with record huge bulk band gaps opened by the spin-orbit coupling at the Dirac points, e.g., from 0.74 to 1.08 eV in BiX (X = H, F, Cl, and Br) monolayers. We find that the low-energy Hilbert subspace mainly consists of px and py orbitals from the group-V elements, and the giant first-order effective intrinsic spin-orbit coupling is from the on-site spin-orbit interaction. These features are quite distinct from those of group-IV monolayers such as graphene and silicene. There, the relevant orbital is pz and the effective intrinsic spin-orbit coupling is from the next-nearest-neighbor spin-orbit interaction processes. These systems represent the first real 2D honeycomb lattice materials in which the low-energy physics is associated with px and py orbitals. A spinful lattice Hamiltonian with an on-site spin-orbit coupling term is also derived, which could facilitate further investigations of these intriguing topological materials.

Behold the beginning of the bismuth hydride iodide era. The iodobismuthine era. lol.

Better late than never. I kid you not.

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Lattice (Bi) Polarons Confirmed in Bismuthate Superconductors

by Tommy on 16/10/2014


Polaronic high-temperature superconductivity in optimally doped bismuthate Ba0.63K0.37BiO3, N. Derimow, J. Labry, A. Khodagulyan, J. Wang and Guo-meng Zhao

Magnetic measurements have been carried out in the superconducting and normal states of the optimally doped nonmagnetic bismuthate superconductor Ba0.63K0.37BiO3. The magnetic data along with previous muSR, resistivity, and tunneling data consistently show that there is a large polaronic enhancement in the density of states and effective electron-phonon coupling constant. The first-principle calculation within the density-functional theory indicates a small electron-phonon coupling constant of about 0.3-0.4, which can only lead to about 1 K superconductivity within the conventional phonon-mediated mechanism. Remarkably, the polaronic effect increases the electron-phonon coupling constant to about 1.4, which is large enough to leads to 32 K superconductivity. The present work thus uncovers the mystery of high-temperature superconductivity in bismuthate superconductors, which will also provide important insight into the pairing mechanism of other high-temperature superconductors.

See also: http://arxiv.org/abs/1206.3514

Model of the electron-phonon interaction and optical conductivity of Ba1−xKxBiO3 superconductors, R. Nourafkan, F. Marsiglio and G. Kotliar, Phys. Rev. Lett., 109, 017001 (2012)

DOI: 10.1103/PhysRevLett.109.017001

We investigate the physical properties of the Ba1−xKxBiO3 compounds with a focus on the optical properties. Results from the simple Holstein model, describing a single band coupled to an oxygen breathing mode with parameters derived from first principles calculations, are in excellent agreement with a broad range of experimental information. It accounts for an insulating parent compound at x = 0%, with a direct- (optical) and an indirect-gap, and a metal insulator transition around x = 0.38. Strong electron-phonon coupling leads to spectral weight redistribution over a frequency scale much larger than the characteristic phonon frequency and to strongly anharmonic phonons. We find that the metallic phase in the vicinity of phase boundary is close to the polaronic regime.

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Optical Probe Confirms Hubbard Model Charge Localization

by Tommy on 15/10/2014


Photo-enhanced antinodal conductivity in the pseudogap state of high-Tc cuprates, F. Cilento, S. Dal Conte, G. Coslovich, S. Peli, N. Nembrini, S. Mor, F. Banfi, G. Ferrini, H. Eisaki, M. K. Chan, C. J. Dorow, M. J. Veit, M. Greven, bD. van der Marel, R. Comin, A. Damascelli, L. Rettig, U. Bovensiepen, M. Capone, C. Giannetti and F. Parmigiani, Nature Communications, 5, 4353 (11 July 2014)

doi: 10.1038/ncomms5353

A major challenge in understanding the cuprate superconductors is to clarify the nature of the fundamental electronic correlations that lead to the pseudogap phenomenon. Here we use ultrashort light pulses to prepare a non-thermal distribution of excitations and capture novel properties that are hidden at equilibrium. Using a broadband (0.5–2 eV) probe, we are able to track the dynamics of the dielectric function and unveil an anomalous decrease in the scattering rate of the charge carriers in a pseudogap-like region of the temperature (T) and hole-doping (p) phase diagram. In this region, delimited by a well-defined TZ*neq(p) line, the photoexcitation process triggers the evolution of antinodal excitations from gapped (localized) to delocalized quasiparticles characterized by a longer lifetime. The novel concept of photo-enhanced antinodal conductivity is naturally explained within the single-band Hubbard model, in which the short-range Coulomb repulsion leads to a k-space differentiation between nodal quasiparticles and antinodal excitations.

