Graphene Nanodiamond Enthalpy of Formation and Phase Equilibrium Investigated

by Tommy on 31/07/2015

Enthalpy of formation of single and multilayer graphene, S. A. Gubin, I. V. Maklashova and E. I. Zakatilova, Russian Journal of Physical Chemistry A, 89, 8, 1434-1438 (August 2015)

An approximate equation of state of nanocarbon is used to estimate changes in the enthalpy of formation of single- and multilayer graphene and the graphene-nanodiamond phase equilibrium pressure as a function of geometrical shape, number of layers, and size of a graphene nanoparticle. It is found that upon an increase in the number of layers in graphene with particle sizes of 100–300 nm, the phase equilibrium pressure falls and tends to that of graphite-diamond equilibrium. An agreement between the estimations, the data from MD simulations of the graphene-nanodiamond phase equilibrium, and experimentally measured parameters of the graphene-nanodiamond phase transition was obtained.

The Russians know this stuff.

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Substitutional Superconductivity of Im3m Cubic H3S Phase

by Tommy on 31/07/2015

Possible Superconductivity Approaching Ice Point, Yanfeng Ge, Fan Zhang and Yugui Yao

Recently BCS superconductivity at 190 K has been discovery in a highly compressed hydrogen sulfide. We use first-principles calculations to systematically examine the effects of partially substituting the chalcogenide atoms on the superconductivity of hydrogen chalcogenides under high pressures. We find detailed trends of how the critical temperature changes with increasing the V-, VI- or VII-substitution rate, which highlight the key roles played by low atomic mass and by strong covalent metallicity. In particular, a possible record high critical temperature of 280 K is predicted in a stable H3S0.925P0.075 with the Im3m structure under 250 GPa.

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Bismuth Identified As Universal Ultra Broadband Photodetector

by Tommy on 30/07/2015

Ultra-broadband and high-responsive photodetectors based on bismuth film at room temperature, J. D. Yao, J. M. Shao and G. W. Yang, Scientific Reports, 5, 12320 (21 July 2015), doi:10.1038/srep12320

Bismuth (Bi) has undergone researches for dozens of years on account of its abundant physics including the remarkably high mobility, exceptional large positive magnetoresistance and the coexistence of an insulating interior as well as metallic surfaces. Very recently, two-dimensional topologically-protected surface states immune to nonmagnetic perturbation such as surface oxidation and impurity scattering were experimentally demonstrated through systematic magnetotransport measurements, e.g. weak antilocalization effect and angular dependent Shubnikov-de Haas oscillations. Such robust metallic surface states, which are efficient in carrier transportation, along with its small bulk gap (14 meV) make Bi favored for high-responsive broadband photodetection. Here, we for the first time demonstrate the stable ultra-broadband photoresponse from 370 nm to 1550 nm with good reproducibility at room temperature based on a Bi photodetector. The fabricated device’s responsivity approaches 250 mA/W, accompanied with a rise time of 0.9 s and a decay time of 1.9 s. The photocurrent is linear dependent on the voltage and incident power, offering good tunability for multi-purpose applications. Thickness-dependent conductance and photocurrent reveal that the bulk is the optically active layer while the surface channel is responsible for carrier transportation. These findings pave an avenue to develop ultra-broadband Bi photodetectors for the next-generation multifunctional optoelectronic devices.

Well whaddya know!

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Magnetic Field Driven Quantum Phase Transition Discovered in Weyl Semimental Tantalum Mono Phosphide TaP

by Tommy on 30/07/2015

Chenglong Zhang, Ziquan Lin, Cheng Guo, Su-Yang Xu, Chi-Cheng Lee, Hong Lu, Shin-Ming Huang, Guoqing Chang, Chuang-Han Hsu, Hsin Lin, Liang Li, Chi Zhang, Titus Neupert, M. Zahid Hasan, Junfeng Wang and Shuang Jia

Magnetic fields perturb the motion of charged quasi-particles in solids in different ways including driving a quantum phase transition to a new state. Well-known examples include the integer and fractional quantum Hall effects and the magnetic field-induced quantum phase transitions in topologically trivial semimetals such as graphite and bismuth. A Weyl semimetal provides the first-ever realization of Weyl fermions. Such an exotic metal is characterized by the topological charges, which are momentum space monopoles and anti-monopoles that arise from the distinct chiralities of the Weyl fermions. Here we report a new quantum phase transition that arises from the Weyl fermionic quasiparticles in the Weyl semimetal tantalum monophosphide, TaP, under an intense magnetic field. We observed a sharp sign reversal of the Hall resistivity when the Weyl fermions are confined to the lowest Landau level. In this exotic chiral electron subband of a Weyl semimetal, which was never been studied experimentally beforehand, the Weyl fermions form an unexpected, collective state whose contribution to the Hall signal suddenly vanishes at a critical magnetic field (H) where the Weyl fermions enter the lowest Landau level. Our results taken collectively represent the first magnetic-field-driven quantum phase transition in a 3D bulk topological material and may suggest the emergence of new topological phases due to electronic correlations.

Note: According to the records in Wuhan High Magnetic Field Lab, the first signature of condensation was observed in March 18, 2015.

Whoa! Heads up everybody.

