Pressure Induced Superconductivity in Tantalum Ditelluride

by Tommy on 27/04/2017
Tantalum Ditelluride Phase Diagram

Tantalum Ditelluride Phase Diagram

Here is something interesting.

Separation of the charge density wave and superconducting states by an intermediate semimetal phase in pressurized TaTe2, Jing Guo, Huixia Luo, Huaixin Yang, Linlin Wei, Honghong Wang, Wei Yi, Yazhou Zhou, Zhe Wang, Shu Cai, Shan Zhang, Xiaodong Li, Yanchun Li, Jing Liu, Ke Yang, Aiguo Li, Jianqi Li, Qi Wu, Robert J Cava and Liling Sun (26 April 2017)

In layered transition metal dichalcogenides (LTMDCs) that display both charge density waves (CDWs) and superconductivity, the superconducting state generally emerges directly on suppression of the CDW state. Here, however, we report a different observation for pressurized TaTe2, a non-superconducting CDW-bearing LTMDC at ambient pressure. We find that a superconducting state does not occur in TaTe2 after the full suppression of its CDW state, which we observe at about 3 GPa, but, rather, a non-superconducting semimetal state is observed. At a higher pressure, ~ 21 GPa, where both the semimetal state and the corresponding positive magnetoresistance effect are destroyed, superconductivity finally emerges and remains present up to ~ 50 GPa, the high pressure limit of our measurements. Our pressure-temperature phase diagram for TaTe2 demonstrates that the CDW and the superconducting phases in TaTe2 do not directly transform one to the other, but rather are separated by a semimetal state, – the first experimental case where the CDW and superconducting states are separated by an intermediate phase in LTMDC systems.

I again remind my faithful readers that I utterly failed to predict this result way back in 1994.

No Comments

Chern Simons Theory of Composite Fermions Developed

by Tommy on 26/04/2017

This is how one begins to do quantum cosmology.

Chern-Simons Theory and Dynamics of Composite Fermions, Junren Shi (25 April 2017)

We propose a Chern-Simons field theoretical description of the fractional quantum Hall effect in 1+4 dimensions. It suggests that composite fermions reside on a momentum manifold with a nonzero Chern number. Based on derivations from microscopic wave functions, we further show that the momentum manifold has a uniformly distributed Berry curvature. As a result, composite fermions do not follow the ordinary Newtonian dynamics as commonly believed, but the more general symplectic one. For a Landau level with the particle-hole symmetry, the theory correctly predicts its Hall conductance at half-filling as well as the symmetry between an electron filling fraction and its hole counterpart.

If someone were to fund me, I might have time to do something about this problem.

Symplectic mechanics was something that I did study.

No Comments

Jarzynski Equality – Brownian Motion and Einstein Coefficients

by Tommy on 26/04/2017

Finally, here is the real deal. Fred Gittes is the next Udo Seifert.

Two famous results of Einstein derived from the Jarzynski equality, Fred Gittes, To Appear in Am. J. Phys (25 April 2017)

The Jarzynski equality (JE) is a remarkable statement relating transient irreversible processes to infinite-time free energy differences. Although twenty years old, the JE remains unfamiliar to many; nevertheless it is a robust and powerful law. We examine two of Einstein’s most simple and well-known discoveries, one classical and one quantum, and show how each of these follows from the JE. Our first example is Einstein’s relation between the drag and diffusion coefficients of a particle in Brownian motion. In this context we encounter a paradox in the macroscopic limit of the JE which is fascinating, but also warns us against using the JE too freely outside of the microscopic domain. Our second example is the equality of Einstein’s B coefficients for absorption and stimulated emission of quanta. Here resonant light does irreversible work on a sample, and the argument differs from Einstein’s equilibrium reasoning using the Planck black-body spectrum. We round out our examples with a brief derivation and discussion of Jarzynski’s remarkable equality.

Take your time with this, it’s an extremely difficult but interesting evolving subject.

Comments: This is a pedagogical paper

No Comments

Strongly Coupled P-Wave Superfluids May be Unstable

by Tommy on 26/04/2017

Ok, now I’m going to get into the good stuff. And the hard stuff. Pay attention!