This paper and the supplementary information is also open and downloadable.

And of course, I’ve already blogged that this has been tested with the parent insulator.


Witnessing the formation and relaxation of massive quasi-particles in a strongly correlated electron system, Fabio Novelli, Giulio De Filippis, Vittorio Cataudella, Martina Esposito, Ignacio Vergara Kausel, Federico Cilento, Enrico Sindici, Adriano Amaricci, Claudio Giannetti, Dharmalingam Prabhakaran, Simon Wall, Andrea Perucchi, Stefano Dal Conte, Giulio Cerullo, Massimo Capone, Andrey Mishchenko, Markus Grüninger, Naoto Nagaosa, Fulvio Parmigiani and Daniele Fausti

The non-equilibrium semiconductors physics is based on the paradigm that different degrees of freedom interact on different timescales. In this context the photo-excitation is often treated as an impulsive injection of electronic energy that is transferred to other degrees of freedom only at later times. Here, by studying the ultrafast particles dynamics in a archetypal strongly correlated charge-transfer insulator (La2CuO4), we show that the interaction between electrons and bosons manifest itself directly in the photo-excitation processes of a correlated material. With the aid of a general theoretical framework (Hubbard Holstein Hamiltonian), we reveal that sub-gap excitation pilots the formation of itinerant quasi-particles which are suddenly dressed (<100 fs) by an ultrafast reaction of the bosonic field.

Which was just published as:

Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system


Which is obviously now getting some press from Massimo’s press release, lol.

First they were massive, now they are just dressed.

All dressed up and no place to go.

The fat lady has finally sung.

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Doped Polyaniline – High zT Low Temperature Thermoelectric

by Tommy on 15/10/2014


High thermoelectric figure of merit in nanocrystalline polyaniline at low temperatures, Chandrani Nath, Ashok Kumar, Yung-Kang Kuo and Gunadhor Singh Okram, Appl. Phys. Lett. 105, 133108 (2014)


Thermoelectric coolers with figure of merit (ZT) close to unity at low temperatures are the need of the hour with new advances in high temperature superconductors, superconducting microelectronic circuits, quantum computers, and photonics. Here, we demonstrate that the conducting polymer polyaniline (PANI) doped with camphor sulfonic acid (CSA) synthesized in semi-crystalline nanostructures, possesses a giant Seebeck effect at low temperatures. The resulting enormously large Seebeck coefficient (up to 0.6 V/K) combined with an intrinsically low electrical conductivity and thermal conductivity give rise to a ZT = 0.77 at 45 K and ZT = 2.17 at 17 K.

Liquid Hydrogen. There are many different aspects of this report that are worth investigating.

I am so unfamiliar with this I even spelled it wrong.


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Ice Sheet Meltwater Floods Indicated by Coastal Iceberg Scour

by Tommy on 14/10/2014
Sub Tropical Coastal Iceberg Scour

Sub Tropical Coastal Iceberg Scour


Subtropical iceberg scours and meltwater routing in the deglacial western North Atlantic, Jenna C. Hill and Alan Condron, Nature Geoscience (12 October 2014)


Abrupt centennial-to-millennial shifts in Northern Hemisphere climate during the last deglaciation are thought to have been triggered by the discharge of large volumes of meltwater and icebergs to the subpolar North Atlantic1. Here we show that meltwater and icebergs were also transported directly from the Laurentide ice margin to the subtropical North Atlantic in a narrow coastal current. We present high-resolution bathymetric data from south of Cape Hatteras showing numerous scours that we interpret as relict iceberg keel marks. This indicates that icebergs up to 300 m thick drifted to southern Florida (24.5° N). In simulations with an ocean circulation model, during deglaciation, fresh water and icebergs routinely reached as far south as 32.5° N, in a period of less than four months. The southernmost scours formed only during periods of high meltwater discharge from the Northern Hemisphere ice sheets. In the simulations, such extreme periods of meltwater release led to a reversal of the typically northward surface flow in the nearshore subtropical western North Atlantic. We therefore suggest that significant volumes of iceberg-laden meltwater routinely bypassed subpolar regions and spread across the subtropical North Atlantic.

Well I guess proglacial lake outburst floods out the St. Lawrence are back in the news.