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Existing Thermoelectrics Optimized For Electronic Microcooling

by Tommy on 30/07/2015

Performance and mass optimization of thermoelectric microcoolers, Yee Rui Koh, Kazuaki Yazawa and Ali Shakouri, International Journal of Thermal Sciences 97, 143–151 (November 2015)

We report a scalable and parametric analysis of thermoelectric (TE) microcoolers for hotspot cooling based on analytic formulations. Design for minimizing cooling power and least mass or cost of TE material is an ultimate goal for electronic devices that require spot cooling beyond that provided by passive heat transport to the thermal ground. Performance of thermoelectric hotspot cooling on electronic devices depends on external thermal resistances, physical dimension (thickness) of the thermoelectric element, and the applied drive current. Active cooling located at the hotspot minimizes the cooling power and the internal heat generation from the TE element and also minimizes the additional driving power used for heat rejection with a preexisting air-cooling fan or a liquid-cooling pump. Electronic devices are required to operate below a specific temperature for functionality and high reliability. The hotspot cooler must be designed to deal with the amount of heat generated from the heat source with this temperature constraint. We investigate two design cases: 1) the maximum cooling and 2) the minimum drive current for a given hotspot temperature to obtain an improved coefficient-of-performance (COP). The study explores the impact of individual thermoelectric material properties, i.e. Seebeck coefficient, electrical conductivity, and thermal conductivity to find the direction that should be taken with engineered materials. We show that COP up to 8 is possible for hotspot heat fluxes of about 80 W/cm2, if TE leg thickness is optimized to ∼ 20–30 microns with today’s Bi2Te3 material. Model shows that COP > 2–3 is possible for hotspot heat fluxes bigger than 200–300 W/cm2. We find that lowering the thermal conductivity have the greatest impact, resulting in a thinner element (and therefore lower cost) while maintaining the same figure-of-merit (ZT).

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Ceres Bright Crater Spots Actively Subliming Water Vapor Haze

by Tommy on 30/07/2015
Fifth Planet Ceres Topographic Map

Fifth Planet Ceres Topographic Map

Thunderbirds are go!

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Small Water Covered Life Bearing Terrestrial Planet Discovered

by Tommy on 20/07/2015
The Planet Earth - Third Rock From The Sun

The Planet Earth – Third Rock From The Sun

It’s called Terra by offworlders.

Earth by residents.

See also: The Sun – A Star Called Sol. The Moon – Luna.

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Discovery of a Weyl Fermion Semimetal Officially Announced

by Tommy on 19/07/2015

Princeton University Press Release

Discovery of a Weyl Fermion semimetal and topological Fermi arcs, Su-Yang Xu, Ilya Belopolski, Nasser Alidoust, Madhab Neupane, Guang Bian, Chenglong Zhang, Raman Sankar, Guoqing Chang, Zhujun Yuan, Chi-Cheng Lee, Shin-Ming Huang, Hao Zheng, Jie Ma, Daniel S. Sanchez, BaoKai Wang, Arun Bansil, Fangcheng Chou, Pavel P. Shibayev, Hsin Lin, Shuang Jia and M. Zahid Hasan, Science (16 July 2015), DOI: 10.1126/science.aaa9297

A Weyl semimetal is a crystal which hosts Weyl fermions as emergent quasiparticles and admits a topological classification that protects Fermi arc surface states on the boundary of a bulk sample. This unusual electronic structure has deep analogies with particle physics and leads to unique topological properties. We report the experimental discovery of a Weyl semimetal, TaAs. Using photoemission spectroscopy, we directly observe Fermi arcs on the surface, as well as the Weyl fermion cones and Weyl nodes in the bulk of TaAs single crystals. We find that Fermi arcs terminate on the Weyl nodes, consistent with their topological character. Our work opens the field for the experimental study of Weyl fermions in physics and materials science.

I had covered this earlier but now it’s official, I guess.

See also:

Experimental observation of Weyl points, Ling Lu, Zhiyu Wang, Dexin Ye, Lixin Ran, Liang Fu, John D. Joannopoulos and Marin Soljačić, Science (16 July 2015), DOI: 10.1126/science.aaa9273

The massless solutions to the Dirac equation are described by the so-called Weyl Hamiltonian. The Weyl equation requires a particle to have linear dispersion in all three dimensions (3D) while being doubly degenerate at a single momentum point. These Weyl points are topological monopoles of quantized Berry flux exhibiting numerous unusual properties. We performed angular-resolved microwave transmission measurements through a double-gyroid photonic crystal with inversion-breaking, where Weyl points have been theoretically predicted to occur. The excited bulk states show two linear dispersion bands touching at four isolated points in the 3D Brillouin zone, indicating the observation of Weyl points. This work paves a way to a variety of photonic topological phenomena in 3D.

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Two Dimensional Majorana Fermions Come in Two Flavors

by Tommy on 16/07/2015

Classification of Majorana Fermions in Two-Dimensional Topological Superconductors, Qiu-Bo Cheng, Jing He and Su-Peng Kou

Recently, Majorana Fermions (MFs) have attracted intensive attention due to their exotic statistics and possible applications in topological quantum computation (TQC). They are proposed to exist in various two-dimensional (2D) topological systems, such as px+ipy topological superconductor and nanowire-superconducting hybridization system. In this paper, two types of Majorana Fermions with different polygon sign rules are pointed out. A “smoking gun” numerical evidence to identify MF’s classification is presented through looking for the signature of a first order topological quantum phase transition. By using it, several 2D topological superconductors are studied.