Two-dimensional Fermi gases near a p-wave resonance, Shao-Jian Jiang and Fei Zhou (25 April 2017)

We study the stability of p-wave superfluidity for two-dimensional Fermi gases near a p-wave Feshbach resonance. A systematic analysis is carried out in the limit when the interchannel coupling is strong. We show that a homogeneous p-wave pairing is actually unstable due to quantum fluctuations, in contrast to the previously predicted p + ip superfluid in the weak-coupling limit [V. Gurarie et al., Phys. Rev. Lett. 94, 230403 (2005)]. This indicates an onset of instability at certain intermediate interchannel coupling strength. Alternatively, the instability can also be driven by lowering the particle density.

It’s not so much the results that they produce here but the techniques they use.

You can always work around or exploit instabilities.

That’s the whole point, right?

No Comments

Simple Clear Review Assessment of Thermoelectricity Science

by Tommy on 26/04/2017

Here is another great review I wish I had at my disposal 25 years ago now.

Thermoelectric Devices: Principles and Future Trends, Ibrahim M Abdel-Motaleb and Syed M. Qadri (25 April 2017)

The principles of the thermoelectric phenomenon, including Seebeck effect, Peltier effect, and Thomson effect are discussed. The dependence of the thermoelectric devices on the figure of merit, Seebeck coefficient, electrical conductivity, and thermal conductivity are explained in details. The paper provides an overview of the different types of thermoelectric materials, explains the techniques used to grow thin films for these materials, and discusses future research and development trends for this technology.

Again, well done, Sirs.

No Comments

Weyl Metals Reviewed

by Tommy on 26/04/2017

The gentleman has published a series of great reviews of these kinds of subjects.

Weyl Metals, A. A. Burkov, Submitted to Annual Reviews of Condensed Matter Physics (25 April 2017)

Weyl metal is the first example of a conducting material with a nontrivial electronic structure topology, making it distinct from an ordinary metal. Unlike in insulators, the nontrivial topology is not related to invariants, associated with completely filled bands, but with ones, associated with the Fermi surface. The Fermi surface of a topological metal consists of disconnected sheets, each enclosing a Weyl node, which is a point of contact between two nondegenerate bands. Such a point contact acts as a source of Berry curvature, or a magnetic monopole in momentum space. Its charge, or the flux of the Berry curvature through the enclosing Fermi surface sheet, is a topological invariant. We review the current state of this rapidly growing field, with a focus on bulk transport phenomena in topological metals.

The new quantum cosmology.

No Comments

Axion Physics Found In Dense QCD Equations of State

by Tommy on 26/04/2017

Since I’m on the subject, here is more on this remarkable region of quantum physics.

Anomalous Transport Properties of Dense QCD in a Magnetic Field, Vivian de la Incera (23 April 2017)

Despite recent advancements in the study and understanding of the phase diagram of strongly interacting matter, the region of high baryonic densities and low temperatures has remained difficult to reach in the lab. Things are expected to change with the planned HIC experiments at FAIR in Germany and NICA in Russia, which will open a window to the high-density-low-temperature segment of the QCD phase map, providing a unique opportunity to test the validity of model calculations that have predicted the formation of spatially inhomogeneous phases with broken chiral symmetry at intermediate-to-high densities. Such a density region is also especially relevant for the physics of neutron stars, as they have cores that can have several times the nuclear saturation density. On the other hand, strong magnetic fields, whose presence is fairly common in HIC and in neutron stars, can affect the properties of these exotic phases and lead to signatures potentially observable in these two settings. In this paper, I examine the anomalous transport properties produced by the spectral asymmetry of the lowest Landau level (LLL) in a QCD-inspired NJL model with a background magnetic field that exhibits chiral symmetry breaking at high density via the formation of a Dual Chiral Density Wave (DCDW) condensate. It turns out that in this model the electromagnetic interactions are described by the axion electrodynamics equations and there is a dissipationless Hall current.

Based on work done in collaboration with Efrain J Ferrer.

Well done, Sir and Madam.

No Comments

Dense Neutron Star Exotic Matter Simulated By Cold Atoms

by Tommy on 26/04/2017

Another round of super cold breakthroughs that I don’t have time or money to cover.

What can I do when I’ve already solved the major outstanding problems of our time?