So the question still remains …

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Atom-Probe Tomography and Nanodiamond Isotope Analysis

by Tommy on 13/10/2014
Meteoritic Nanodiamond Carbon Isotope Analysis

Meteoritic Nanodiamond Carbon Isotope Analysis


Microscopy Method Goes Deep, Atom-probe tomography reveals the 3-D positions of atoms inside hard-to-analyze materials, Mitch Jacoby, Chemical and Engineering News, Cover Story, Volume 92, Issue 41, pp. 11-14 (13 October 2014)

Philipp R. Heck, an assistant curator at Chicago’s Field Museum, together with a team of researchers from about 10 institutions, applied similar methods to determine the carbon-12 to carbon-13 ratio in meteoritic nanodiamonds. Samples, which the team embedded in platinum tips, came from the thoroughly studied Allende meteorite, a massive rock that predates the solar system and broke up over northern Mexico in 1969.

The team’s aim was to determine whether carbon’s isotope distribution in the nanodiamonds differs markedly from its distribution on Earth. Finding such a sample would suggest that the carbon was formed via a nucleosynthesis method different from the one that formed Earth’s carbon. Major differences in isotope abundances have been measured in other extraterrestrial material. So far, the nanodiamond study has not turned up obvious differences in carbon isotope distributions.

But it’s not “case closed” just yet. The analysis has proved difficult because it pushes APT’s detection limits. The nanodiamond study requires accurately counting and sorting very small numbers of atoms from approximately 3-nm-diameter particles and spotting a difference from the earthly 13C abundance, which is only 1.1%. The investigation has so far shown that APT is well suited to the cosmic science task, but larger data sets need to be generated.


Meteorit. Planet. Sci. 2014, DOI: 10.1111/maps.12265

Atom-probe analyses of nanodiamonds from Allende, Philipp R. Heck, Frank J. Stadermann, Dieter Isheim, Orlando Auciello, Tyrone L. Daulton, Andrew M. Davis, Jeffrey W. Elam, Christine Floss, Jon Hiller, David J. Larson, Josiah B. Lewis, Anil Mane, Michael J. Pellin, Michael R. Savina, David N. Seidman and Thomas Stephan. Meteoritics & Planetary Science, Volume 49, Issue 3, pages 453–467 (4 March 2014)

Atom-probe tomography (APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub-nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of 12C/13C ratios in individual diamond grains, solving the decades-old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected.


Meteoritic Nanodiamond Analysis by Atom-Probe Tomography, J. B. Lewis, D. Isheim, C. Floss, T. Daulton, D. N. Seidman, P. R. Heck, A. M. Davis, M. J. Pellin, M. R. Savina, J. Hiller, A. Mane, J. Elam, O. Auciello, T. Stephan, Microsc. Microanal. 20 (Suppl 3), 2014


New Atom-Probe Tomography Data and Improved Techniques for Meteoritic Nandiamond Analysis, J. B. Lewis, D. Isheim, C. Floss, T. L. Daulton, D. N. Seidman, 45th Lunar and Planetary Science Conference (2014)

These are the carbon isotope analyses that have not yet been done, and remain to be applied to the so called sedimentary nanodiamonds from the Younger Dryas boundary horizon sediments.

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Bismuth Iodide Based Candidates for Topological Insulators

by Tommy on 10/10/2014
Bismuth  Mono Iodide Sub Halide

Bismuth Mono Iodide Sub Halide


Bismuth-based candidates for topological insulators: Chemistry beyond Bi2Te3, Anna Isaeva, Bertold Rasche and Michael Ruck, Physica Status Solidi, Rapid Research Letters, Volume 7, Issue 1-2, Pages 39–49 (12 February 2013)

Special Issue: Topological Insulators – From Materials Design to Reality (Eds.: Claudia Felser, Shoucheng Zhang, Binghai Yan)

DOI: 10.1002/pssr.201206405

The present contribution considers chemical aspects relevant for established and candidate topological insulators (TIs) based on the element bismuth. We provide an overview of selected bismuth-containing compounds with topological protection, place them among structurally related compounds and, proceeding from the comparison, propose further families and guidelines for the search of new candidate TIs. Owing to the unique electronic properties and structural flexibility, bismuth demonstrates an overwhelming diversity of structural motifs, including low-dimensional ones. Bismuth acts both as an electron donor and acceptor interacting with other elements, thus initiating a refined interplay of electron delocalization and localization that results in a wide range of properties – from an insulator or a semiconductor to a metal or a semimetal. Due to the bonding abilities of Bi 6p-orbitals an isolated pure-bismuth layer is bound to be corrugated. Yet compounds exist with planar decorated honeycomb nets of bismuth and transition-metal atoms that allow for testing theoretical predictions that nets with such geometry could support a TI phase.

The enhanced article from Wiley is great.

It saved me a trip uptown, but it looks like I will have to be going up there anyways!