Yum. I’ll take the left one.

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High Resolution ARPES Detects Cuprate Nodal Preformed Pairing State

by Tommy on 16/07/2015

Point nodes persisting far beyond Tc in Bi2212, Takeshi Kondo, W. Malaeb, Y. Ishida, T. Sasagawa, H. Sakamoto, Tsunehiro Takeuchi, T. Tohyama and S. Shin, Nature Communications 6, 7699 (9 July 2015), DOI: 10.1038/ncomms8699

In contrast to a complex feature of antinodal state, suffering from competing order(s), the “pure” pairing gap of cuprates is obtained in the nodal region, which therefore holds the key to the superconducting mechanism. One of the biggest question is whether the point nodal state as a hallmark of d-wave pairing collapses at Tc like the BCS-type superconductors, or it instead survives above Tc turning into the preformed pair state. A difficulty in this issue comes from the small magnitude of the nodal gap, which has been preventing experimentalists from solving it. Here we use a laser ARPES capable of ultrahigh energy resolution, and detect the point nodes surviving far beyond Tc in Bi2212. By tracking the temperature evolution of spectra, we reveal that the superconductivity occurs when the pair breaking rate is suppressed smaller than the single particle scattering rate on cooling, which governs the value of Tc in cuprates.

This results sets the maximum Tc of the quasi-2D cuprate family of superconductors.

Some people are not gonna like this.

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Happy Day After The Tenth Planet Pluto Day – July 15th, 2015

by Tommy on 15/07/2015
Charon - Moon of Pluto

Charon – Moon of Pluto

Plutoids – They’re everywhere.

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Electronic Structure of Weyl Semimetal Tantalum Phosphide TaP Mapped

by Tommy on 15/07/2015

Observation of Weyl nodes and Fermi arcs in TaP, N. Xu, H. M. Weng, B. Q. Lv, C. Matt, J. Park, F. Bisti, V. N. Strocov, D. gawryluk, E. Pomjakushina, K. Conder, N. C. Plumb, M. Radovic, G. Autès, O. V. Yazyev, Z. Fang, X. Dai, G. Aeppli, T. Qian, J. Mesot, H. Ding and M. Shi

Weyl fermions are two-component spinors described by irreducible representations of the Lorentz group. They are massless with well-defined helicity and move with the speed of light. Although such kind of elementary particles have not been found yet in real space, the charge excitations in a certain class of materials, the Weyl semimetals, are predicted to behave exactly the same as the Weyl fermions, leading to exotic properties like chiral anomaly and quantum anomalous Hall effect. Carrying out angle-resolved photoemission spectroscopy on TaP, a Weyl semimetal candidate, in a wide photon energy range, we observed the pairs of Weyl cones in the bulk electronic states and the unclosed Fermi arcs on the Ta-terminated surface, which fully agree with theoretical calculations. Our results unambiguously establish that TaP is a Weyl semimetal with one type of well-separated Weyl nodes locates at the chemical potential, which guarantee that the exotic low-energy excitations near the Weyl nodes dominate the transport properties, and may lead to novel applications in this nontoxic transition metal monophosphide.

This is well written and highly enlightening. This also represents the fastest theoretical prediction, experimental discovery, detailed technical analysis feedback loop I have ever witnessed, and the most remarkable since the discovery of the pnictide superconductors.

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Happy Tenth Planet Pluto Day – July 14th, 2015

by Tommy on 14/07/2015
Surface Of Tenth Planet Pluto Revealed

Surface Of Tenth Planet Pluto Revealed

Pluto! Ouch. That’s gotta hurt.

Update: All is well!


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Tabletop Black Hole Quantum Information Simulator Envisioned

by Tommy on 14/07/2015

Nambu-Goldstone Effective Theory of Information at Quantum Criticality, Gia Dvali, Andre Franca, Cesar Gomez and Nico Wintergerst

We establish a fundamental connection between quantum criticality of a many-body system, such as Bose-Einstein condensates, and its capacity of information-storage and processing. For deriving the effective theory of modes in the vicinity of the quantum critical point we develop a new method by mapping a Bose-Einstein condensate of N-particles onto a sigma model with a continuous global (pseudo)symmetry that mixes bosons of different momenta. The Bogolyubov modes of the condensate are mapped onto the Goldstone modes of the sigma model, which become gapless at the critical point. These gapless Goldstone modes are the quantum carriers of information and entropy. Analyzing their effective theory, we observe the information-processing properties strikingly similar to the ones predicted by the black hole portrait. The energy cost per qubit of information-storage vanishes in the large-N limit and the total information-storage capacity increases with N either exponentially or as a power law. The longevity of information-storage also increases with N, whereas the scrambling time in the over-critical regime is controlled by the Lyapunov exponent and scales logarithmically with N. This connection reveals that the origin of black hole information storage lies in the quantum criticality of the graviton Bose-gas, and that much simpler systems that can be manufactured in table-top experiments can exhibit very similar information-processing dynamics.

If you knew half of what I know, you would crack under the god damn pressure.