Neutron Stars in the Laboratory, Vanessa Graber, Nils Andersson and Michael Hogg, Accepted for Publication in International Journal of Modern Physics D (1 March 2017)

Neutron stars are astrophysical laboratories of many extremes of physics. Their rich phenomenology provides insights into the state and composition of matter at densities which cannot be reached in terrestrial experiments. Since the core of a mature neutron star is expected to be dominated by superfluid and superconducting components, observations also probe the dynamics of large-scale quantum condensates. The testing and understanding of the relevant theory tends to focus on the interface between the astrophysics phenomenology and nuclear physics. The connections with low-temperature experiments tend to be ignored. However, there has been dramatic progress in understanding laboratory condensates (from the different phases of superfluid helium to the entire range of superconductors and cold atom condensates). In this review, we provide an overview of these developments, compare and contrast the mathematical descriptions of laboratory condensates and neutron stars and summarise the current experimental state-of-the-art. This discussion suggests novel ways that we may make progress in understanding neutron star physics using low-temperature laboratory experiments.

I could robotify or scriptify these posts, but then I wouldn’t have to actually read this stuff first.

I can safely say that I predicted this, though. And I can prove it!

Neutron stars are one step away from nothingness.

Failed nothings, they are. Like me.

No Comments

Happy Earth Day! Again.

by Tommy on 23/04/2017

Are we there yet?

No Comments

Efficient Exciton Plasmon Photo Emission and Absorption

by Tommy on 20/04/2017

It’s time to admit the exciton plasmon coupling era is upon us.

Proposal of highly efficient photoemitter with strong photon-harvesting capability and exciton superradiance, Takuya Matsuda and Hajime Ishihara (15 April 2017)

We propose a system of highly efficient photoemitters comprising metal-dielectric (plasmonic-excitonic) multilayered structures. In the proposed structure, the absorption in the excitonic layer is greatly enhanced through quantum interference between the split modes arising from the coupling of the layered excitons and the plasmons sustained by the metallic layer. Furthermore, the large interaction volume between surface plasmons and excitons causes exciton superradiance, which results in the extremely efficient photoemission. This finding indicates the possibility of designing highly efficient photoemitters based on simple layered structures.

So what is not to like about this?

No Comments

New Giant Planar Hall Effect Signals Axial Anomaly Presence

by Tommy on 20/04/2017

Lars Onsagar would love chemical physics right now.

Giant Planar Hall Effect in Topological Metals, A. A. Burkov (18 April 2017)

Much excitement has been generated recently by the experimental observation of the chiral anomaly in condensed matter physics. This manifests as strong negative longitudinal magnetoresistance and has so far been clearly observed in Na3Bi, ZrTe5 and GdPtBi. In this work we point out that the chiral anomaly must lead to another effect in topological metals, that has been overlooked so far: Giant Planar Hall Effect (GPHE), which is the appearance of a large transverse voltage when the in plane magnetic field is not aligned with the current. Moreover, we demonstrate that the GPHE is closely related to the angular narrowing of the negative longitudinal magnetoresistance signal, observed experimentally.

I had blogged Mr. Burkov earlier, he knows what he’s talking about.

No Comments

The Trump Russia Dossier

by Tommy on 19/04/2017
Trump Russia Dossier

Trump Russia Dossier

Happy 420 Day!

No Comments

MADMAX Dark Matter Axion Haloscope White Paper Released

by Tommy on 18/04/2017

There were quite a few breakthroughs on the ArXiV last night, which I don’t have time to cover right now, but I found this axion haloscope white paper on Scholar that needs to be fast tracked. You know, because of ‘gravitational axions’.

A new experimental approach to probe QCD Axion Dark Matter in the mass range above 40μeV, P. Brun, A. Caldwell, L. Chevalier, G. Dvali, E. Garutti, C. Gooch, A. Hambarzumjan, S. Knirck, M. Kramer, H. Kruger, T. Lasserre, A. Lindner, B. Majorovits C. Martens, A. Millar, G. Raffelt, J. Redondo , O. Reimann, A. Schmidt, F. Simon, F. Steffen, G. Wieching, The MADMAX Interest Group (20 March 2017)

Axions represent a class of particles that emerge in theoretical models explaining several mysteries of high-energy particle physics and cosmology. They explain the absence of CP violation in the strong interaction, provide dark matter candidates, and can be responsible for inflation and structure formation in the early universe. Several searches for axions and axion-like particles have constrained the parameter space over the last decades, however, no hints of axions have been found. The mass range of 1–1000 μeV remains highly attractive and well motivated region for dark matter axions. In this white paper we present a description of a new experiment based on the concept of a dielectric haloscope for the search for dark matter axions in the mass range 40–400 μeV. The experiment, called MADMAX, will consist of several parallel dielectric layers, whose separations can be adjusted and are placed in a strong magnetic field. This would lead to the emission of axion induced electromagnetic waves in the 10–100 GHz domain, with the frequency given by the axion mass.