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The One Dimensional Polymer Subhalide Bismuth Iodide Bi4I4

by Tommy on 10/10/2014


Electronic structure, galvanomagnetic and magnetic properties of the bismuth subhalides Bi4I4 and Bi4Br4, T.G. Filatova, P.V. Gurin, L. Kloo, V.A. Kulbachinskii, A.N. Kuznetsov, V.G. Kytin, M. Lindsjo and B.A. Popovkin, Journal of Solid State Chemistry, Volume 180, Issue 3, March 2007, Pages 1103–1109

DOI: 10.1016/j.jssc.2007.01.010

Two bismuth-rich subhalides, Bi4Br4 and Bi4I4, featuring extended quasi one-dimensional metallic fragments in their structures, have been investigated. The gas-phase technique of crystal growth has been refined for obtaining large (up to 5 mm long) single crystals. Electronic structure calculations on three-dimensional structures of both compounds have been performed (DFT level, hybrid B3LYP functional), predicting a semiconducting behavior for both compounds, with an indication of possible directional anisotropy of electric conductivity. Galvanomagnetic (resistance, magnetoresistance, Hall effect, thermopower) and magnetic (temperature and field dependence of magnetization) properties have been measured experimentally. Both compounds are found to be diamagnetic, room-temperature semiconductors with n-type conductivity. While Bi4Br4 demonstrates a typical case of one dimensionality, the difference in magnetoresistivity between Bi4Br4 and Bi4I4 indicates some weak interactions between isolated bismuth metallic fragments within the bismuth substructures.

I have taken up the case for metastable Bi1+ in the solid state again for several reasons. The topological insulator people have taken this up with a vengeance, and because these guys here have developed a gas phase synthesis producing high quality single crystals that can serve as a feed stock for any potential experiments. Also both iodine and hydrogen adatoms have been proposed to produce bismuth thin films and monolayers on silicon, and double walled bismuth nanotubes have already been created using the Bi4I4 as the starting point. More on this later.

I see that Professor Popovkin has already passed away. Dikarev carries on.


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Thermoelectric Properties of Topological Insulators Investigated

by Tommy on 9/10/2014


Enhanced Thermoelectric Performance and Anomalous Seebeck Effects in Topological Insulators, Yong Xu, Zhongxue Gan and Shou-Cheng Zhang, Phys. Rev. Lett. 112, 226801 (2 June 2014)

DOI: 10.1103/PhysRevLett.112.226801

Improving the thermoelectric figure of merit zT is one of the greatest challenges in material science. Recent discovery of topological insulators (TIs) offers new promise in this prospect. In this work, we demonstrate theoretically that zT is strongly size dependent in TI, and the size parameter can be tuned to enhance zT to be significantly greater than 1. Furthermore, we show that the life time of the edge states in TI is strongly energy dependent, leading to large and anomalous Seebeck effects with an opposite sign to the Hall effect. These striking properties make TIs the promising material for thermoelectrics science and technology.

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Thermoelectric Properties of a Bismuth Monolayer Investigated

by Tommy on 9/10/2014
Bismuth Monolayer ZT

Bismuth Monolayer ZT


Thermoelectric Properties of a Monolayer Bismuth, Long Cheng, Huijun Liu, Xiaojian Tan, Jie Zhang, Jie Wei, Hongyan Lv, Jing Shi, and Xinfeng Tang, J. Phys. Chem. C, 2014, 118 (2), pp 904–910 (23 December 2013)

DOI: 10.1021/jp411383j

The structural and electronic properties of a two-dimensional monolayer bismuth are studied using density functional calculations. It is found that the monolayer forms a stable low-buckled hexagonal structure, which is reminiscent of silicene. The electronic transport properties of the monolayer bismuth are then evaluated by using Boltzmann theory with the relaxation time approximation. By fitting first-principles total energy calculations, a modified Morse potential is constructed, which is used to predicate the lattice thermal conductivity via equilibrium molecular dynamics simulations. The room temperature ZT value of a monolayer bismuth is estimated to be 2.1 and 2.4 for the n- and p-type doping, respectively. Moreover, the temperature dependence of ZT is investigated and a maximum value of 4.1 can be achieved at 500 K.

On the Nature of Bismuth (I) Iodide in the Solid State

T. L. Elifritz, Spec. Sci. Tech., 17, 85, 1994

Ok. I can live with that.