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Twenty (20) Feet of Sea Level Rise Expected With 2C Increase

by Tommy on 10/07/2015

Sea-level rise due to polar ice-sheet mass loss during past warm periods, A. Dutton, A. E. Carlson, A. J. Long, G. A. Milne, P. U. Clark, R. DeConto, B. P. Horton, S. Rahmstorf and M. E. Raymo, Science, Vol. 349, no. 6244 (10 July 2015), DOI: 10.1126/science.aaa4019

Although thermal expansion of seawater and melting of mountain glaciers have dominated global mean sea level (GMSL) rise over the last century, mass loss from the Greenland and Antarctic ice sheets is expected to exceed other contributions to GMSL rise under future warming. To better constrain polar ice-sheet response to warmer temperatures, we draw on evidence from interglacial periods in the geologic record that experienced warmer polar temperatures and higher GMSLs than present. Coastal records of sea level from these previous warm periods demonstrate geographic variability because of the influence of several geophysical processes that operate across a range of magnitudes and time scales. Inferring GMSL and ice-volume changes from these reconstructions is nontrivial and generally requires the use of geophysical models.

Interdisciplinary studies of geologic archives have ushered in a new era of deciphering magnitudes, rates, and sources of sea-level rise. Advances in our understanding of polar ice-sheet response to warmer climates have been made through an increase in the number and geographic distribution of sea-level reconstructions, better ice-sheet constraints, and the recognition that several geophysical processes cause spatially complex patterns in sea level. In particular, accounting for glacial isostatic processes helps to decipher spatial variability in coastal sea-level records and has reconciled a number of site-specific sea-level reconstructions for warm periods that have occurred within the past several hundred thousand years. This enables us to infer that during recent interglacial periods, small increases in global mean temperature and just a few degrees of polar warming relative to the preindustrial period resulted in ≥ 6 m of GMSL rise. Mantle-driven dynamic topography introduces large uncertainties on longer time scales, affecting reconstructions for time periods such as the Pliocene (~ 3 million years ago), when atmospheric CO2 was ~ 400 parts per million (ppm), similar to that of the present. Both modeling and field evidence suggest that polar ice sheets were smaller during this time period, but because dynamic topography can cause tens of meters of vertical displacement at Earth’s surface on million-year time scales and uncertainty in model predictions of this signal are large, it is currently not possible to make a precise estimate of peak GMSL during the Pliocene.

Hear, hear. I know I have hard fossilized coral at 18 feet above mean sea level.

Not the crushed up tsunami emplaced debris or hard baked rock.

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Topological Quantum Matter Physics Primer Finally Published

by Tommy on 7/07/2015

Topological Superconductors and Category Theory, Andrei Bernevig and Titus Neupert, Lecture notes for lectures that were in parts held at: Les Houches Summer School 2014, Vietri Training Course in the Physics of Strongly Correlated Systems 2014, Bogota School on Mathematical Physics 2015

We give a pedagogical introduction to topologically ordered states of matter, with the aim of familiarizing the reader with their axiomatic topological quantum field theory description. We introduce basic noninteracting topological phases of matter protected by symmetries, including the Su-Schrieffer-Heeger model and the one-dimensional p-wave superconductor. The defining properties of topologically ordered states are illustrated explicitly using the toric code and – on a more abstract level – Kitaev’s 16-fold classification of two-dimensional topological superconductors. Subsequently, we present a short review of category theory as an axiomatic description of topological order in two-dimensions. Equipped with this structure, we revisit Kitaev’s 16-fold way.

I can see this is going to take some time.

Time that I do not have.

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Pluto is the Weirdest and Coolest Planet in the Solar System

by Tommy on 6/07/2015
Pluto Weirdest Coolest Planet In The Solar System

Pluto Weirdest Coolest Planet In The Solar System

Cool. Weird. I want more.

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Topological Quantum Physics Hits Precise Mathematical Order

by Tommy on 2/07/2015

A New Kind of Topological Quantum Order: A Dimensional Hierarchy of Quasiparticles Built from Stationary Excitations, Sagar Vijay, Jeongwan Haah and Liang Fu

We introduce exactly solvable models of interacting (Majorana) fermions in d ≥ 3 spatial dimensions that realize a new kind of topological quantum order, building on a model presented in ref. [1]. These models have extensive topological ground-state degeneracy and a hierarchy of point-like, topological excitations that are only free to move within sub-manifolds of the lattice. In particular, one of our models has fundamental excitations that are completely stationary. To demonstrate these results, we introduce a powerful polynomial representation of commuting Majorana Hamiltonians. Remarkably, the physical properties of the topologically-ordered state are encoded in an algebraic variety, defined by the common zeros of a set of polynomials over a finite field. This provides a “geometric” framework for the emergence of topological order.

See also [Ref. 1]:

Majorana Fermion Surface Code for Universal Quantum Computation, Sagar Vijay, Timothy H. Hsieh and Liang Fu

We introduce an exactly solvable model of interacting Majorana fermions realizing Z2 topological order with a Z2 fermion parity grading and lattice symmetries permuting the three fundamental anyon types. We propose a concrete physical realization by utilizing quantum phase slips in an array of phase-locked s-wave superconducting islands on a topological insulator surface. Our model finds a natural application as a Majorana fermion surface code for universal quantum computation, with a single-step stabilizer measurement requiring no physical ancilla qubits, increased error tolerance, and simpler logical gates than a surface code with bosonic physical qubits. We thoroughly discuss protocols for stabilizer measurements, encoding and manipulating logical qubits, and gate implementations.

I finally got around to reading these on my vacation.

I am now officially freaked out.