Now all I have to do is read this white paper.

The race to the gravitational axion is on!

No Comments

High Mass-Energy Axions Excluded by LUX WIMP Search

by Tommy on 14/04/2017

I didn’t realize they would try this but I guess it’s a no brainer

I’m not listing all of the damn authors here though.

First searches for axions and axion-like particles with the LUX experiment, D.S. Akerib, et al., The LUX Collaboration, (7 April 2017)

The first searches for axions and axion-like particles with the Large Underground Xenon (LUX) experiment are presented. Under the assumption of an axio-electric interaction in xenon, the coupling constant between axions and electrons, gAe is tested, using data collected in 2013 with an exposure totalling 95 live-days × 118 kg. A double-sided, profile likelihood ratio statistic test excludes gAe larger than 3.5 × 10−12 (90% C.L.) for solar axions. Assuming the DFSZ theoretical description, the upper limit in coupling corresponds to an upper limit on axion mass of 0.12 eV/c2, while for the KSVZ description masses above 36.6 eV/c2 are excluded. For galactic axion-like particles, values of gAe larger than 4.2 × 10−13 are excluded for particle masses in the range 1-16 keV/c2. These are the most stringent constraints to date for these interactions.

I like my gravitational axions better, obviously, but they do have a good explanation of axions.

Our axions in this universe just happen to be super cool axions.

So what’s not to like about that? We’re so special.

No Comments

Proto Autobiogenesis on the Saturn Ice Moon World Enceladus

by Tommy on 13/04/2017
Saturn Ice Moon World Enceladus

Saturn Ice Moon World Enceladus

I don’t have even a link yet but this will make my blob look better anyways.

That had to be the most painful NASA press conference I ever had to shut right off. Cringeful.

No Comments

Dark Matter Cosmic Web Void Filament Imaging Refined

by Tommy on 12/04/2017
Galactic Dark Matter Halo Filaments

Galactic Dark Matter Halo Filaments

Particulate dark matter seems to be confirmed now.

I can only suggest that the gravitational axion detection will happen soon.

The weak-lensing masses of filaments between luminous red galaxies, Seth D. Epps and Michael J. Hudson, Monthly Notices of the Royak Astronomical Society, MNRAS, 468 (3): 2605-2613 (1 Narch 2017), DOI:10.1093/mnras/stx517

In the standard model of non-linear structure formation, a cosmic web of dark-matter-dominated filaments connects dark matter haloes. In this paper, we stack the weak lensing signal of an ensemble of filaments between groups and clusters of galaxies. Specifically, we detect the weak lensing signal, using CFHTLenS galaxy ellipticities, from stacked filaments between Sloan Digital Sky Survey (SDSS)-III/Baryon Oscillation Spectroscopic Survey luminous red galaxies (LRGs). As a control, we compare the physical LRG pairs with projected LRG pairs that are more widely separated in redshift space. We detect the excess filament mass density in the projected pairs at the 5σ level, finding a mass of (1.6 ± 0.3) × 1013 M for a stacked filament region 7.1 h−1 Mpc long and 2.5 h−1 Mpc wide. This filament signal is compared with a model based on the three-point galaxy–galaxy-convergence correlation function, as developed in Clampitt et al., yielding reasonable agreement.

I can comment where this is going though. Although I am not convinced yet either way about sub-horizon (dark energy) inhomogenieties, it’s clear the baryons are migrating into the dark matter filaments (I guess that’s standard terminology now), and the cosmic webs and voids are indeed inhomogenieties looking very much like a nanoscale (or in our case, megascale) phase separation into bosonic remnants of a node-line-sheet structure – which very much looks like domain wall disintegration and dissipation. Therefore the ‘gravitational axion’ paradigm I have proposed at the first of the year still holds. In my opinion, it firmly holds, and quite honestly the hypothesis is the last man standing, irrespective of the actual composite nature or structure of the bosons and/or excitons making up the dark matter. It still could be anything, but clearly this goes well beyond sterile QCD axions in my humble opinion. But alas, I would still take a sterile axion if that turns out to be the case. I’m very flexible with this as long as progress continues to be made. I’m looking for absolute exclusion of low scale SUSY, WIMPS and MACHOs, MOGs entropic gravity, although MACHOs are done and I still believe there is room for entropic gravity.