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Pressure Induced Insulator Metal Transition in Bismuth Triiodide

by Tommy on 9/10/2014


Pressure-induced structural changes and insulator-metal transition in layered bismuth triiodide, BiI3: a combined experimental and theoretical study, T. R. Devidas, N. V. Chandra Shekar, C. S. Sundar, P. Chithaiah, Y. A. Sorb, V. S. Bhadram, N. Chandrabhas, K. Pal, U. V. Waghmare and C. N. R. Rao, J. Phys.: Condens. Matter, 26, 275502 (9 July 2014)


Noting that BiI3 and the well-known topological insulator (TI) Bi2Se3 have the same high symmetry parent structures, and that it is desirable to find a wide-band gap TI, we determine here the effects of pressure on the structure, phonons and electronic properties of rhombohedral BiI3. We report a pressure-induced insulator-metal transition near 1.5 GPa, using high pressure electrical resistivity and Raman measurements. X-ray diffraction studies, as a function of pressure, reveal a structural peculiarity of the BiI3 crystal, with a drastic drop in c/a ratio at 1.5 GPa, and a structural phase transition from rhombohedral to monoclinic structure at 8.8 GPa. Interestingly, the metallic phase, at relatively low pressures, exhibits minimal resistivity at low temperatures, similar to that in Bi2Se3. We corroborate these findings with first-principles calculations and suggest that the drop in the resistivity of BiI3 in the 1–3 GPa range of pressure arises possibly from the appearance of an intermediate crystal phase with a lower band-gap and hexagonal crystal structure. Calculated Born effective charges reveal the presence of metallic states in the structural vicinity of rhombohedral BiI3. Changes in the topology of the electronic bands of BiI3 with pressure, and a sharp decrease in the c/a ratio below 2 GPa, are shown to give rise to changes in the slope of phonon frequencies near that pressure.

This is ok with me too. I endorse this result!

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Time Resolved ARPES Reveals Electron Boson Coupling

by Tommy on 9/10/2014


Ultrafast quenching of electron-boson interaction and superconducting gap in a cuprate superconductor, Wentao Zhang, C. Hwang, C. L. Smallwood, T. L. Miller, G. Affeldt, K. Kurashima, C. Jozwiak, H. Eisaki, T. Adachi, Y. Koike, D.-H. Lee and A. Lanzara

Ultrafast spectroscopy is an emerging technique with great promise in the study of quantum materials, as it makes it possible to track similarities and correlations that are not evident near equilibrium. Thus far, however, the way in which these processes modify the electron self-energy—a fundamental quantity describing many-body interactions in a material—has been little discussed. Here we use time- and angle-resolved photoemission to directly measure the self-energy’s ultrafast response to near-infrared photoexcitation in high-temperature cuprate superconductor. Below the superconductor’s critical temperature, ultrafast excitations trigger a synchronous decrease of electron self-energy and superconducting gap, culminating in a saturation in the weakening of electron-boson coupling when the superconducting gap is fully quenched. In contrast, electron-boson coupling is unresponsive to ultrafast excitations above the superconductor’s critical temperature and in the metallic state of a related material. These findings open a new pathway for studying transient self-energy and correlation effects in solids.


Nature Communications, 5, 4959 (15 September 2014) doi:10.1038/ncomms5959

In this technique they reverse the roles of the pump and probe in ultrafast optical spectroscopy. Here they pump with the near infrared and then probe with the near ultraviolet. Very clever that.

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Exotic Electronic States of the Bismuthates Probed by Theory

by Tommy on 6/10/2014


Topological nature and the multiple Dirac cones hidden in Bismuth high-Tc superconductors, Gang Li, Binghai Yan, Ronny Thomale and Werner Hanke

Recent theoretical studies employing density-functional theory have predicted BaBiO3 (when doped with electrons) and YBiO3 to become a topological insulator (TI) with a large topological gap (∼ 0.7 eV). This, together with the natural stability against surface oxidation, makes the Bismuth-Oxide family of special interest for possible applications in quantum information and spintronics. The central question, we study here, is whether the hole-doped Bismuth Oxides, i.e. Ba1−xKxBiO3 and BaPb1−xBixO3, which are “high-Tc” bulk superconducting near 30 K, additionally display in the further vicinity of their Fermi energy EF a topological gap with a Dirac-type of topological surface state. Our electronic structure calculations predict the K-doped family to emerge as a TI, with a topological gap above EF. Thus, these compounds can become superconductors with hole-doping and potential TIs with additional electron-doping. Furthermore, we predict the Bismuth-Oxide family to contain an additional Dirac cone below EF for further hole doping, which manifests these systems to be candidates for both electron- and hole-doped topological insulators.

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Cosmic Soup Smokers and the Origin of Life on the Planet Earth

by Tommy on 4/10/2014
Carbon Dioxide Fogger

Carbon Dioxide Fogger

Hat tip to PZ Myers on this. I don’t go over there much anymore because the commenters are uninformed and idiotic, but I just happened to stop in today for some reason, boredom probably, and I noticed that he linked to this highly informative blog post.


Which discusses this highly informational paper already a year and a half old.