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Bernie Sanders For President – Rock Concert at the Coliseum

by Tommy on 2/07/2015
Bernie Sanders For Preside - Madison Wisconsin - Coliseum

Bernie Sanders For President – Madison Wisconsin – Coliseum

Those were the days. I wonder what he thinks of space?

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Iron Impurities in Iron Chalcogenide Superconductors Fe(Te,Se) Reveal the Presence of Majorana Bound States

by Tommy on 2/07/2015

Observation of a robust zero-energy bound state in iron-based superconductor Fe(Te,Se), J-X. Yin, Zheng Wu, J-H. Wang, Z-Y. Ye, Jing Gong, X-Y. Hou, Lei Shan, Ang Li, X-J. Liang, X-X. Wu, Jian Li, C-S. Ting, Z-Q. Wang, J-P. Hu, P-H. Hor, H. Ding and S. H. Pan, Nature Physics, 11, 543–546 (22 June 2015), doi:10.1038/nphys3371

In superconductors, electrons are paired and condensed into the ground state. An impurity can break the electron pairs into quasiparticles with energy states inside the superconducting gap. The characteristics of such in-gap states reflect accordingly the properties of the superconducting ground state. A zero-energy in-gap state is particularly noteworthy, because it can be the consequence of non-trivial pairing symmetry or topology. Here we use scanning tunnelling microscopy/spectroscopy to demonstrate that an isotropic zero-energy bound state with a decay length of ~10 Å emerges at each interstitial iron impurity in superconducting Fe(Te,Se). More noticeably, this zero-energy bound state is robust against a magnetic field up to 8 T, as well as perturbations by neighbouring impurities. Such a spectroscopic feature has no natural explanation in terms of impurity states in superconductors with s-wave symmetry, but bears all the characteristics of the Majorana bound state proposed for topological superconductors, indicating that the superconducting state and the scattering mechanism of the interstitial iron impurities in Fe(Te,Se) are highly unconventional.

It’s official. The long awaited revolution has finally arrived.

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Macroscopic Quantum Phase Coherence Coherent Caloritronics

by Tommy on 2/07/2015

Nanoscale phase-engineering of thermal transport with a Josephson heat modulator, Nanoscale phase-engineering of thermal transport with a Josephson heat modulator, Antonio Fornieri, Christophe Blanc, Riccardo Bosisio, Sophie D’Ambrosio and Francesco Giazotto

Macroscopic quantum phase coherence has one of its pivotal expressions in the Josephson effect, which manifests itself both in charge and energy transport. The ability to master the amount of heat transferred through two tunnel-coupled superconductors by tuning their phase difference is the core of coherent caloritronics, and is expected to be a key tool in a number of nanoscience fields, including solid state cooling, thermal isolation, radiation detection, quantum information and thermal logic. Here we show the realization of the first balanced Josephson heat modulator designed to offer full control at the nanoscale over the phase-coherent component of thermal currents. Our device provides magnetic-flux-dependent temperature modulations up to 40 mK in amplitude with a maximum of the flux-to-temperature transfer coefficient reaching 200 mK per flux quantum at a bath temperature of 25 mK. Foremost, it demonstrates the exact correspondence in the phase-engineering of charge and heat currents, breaking ground for advanced caloritronic nanodevices such as thermal splitters, heat pumps and time-dependent electronic engines.

Who did not see this coming?

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Paragon Space Development Prefers CELSS over CELLS

by Tommy on 1/07/2015

CNN Paragon Mars One Article

Paragon Space Development Corporation Mars One CELSS PDF

I do not want to be the one keeping all that hardware running smoothly.

I have a completely different approach. CELLS – Closed Ecological Living and Life Support.

GroX – The Grok Box Grow Box System

GroX Grok Box Website

This has the added advantage that all that polyethylene and polypropylene will make excellent cosmic and solar radiation shielding on the nine month trip to Mars. I was supposed to write this up for NASA and Innocentive by July 6th, but I’m fed up with it. 15K for 100K worth of work? Meh.

By the time these guys get to Mars, solid state and condensed matter physics will have easily achieved the revolutionary advances necessary to completely obsolete this kind of approach.

Thomas Lee Elifritz – Biography

Previous Post on this subject.

If I go to Mars, it will be to retire and chill, not work.

Ceres is where I want to be.

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Edge Mode Superconductivity in a 2D Topological Insulator

by Tommy on 1/07/2015

Edge-mode superconductivity in a two-dimensional topological insulator, Vlad S. Pribiag, Arjan J. A. Beukman, Fanming Qu, Maja C. Cassidy, Christophe Charpentier, Werner Wegscheider and Leo P. Kouwenhoven, Nature Nanotechnology (11 May 2015), doi:10.1038/nnano.2015.86

Topological superconductivity is an exotic state of matter that supports Majorana zero-modes, which have been predicted to occur in the surface states of three-dimensional systems, in the edge states of two-dimensional systems, and in one-dimensional wires. Localized Majorana zero-modes obey non-Abelian exchange statistics, making them interesting building blocks for topological quantum computing. Here, we report superconductivity induced in the edge modes of semiconducting InAs/GaSb quantum wells, a two-dimensional topological insulator. Using superconducting quantum interference we demonstrate gate-tuning between edge-dominated and bulk-dominated regimes of superconducting transport. The edge-dominated regime arises only under conditions of high-bulk resistivity, which we associate with the two-dimensional topological phase. These experiments establish InAs/GaSb as a promising platform for the confinement of Majoranas into localized states, enabling future investigations of non-Abelian statistics.