Somewhere. Over the rainbow. That’s it. I feel another song comin on … You know the story.

Rest in peace, Vera Rubin. 1928-2016.

No Comments

Collective Modes by Higgs’ Mechanism Obey Nambu’s Identity

by Tommy on 11/04/2017

This is a real eye opener.

Nambu identity and collective modes in superconductors and superfluid 3He, Gavriil Shchedrin and David M. Lee (7 April 2017)

Collective modes manifest themselves in a variety of different physical systems ranging from superconductors to superfluid 3He. The collective modes are generated via the Higgs-Anderson mechanism that is based on the symmetry breaking double well potential. Recently collective modes were explored in superconducting NbN and InO in the presence of a strong terahertz laser field. In both cases a single collective mode that oscillates with twice the frequency of the superconducting energy gap Δ was discovered. Superfluid 3He is the host for a whole variety of collective modes. In particular, in the superfluid 3He B-phase, two massive collective modes were found with masses √8̅/̅5̅ Δ and √1̅2̅/̅5̅ Δ. We show that for both cases of the superconducting films and for the superfluid 3He B-phase, the collective modes satisfy the Nambu identity that relates the masses of different collective modes to the energy gap parameter Δ.

This paper is mathematical elegance, personified.

No Comments

Exciton Plasmon Coupling Found in Tungsten Dichalcogenides

by Tommy on 10/04/2017

This is something you’ll definitely want for your superconducting plasma warp core.

Marrying excitons and plasmons in monolayer transition-metal dichalcogenides, Dinh Van Tuan, Benedikt Scharf, Igor Žutić and Hanan Dery (6 April 2017)

Just as photons are the quanta of light, plasmons are the quanta of orchestrated charge-density oscillations in conducting media. Plasmon phenomena in normal metals, superconductors and doped semiconductors are often driven by long-wavelength Coulomb interactions. However, in crystals whose Fermi surface is comprised of disconnected pockets in the Brillouin zone, collective electron excitations can also attain a shortwave component when electrons transition between these pockets. Here, we show that the band structure of monolayer transition-metal dichalcogenides gives rise to an intriguing mechanism through which shortwave plasmons are paired up with excitons. The coupling elucidates the origin for the optical side band that is observed repeatedly in monolayers of WSe2 and WS2 but not understood. The theory makes it clear why exciton-plasmon coupling has the right conditions to manifest itself distinctly only in the optical spectra of electron-doped tungsten-based monolayers.

It sounds like a marriage made in hell.

No Comments

Yakutite Nanodiamond is Impact Ejecta from the Popigai Crater

by Tommy on 10/04/2017

There is a bit more to report on the ongoing lonsdaleite saga. It’s not quite a war. Yet. But close.

Mineralogical and crystallographic features of polycrystalline yakutite diamond, Hiroaki Ohfuji, Motosuke Nakaya, Alexander P. Yelissevev, Valentin P. Afanasiev and Konstantin D. Litasov, Journal of Mineralogical and Petrological Sciences, 112, 46-51 (1 February 2017), doi:10.2465/jmps.160719g

This study revealed for the first time the microtexture and crystallographic features of natural polycrystalline diamond, yakutite found in placer deposits in the Siberian Platform, Russia. Yakutite consists of well–sintered nanocrystalline (5–50 nm) diamond and small amount of lonsdaleite showing distinct preferred orientations. Micro–focus X–ray and electron diffractions showed a coaxial relationship between lonsdaleite 100 and diamond 111, suggesting the martensitic formation of yakutite from crystalline graphite. These textural and crystallographic features are well comparable to those of the impact diamonds from the Popigai crater located in the central Siberia and strongly support the idea that yakutite is a product of long–distance outburst from the Popigai crater, which has been inferred merely from the geochemical signatures.