Sousa, F.L., Thiergart, T., Landan, G., Nelson-Sathi, S., Pereira, I. A., Allen, J.F., Lane, N. and Martin, W.F. (2013) Early bioenergetic evolution. Philosophical Transactions of the Royal Society B: Biological Sciences 368:20130088. [doi: 10.1098/rstb.2013.0088]

Where you will discover that the paper and supplementary information are downloadable.

Life is the harnessing of chemical energy in such a way that the energy-harnessing device makes a copy of itself. This paper outlines an energetically feasible path from a particular inorganic setting for the origin of life to the first free-living cells. The sources of energy available to early organic synthesis, early evolving systems and early cells stand in the foreground, as do the possible mechanisms of their conversion into harnessable chemical energy for synthetic reactions. With regard to the possible temporal sequence of events, we focus on: (i) alkaline hydrothermal vents as the far-from-equilibrium setting, (ii) the Wood–Ljungdahl (acetyl-CoA) pathway as the route that could have underpinned carbon assimilation for these processes, (iii) biochemical divergence, within the naturally formed inorganic compartments at a hydrothermal mound, of geochemically confined replicating entities with a complexity below that of free-living prokaryotes, and (iv) acetogenesis and methanogenesis as the ancestral forms of carbon and energy metabolism in the first free-living ancestors of the eubacteria and archaebacteria, respectively. In terms of the main evolutionary transitions in early bioenergetic evolution, we focus on: (i) thioester-dependent substrate-level phosphorylations, (ii) harnessing of naturally existing proton gradients at the vent–ocean interface via the ATP synthase, (iii) harnessing of Na+ gradients generated by H+/Na+ antiporters, (iv) flavin-based bifurcation-dependent gradient generation, and finally (v) quinone-based (and Q-cycle-dependent) proton gradient generation. Of those five transitions, the first four are posited to have taken place at the vent. Ultimately, all of these bioenergetic processes depend, even today, upon CO2 reduction with low-potential ferredoxin (Fd), generated either chemosynthetically or photosynthetically, suggesting a reaction of the type ‘reduced iron → reduced carbon’ at the beginning of bioenergetic evolution.

The blog comments are highly informative as well. Not PZ’s, I would just avoid that place.

I like the distinction between metabolic energetics and informatics.

Happy Sputnik Day! Update: Happy Post Sputnik Day!

Update 2: Happy Pre Sputnik Day! lol. Anyways, after reading this paper and some of the referenced papers, and then after thinking about it and sleeping on it for a couple of days, I do have a few thoughts on the bigger picture here. First of all, on the transition from energetics to informatics, the proto replicators would start using the energy channels almost immediately, and the molecules and pathways that are able to store usable information about those energy exploiting mechanisms and pathways would be preferentially sustained in the encapsulated micro environments. As these smokers begin to spew out these biomolecules into the ocean a biological soup would begin to form in the region around the smokers, and then as encapsulated molecular replicators are discharged, those proto cells would inevitably decompose, creating an environment ever more enriched in biological soup over ever expanding regions around the smoking environment. There must have been a lot of alkaline smokers in the primordial sea.

Impacts of extraterrestrial carbonaceous material would be presumed to add raw materials to the soup, but the decomposition of free floating encapsulated molecular replicators from the smokers, no matter what their viability, would add more biomolecular fragments to the soup, rich in carbon based phosphorus and nitrogen compounds. Since the phosphorus is intimately involved in the energetics pathways, as more and more information based absorption and replication evolves, the phosphorus would be tightly recycled, and there would presumably be a lot of excess nitrogen. So the smoking based energy following pathways would evolve into information storing pathways, and then the ‘follow the energy’ strategy would evolve into a ‘use the information’ strategy to exploit new sources of energy and raw materials, which would be particularly useful for free floating proto replicators. And of course nitrogen is an unusually abundant and useful atom for storing and manipulating information. Thus we have reactivity (hydrogen and oxygen), structure (carbon), energetics (phosphorus) and informatics (nitrogen), and an abundance of metallic catalysts. Thus the smoker based paradigm would transition over time into the soup based paradigm, and then all is well in the world of smokers and soupers. With abundant sources and sinks of protons and electrons, in the form of alkali halide salts and alkaline earths, the perspective is complete. Just don’t add too much sulfur to the organic soup.

I’ll drink to that!