Update: Here is the published PDF.

See also:

Topological Superconductivity – Edging Closer, Luke Fleet, Nature Physics, 11, 523 (1 July 2015), doi:10.1038/nphys3399

There are three types of fermions in condensed-matter systems: Dirac, Weyl and Majorana. Whereas Dirac fermions are now commonplace thanks to graphene, and experimental evidence for Weyl fermions is growing stronger, Majorana fermions currently remain as elusive as Ettore Majorana himself. Topological superconductors are predicted to host…

Vlad et al. have been working on this for a while. I just noticed he downloaded my essay.

I also just noticed I forgot the st in 21st Century. How embarrassing, lol.

Six months and I never saw it. Proof reading is a science.

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Ceres Crater Bright Spot is a Crack that is Spewing Water Ice

by Tommy on 30/06/2015

Cryovolcanism and/or geysers and water ice is now the leading candidate hypothesis.

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Niobium Phosphide NbP – Extreme Magnetoresistence and Ultrahigh Relativistic Electron Mobility in a Weyl Semimental

by Tommy on 30/06/2015

Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP, Chandra Shekhar, Ajaya K. Nayak, Yan Sun, Marcus Schmidt, Michael Nicklas, Inge Leermakers, Uli Zeitler, Yurii Skourski, Jochen Wosnitza, Zhongkai Liu, Yulin Chen, Walter Schnelle, Horst Borrmann, Yuri Grin, Claudia Felser and Binghai Yan, Nature Physics (22 June 2015), doi:10.1038/nphys3372

Recent experiments have revealed spectacular transport properties in semimetals, such as the large, non-saturating magnetoresistance exhibited by WTe2 (ref. 1). Topological semimetals with massless relativistic electrons have also been predicted as three-dimensional analogues of graphene. These systems are known as Weyl semimetals, and are predicted to have a range of exotic transport properties and surface states, distinct from those of topological insulators. Here we examine the magneto-transport properties of NbP, a material the band structure of which has been predicted to combine the hallmarks of a Weyl semimetal, with those of a normal semimetal. We observe an extremely large magnetoresistance of 850,000% at 1.85 K (250% at room temperature) in a magnetic field of up to 9 T, without any signs of saturation, and an ultrahigh carrier mobility of 5 × 106 cm2 V−1 s−1 that accompanied by strong Shubnikov–de Haas (SdH) oscillations. NbP therefore presents a unique example of a material combining topological and conventional electronic phases, with intriguing physical properties resulting from their interplay.

See also:

An inversion breaking Weyl semimetal state in the TaAs material class, Shin-Ming Huang, Su-Yang Xu, Ilya Belopolski, Chi-Cheng Lee, Guoqing Chang, BaoKai Wang, Nasser Alidoust, Guang Bian, Madhab Neupane, Arun Bansil, Hsin Lin and M. Zahid Hasan, Nature Commun. 6, 7373 (12 June 2015), doi:10.1038/ncomms8373

The recent discoveries of Dirac fermions in graphene and on the surface of topological insulators have ignited worldwide interest in physics and materials science. A Weyl semimetal is an unusual crystal where electrons also behave as massless quasi-particles but interestingly they are not Dirac fermions. These massless particles, Weyl fermions, were originally considered in massless quantum electrodynamics but have not been observed as a fundamental particle in nature. A Weyl semimetal provides a condensed matter realization of Weyl fermions, leading to unique transport properties with novel device applications. Such a semimetal is also a topologically non-trivial metallic phase of matter extending the classification of topological phases beyond insulators. The signature of a Weyl semimetal in real materials is the existence of unusual Fermi arc surface states, which can be viewed as half of a surface Dirac cone in a topological insulator. Here, we identify the first Weyl semimetal in a class of stoichiometric materials, which break crystalline inversion symmetry, including TaAs, TaP, NbAs and NbP. Our first-principles calculations on TaAs reveal the spin-polarized Weyl cones and Fermi arc surface states in this compound. We also observe pairs of Weyl points with the same chiral charge which project onto the same point in the surface Brillouin zone, giving rise to multiple Fermi arcs connecting to a given Weyl point. Our results show that TaAs is the first topological semimetal identified which does not depend on fine-tuning of chemical composition or magnetic order, greatly facilitating an exploration of Weyl physics in real materials.

Published as: A Weyl Fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class, Shin-Ming Huang, Su-Yang Xu, Ilya Belopolski, Chi-Cheng Lee, Guoqing Chang, BaoKai Wang, Nasser Alidoust, Guang Bian, Madhab Neupane, Chenglong Zhang, Shuang Jia, Arun Bansil, Hsin Lin and M. Zahid Hasan, Nature Commun. 6, 7373 (12 June 2015), doi:10.1038/ncomms8373

Weyl fermions are massless chiral fermions that play an important role in quantum field theory but have never been observed as fundamental particles. A Weyl semimetal is an unusual crystal that hosts Weyl fermions as quasiparticle excitations and features Fermi arcs on its surface. Such a semimetal not only provides a condensed matter realization of the anomalies in quantum field theories but also demonstrates the topological classification beyond the gapped topological insulators. Here, we identify a topological Weyl semimetal state in the transition metal monopnictide materials class. Our first-principles calculations on TaAs reveal its bulk Weyl fermion cones and surface Fermi arcs. Our results show that in the TaAs-type materials the Weyl semimetal state does not depend on fine-tuning of chemical composition or magnetic order, which opens the door for the experimental realization of Weyl semimetals and Fermi arc surface states in real materials.