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Quantum Fluctuation Theory of Pseudogap Physics Presented

by Tommy on 30/09/2014


Pseudogap phenomena in ultracold atomic Fermi gases, Qijin Chen and Jibiao Wang, Phys. 9(5), 539-570 (2014)

The pairing and superfluid phenomena in a two-component ultracold atomic Fermi gas is an analogue of Cooper pairing and superconductivity in an electron system, in particular, the high Tc superconductors. Owing to the various tunable parameters that have been made accessible experimentally in recent years, atomic Fermi gases can be explored as a prototype or quantum simulator of superconductors. It is hoped that, utilizing such an analogy, the study of atomic Fermi gases may shed light to the mysteries of high Tc superconductivity. One obstacle to the ultimate understanding of high Tc superconductivity, from day one of its discovery, is the anomalous yet widespread pseudogap phenomena, for which a consensus is yet to be reached within the physics community, after over 27 years of intensive research efforts. In this article, we shall review the progress in the study of pseudogap phenomena in atomic Fermi gases in terms of both theoretical understanding and experimental observations. We show that there is strong, unambiguous evidence for the existence of a pseudogap in strongly interacting Fermi gases. In this context, we shall present a pairing fluctuation theory of the pseudogap physics and show that it is indeed a strong candidate theory for high Tc superconductivity.

This stunning review lays it all out in black and white for anybody who is still interested.

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Orbitronics Proposed for 1T-TaS2 Tantalum Disulfide

by Tommy on 26/09/2014


Orbital textures and charge density waves: towards orbitronics in transition metal dichalcogenides, T. Ritschel, J. Trinckauf, K. Koepernik, B. Büchner, M. v. Zimmermann, H. Berger, Y. I. Joe, P. Abbamonte and J. Geck

Low-dimensional electron systems, as realized naturally in graphene or created artificially at the interfaces of heterostructures, exhibit a variety of fascinating quantum phenomena with great prospects for future applications. Once electrons are confined to low dimensions, they also tend to spontaneously break the symmetry of the underlying nuclear lattice by forming so-called density waves; a state of matter that currently attracts enormous attention because of its relation to various unconventional electronic properties. In this study we reveal a remarkable and surprising feature of charge density waves (CDWs), namely their intimate relation to orbital order. For the prototypical material 1T-TaS2 we not only show that the CDW within the two-dimensional TaS2-layers involves previously unidentified orbital textures of great complexity. We also demonstrate that two metastable stackings of the orbitally ordered layers allow to manipulate salient features of the electronic structure. Indeed, these orbital effects enable to switch the properties of 1T-TaS2 nanostructures from metallic to semiconducting with technologically pertinent gaps of the order of 200 meV. This new type of orbitronics is especially relevant for the ongoing development of novel, miniaturized and ultra-fast devices based on layered transition metal dichalcogenides.

So now in addition to spintronics and magnonics, we also have orbitronics!

Shocking I tell you, shocking!

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Bismuth Iodide and Topological Insulators are in the News

by Tommy on 25/09/2014


Epitaxial growth of large-gap quantum spin Hall insulator on semiconductor surface, Miao Zhou, Wenmei Ming, Zheng Liu, Zhengfei Wang, Ping Li, and Feng Liu, Proceedings of the National Academies of Sciences of the United States of America, PNAS, 22 September 2014

DOI: 10.1073/pnas.1409701111

Quantum phase of matter is of great scientific and technological interest. The quantum spin Hall (QSH) insulator is a newly discovered two-dimensional material that exhibits topological edge state residing inside bulk energy gap, so that its edge is metallic with quantized conductance and its bulk is insulating. For its potential applications in spintronics and quantum computing, a large energy gap is desirable, e.g., for room-temperature application. So far, large-gap QSH insulators have been predicted only in freestanding films. Here we demonstrate the formation of a large-gap QSH state on a semiconductor substrate through epitaxial growth of heavy metal atoms on halogenated Si surface. Our findings not only reveal a new formation mechanism of large-gap QSH insulator, but may also pave the way for its experimental realization.

Formation of topological quantum phase on a conventional semiconductor surface is of both scientific and technological interest. Here, we demonstrate epitaxial growth of 2D topological insulator, i.e., quantum spin Hall state, on Si(111) surface with a large energy gap, based on first-principles calculations. We show that the Si(111) surface functionalized with one-third monolayer of halogen atoms [Si(111)-3√×3√-X (X = Cl, Br, I)] exhibiting a trigonal superstructure provides an ideal template for epitaxial growth of heavy metals, such as Bi, which self-assemble into a hexagonal lattice with high kinetic and thermodynamic stability. Most remarkably, the Bi overlayer is atomically bonded to but electronically decoupled from the underlying Si substrate, exhibiting isolated quantum spin Hall state with an energy gap as large as ∼0.8 eV. This surprising phenomenon originates from an intriguing substrate-orbital-filtering effect, which critically selects the orbital composition around the Fermi level, leading to different topological phases. In particular, the substrate-orbital-filtering effect converts the otherwise topologically trivial freestanding Bi lattice into a nontrivial phase; and the reverse is true for Au lattice. The underlying physical mechanism is generally applicable, opening a new and exciting avenue for exploration of large-gap topological surface/interface states.