The phosphides and Group Vs have finally arrived, apparently. Better late than never.

‘Extreme’ and ‘ultra’ are new the new condensed matter physics catchwords.

Phosphine and bismuthine under pressure are suddenly looking good.

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A Bad Day in Launch Control For SpaceX and the United States

by Tommy on 28/06/2015

The loss of coffee for the Gemini 7 espresso machine is going to be almost unbearable.

Condolences all around. Shit happens. Usually at the worst possible time.

Chemical reaction engines (aka rockets) are like that.

The reactions should be interesting.

Update: After thinking this over my first wild uninformed speculative guess is moisture and ice. I’m in Florida now and it has been ridiculously hot, moist and wet here and we’re at the height of summer. It wouldn’t take much – minor oversight in air conditioning or exposure in some valves.

Update 2: It’s looking more like structural failure in the upper stage oxygen tank dome area. Defect or deformation in manufacturing or payload mating procedures. But it could be anything.

Gary Hudson has an interesting hypothesis that tracks back to the helium pressurization system, making the dome failure a symptom rather than the cause, and so it still could be something as simple as moisture. There is a known history of helium pressurization problems.

Update 3: Another hypothesis being put forth is related to a dynamic resonant instability of a 500 kilogram docking adapter payload slightly stressing the upper stage oxygen dome welds. This is a three point suspension arrangement in the Dragon trunk that may have been vibrating.

I can see how the non-intuitiveness of all this is going to take some time to sort out. Since there was an over pressure event, the pressurization system seems to be at fault, but one has to sort out the cascading avalanche of symptoms from the disease. Is there a doctor in the house?

Oh well. VEGGIE units to the rescue!

Eat healthy. Get smart.

Final Update: It was a structural failure of a strut holding a COPV helium pressurization tank.

One in a thousand failure at 3.2 gees’ of acceleration.

It’s always something. It’s never nothing.

Ok, back to the grind everyone.

That’s an order! lol.

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Cosmic Weather Report – Absolutely Perfectly Crystal Clear

by Tommy on 27/06/2015
Of Course I Still Love You

Of Course I Still Love You

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Bismuth Adatoms on Graphene on Silicon Carbide Reported

by Tommy on 27/06/2015

Tailoring low-dimensional structures of bismuth on monolayer epitaxial graphene, H.-H. Chen, S. H. Su, S.-L. Chang, B.-Y. Cheng, S. W. Chen, H.-Y. Chen, M.-F. Lin and J. C. A. Huang, Scientific Reports, 5, 11623 (23 June 2015), doi:10.1038/srep11623

To improve graphene-based multifunctional devices at nanoscale, a stepwise and controllable fabrication procedure must be elucidated. Here, a series of structural transition of bismuth (Bi) adatoms, adsorbed on monolayer epitaxial graphene (MEG), is explored at room temperature. Bi adatoms undergo a structural transition from one-dimensional (1D) linear structures to two-dimensional (2D) triangular islands and such 2D growth mode is affected by the corrugated substrate. Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms. When annealed to ~ 500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size. A well-controlled fabrication method is thus demonstrated. The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices.

First of all, this is just another reporting of a previous result published in Carbon. Same results, same authors, different journal. At least this report is open and includes some more information.

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SpaceX and Blue Origin Call For New Reusable Cryogenic Engines, Propulsion and Launch Vehicle Development

by Tommy on 27/06/2015

Congressional Testimony of Jeffrey Thornburg – SpaceX.

An alternative approach, and consistent with the U.S. Air Force’s current planning, SpaceX recommends that Congress allow for a broader set of investments into propulsion technologies, prototypes, test infrastructure, and advanced systems in order to enhance the U.S. liquid propulsion industrial base more broadly than an effort to fund a single engine (with potentially retrograde technology) would ever do.

Congressional Testimony of Robert Meyerson – Blue Origin

The U.S. industrial base now includes a number of commercial companies, like Blue Origin, that have developed significant liquid propulsion capabilities with private investment. We’re spending our own money, rather than taxpayer’s funds, and we are taking a “clean sheet” approach to development. We have invested in modern manufacturing equipment and processes to maximize production efficiency. We aren’t burdened by unused capacity that so often gets billed back to the Government in the form of high overhead rates. As a result, we are able to out compete the Russians, building modern, American engines on flexible production lines to serve multiple launch vehicles.

Is there another billionaire with an ego in the house?

My money’s on the kid with the rocket.

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Antonin Scalia Says – Keep Off My Lawn You Dirty Hippie

by Tommy on 26/06/2015
Don't Step On My Lawn You Dirty Hippie

Don’t Step On My Lawn You Dirty Hippie

Excuse me, Sir, I’m so sorry. Please accept my sincerest apologies.