Supplemental Supporting Information (PDF)

See also : http://arxiv.org/abs/1401.3392

Large-gap quantum spin Hall state on a semiconductor surface: The orbital filtering by substrate, Miao Zhou, Wenmei Ming, Zheng Liu, Zhengfei Wang, Yugui Yao, Feng Liu

For potential applications in spintronics and quantum computing, it is desirable to place a quantum spin Hall insulator [i.e., a 2D topological insulator (TI)] on a substrate while maintaining a large energy gap. Here, we demonstrate an approach to create the large gap 2D TI state on a semiconductor surface, based on extensive first principles calculations. We show that when Bi, Pb and Au atoms are deposited on a patterned H-Si(111) surface into a hexagonal lattice, both the Bi@H-Si(111) and Pb@H-Si(111) surfaces exhibit a 2D TI state with a large gap of {greater than} 0.5 eV while the Au@H-Si(111) surface is a trivial insulator. These interesting results are found to originate from the fact that the H-Si(111) surface acts as an atomic orbital filter to critically select the orbital composition around the Fermi level, resulting in different topological phases. In particular, the substrate orbital filtering effect converts the otherwise topologically trivial freestanding Bi and Pb lattices into a nontrivial phase; while the reverse is true for the Au lattice. The physical mechanism underlying this approach is generally applicable, opening up a new and exciting avenue for future design and fabrication of large-gap topological surface/interface states.

So, after almost exactly 20 years, it begins. Unfortunately, this story seems to have taken on a life of its own, reminiscent of the quantum computer in the Forbin Project. The way it sounds Google will have Colossus running on the barge next week, and we’ll have thinking and talking animatronic toys by Christmas. Such is life in the new university press release era of science.

On the Nature of Bismuth (I) Iodide in the Solid State, T. L. Elifritz, Spec. Sci. Tech., 17, 85, 1994

I doubt anyone remembers the 1995 Laboratory of the Year issue of R&D Magazine. Old news.

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High Temperature Superconductivity in the Cuprates

by Tommy on 18/09/2014
High Temperature Superconductivity in the Cuprates

High Temperature Superconductivity in the Cuprates


High Temperature Superconductivity in the Cuprates, B. Keimer, S. A. Kivelson, M. R. Norman, S. Uchida and J. Zaanen

The discovery of high temperature superconductivity in the cuprates in 1986 triggered a spectacular outpouring of creative and innovative scientific inquiry. Much has been learned over the ensuing 28 years about the novel forms of quantum matter that are exhibited in this strongly correlated electron system. This progress has been made possible by improvements in sample quality, coupled with the development and refinement of advanced experimental techniques. In part, avenues of inquiry have been motivated by theoretical developments, and in part new theoretical frameworks have been conceived to account for unanticipated experimental observations. An overall qualitative understanding of the nature of the superconducting state itself has been achieved, while profound unresolved issues have come into increasingly sharp focus concerning the astonishing complexity of the phase diagram, the unprecedented prominence of various forms of collective fluctuations, and the simplicity and insensitivity to material details of the “normal” state at elevated temperatures. New conceptual approaches, drawing from string theory, quantum information theory, and various numerically implemented approximate approaches to problems of strong correlations are being explored as ways to come to grips with this rich tableaux of interrelated phenomena.

This review should get you started and up to speed on recent developments.

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The Delta 9 Reusable Launch Vehicle

by Tommy on 27/08/2014


I have unretired briefly to do this for the United States Air Force (USAF).

The Delta 9 reusable launch vehicle concept consists essentially of a SpaceX Falcon 9R clone, implemented in hydrogen fuel, using recently developed and tested Blue Origin BE-3 engines.

The intent of such a program is to produce separate propulsion, airframe and operations sectors for the emerging commercial space flight industry in the same way our current airline industries are structured. This specific vehicle is designed in such a way as to motivate our legacy aerospace companies to begin participating substantively and competitively in this new commercial spaceflight industry, within their respective market niches and areas of expertise, while driving the industry forward with substantial Air Force funding, in much the same way that NASA has done with the COTS program, but focused more on specific Department of Defense space launch needs, with near term operational time frames (2018). The most obvious existing tank suitable for modification into the required launch vehicle would be the Boeing Delta IV Medium, but alternative airframe providers and technologies would not be ruled out.

So yeah, I’m a rocket scientist and a space architect. Now all I need is a rocket.


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