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Laurentide Ice Sheet Esker Formation and Subglacial Drainage

by Tommy on 26/06/2015

An ice-sheet scale comparison of eskers with modelled subglacial drainage routes, Stephen J. Livingstone, Robert D. Storrar, John K. Hillier, Chris R. Stokes, Chris D. Clark and Lev Tarasov, Geomorphology, 246, 104–112 (1 October 2015), doi:10.1016/j.geomorph.2015.06.016

Eskers record the signature of channelised meltwater drainage during deglaciation providing vital information on the nature and evolution of subglacial drainage. In this paper, we compare the spatial pattern of eskers beneath the former Laurentide Ice Sheet with subglacial drainage routes diagnosed at discrete time intervals from the results of a numerical ice-sheet model. Perhaps surprisingly, we show that eskers predominantly occur in regions where modelled subglacial water flow is low. Eskers and modelled subglacial drainage routes were found to typically match over distances of < 10 km, and most eskers show a better agreement with the routes close to the ice margin just prior to deglaciation. This supports a time-transgressive esker pattern, with formation in short (< 10 km) segments of conduit close behind a retreating ice margin, and probably associated with thin, stagnant or sluggish ice. Esker-forming conduits were probably dominated by supraglacially fed meltwater inputs. We also show that modelled subglacial drainage routes containing the largest concentrations of meltwater show a close correlation with palaeo-ice stream locations. The paucity of eskers along the terrestrial portion of these palaeo-ice streams and meltwater routes is probably because of the prevalence of distributed drainage and the high erosion potential of fast-flowing ice.

Open Access Funded by the Natural Environment Research Council in the United Kingdom.

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Quantum Light Proposed For Ultracold Atomic Gases

by Tommy on 26/06/2015

Probing and Manipulating Fermionic and Bosonic Quantum Gases with Quantum Light
Thomas J. Elliott, Gabriel Mazzucchi, Wojciech Kozlowski, Santiago F. Caballero-Benitez and Igor B. Mekhov

We study the atom-light interaction in the fully quantum regime, with focus on off-resonant light scattering into a cavity from ultracold atoms trapped in an optical lattice. The detection of photons allows the quantum nondemolition (QND) measurement of quantum correlations of the atomic ensemble, distinguishing between different quantum states. We analyze the entanglement between light and matter and show how it can be exploited for realizing multimode macroscopic quantum superpositions such as Schrödinger cat states, for both bosons and fermions. We provide examples utilizing different measurement schemes, and study their robustness to decoherence. Finally, we address the regime where the optical lattice potential is a quantum dynamical variable and is modified by the atomic state, leading to novel quantum phases, and significantly altering the phase diagram of the atomic system.

Wow. Just wow.

In summary, we have shown how to use light scattering from ultracold atoms to perform QND measurements on fermionic systems, and demonstrated how the quantum addition to the classical diffraction pattern carries information about quantum correlations of the atomic state. Focusing on a single experimental run, we discussed the entanglement properties between light and matter and showed how these can be exploited for creating macroscopic quantum superpositions with fermionic and bosonic systems. We provided different schemes for the realization of such states and suggested how to make them more robust to decoherence by using a homodyne measurement. Finally, we described the phase diagram of a system of bosons in an optical cavity trapped in an optical lattice. The cavity mediates an effective long-range interaction which stabilizes a superfluid state with minimal fluctuations and suppresses the Mott insulator states.

I will donate my cat if it will help.

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Of Course I Still Love You More Than Coffee

by Tommy on 25/06/2015
Of Course I Still Love You - SpaceX Drone Ship - ASDS

Of Course I Still Love You – SpaceX Drone Ship – ASDS

But don’t make me prove it … again.

Photo: Ben Cooper/SpaceX.

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Dramatically Improved Spin Polarimeter Tested on Bismuth (111)

by Tommy on 25/06/2015

Multi-channel exchange-scattering spin polarimetry, Fuhao Ji, Tan Shi, Mao Ye, Weishi Wan, Zhen Liu, Jiajia Wang, Tao Xu and Shan Qiao

Electron spin takes critical role in almost all novel phenomena discovered in modern condensed matter physics (High-temperature superconductivity, Kondo effect, Giant Magnetoresistance, topological insulator, quantum anomalous Hall effect, etc.). However, the measurements for electron spin is of poor quality which blocks the development of material sciences because of the low efficiency of spin polarimeter. Here we show an imaging type exchange-scattering spin polarimeter with 5 orders more efficiency compared with a classical Mott polarimeter. As a demonstration, the fine spin structure of electronic states in bismuth (111) is investigated, showing the strong Rashba type spin splitting behavior in both bulk and surface states. This improvement pave the way to study novel spin related phenomena with unprecedented accuracy.

All Hail The Probe!

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30 nm Bismuth Bi (111) Films on Bi2Te3 Substrate Investigated

by Tommy on 19/06/2015

Topologically Nontrivial Bismuth(111) Thin Films Grown on Bi2Te3, Meng-Yu Yao, Fengfeng Zhu, Lin Miao, C. Q. Han, Fang Yang, D. D. Guan, C. L. Gao, Canhua Liu, Dong Qian and Jin-feng Jia

Using high-resolution angle-resolved photoemission spectroscopy, the electronic structure near the Fermi level and the topological property of the Bi(111) films grown on the Bi2Te3(111) substrate were studied. Very different from the bulk Bi, we found another surface band near the M¯ point besides the two well-known surface bands on the Bi(111) surface. With this new surface band, the bulk valence band and the bulk conduction band of Bi can be connected by the surface states. Our band mapping revealed odd number of Fermi crossings of the surface bands, which provided a direct experimental signature that Bi(111) thin films of a certain thickness on the Bi2Te3(111) substrate can be topologically nontrivial in three dimensions.

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