See also:

Investigation on the formation of lonsdaleite from graphite, V. A. Greshnyakov and E. A. Belenkov, Journal of Experimental and Theoretical Physics, 124, 2, 265–274 (23 March 2017), DOI:10.1134/S1063776117010125

Structural stability and the possible pathways to experimental formation of lonsdaleite—a hexagonal 2H polytype of diamond—have been studied in the framework of the density functional theory (DFT). It is established that the structural transformation of orthorhombic Cmmm graphite to 2H polytype of diamond must take place at a pressure of 61 GPa, while the formation of lonsdaleite from hexagonal P6/mmm graphite must take place at 56 GPa. The minimum potential barrier height separating the 2H polytype state from graphite is only 0.003 eV/atom smaller than that for the cubic diamond. The high potential barrier is indicative of the possibility of stable existence of the hexagonal diamond under normal conditions. In this work, we have also analyzed the X-ray diffraction and electron-microscopic data available for nanodiamonds found in meteorite impact craters in search for the presence of hexagonal diamond. Results of this analysis showed that pure 3C and 2H polytypes are not contained in the carbon materials of impact origin, the structure of nanocrystals found representing diamonds with randomly packed layers. The term “lonsdaleite,” used to denote carbon materials found in meteorite impact craters and diamond crystals with 2H polytype structure, is rather ambiguous, since no pure hexagonal diamond has been identified in carbon phases found at meteorite fall sites.

So lonsdaleite lives! But only fleetingly in impact nanodiamonds.

Shear strain is still the key to making lonsdaleite.

Exploding missiles is not the best way.

It takes nuance and finesse.

No Comments

Heavy Particle Beyond Standard Model Physics Is Limited

by Tommy on 8/04/2017

This should give any MACHO WIMPS pause for thought.

Pulsar Timing Constraints on Physics Beyond the Standard Model, Niayesh Afshordi, Hyungjin Kim and Elliot Nelson (15 March 2017)

We argue that massive quantum fields source low-frequency long-wavelength metric fluctuations through the quantum fluctuations of their stress-energy, given reasonable assumptions about the analytic structure of its correlators. This can be traced back to the non-local nature of the gauge symmetry in General Relativity, which prevents an efficient screening of UV scales (what we call the cosmological non-constant problem). We define a covariant and gauge-invariant observable which probes line-of-sight spacetime curvature fluctuations on an observer’s past lightcone, and show that current pulsar timing data constrains any massive particle to m ≲ 600 GeV. This astrophysical bound severely limits the possibilities for physics beyond the standard model below the scale of quantum gravity.

This new empirical prediction seems to be in direct conflict with their previous post-Higgs, pre-upgraded-LHC theoretical prediction of imminent TeV scale physics. Fortunately, the cosmic QCD ‘gravitational’ axion is exempt from this. That prediction was archived here for posterity.

Cosmological bounds on TeV-scale physics and beyond, Niayesh Afshordi and Elliot Nelson, Phys. Rev. D 93, 083505 (7 April 2016), DOI:10.1103/PhysRevD.93.083505

We study the influence of the fluctuations of a Lorentz invariant and conserved vacuum on cosmological metric perturbations, and show that they generically blow up in the IR. We compute this effect using the Källén-Lehmann spectral representation of stress correlators in generic quantum field theories, as well as the holographic bound on their entanglement entropy, both leading to an IR cut-off that scales as the fifth power of the highest UV scale (in Planck units). One may view this as analogous to the Heisenberg uncertainty principle, which is imposed on the phase space of gravitational theories by the Einstein constraint equations. The leading effect on cosmological observables come from anisotropic vacuum stresses which imply: i) any extension of the standard model of particle physics can only have masses (or resonances) ≲ 24 TeV, and ii) perturbative quantum field theory or quantum gravity becomes strongly coupled beyond a cut-off scale of Λ ≲ 1 PeV. Such a low cut-off is independently motivated by the Higgs hierarchy problem. This result, which we dub the cosmological non-constant problem, can be viewed as an extension of the cosmological constant (CC) problem, demonstrating the non-trivial UV-IR coupling and (yet another) limitation of effective field theory in gravity. However, it is more severe than the old CC problem, as vacuum fluctuations cannot be tuned to cancel due to the positivity of spectral densities or entropy. We thus predict that future advances in cosmological observations and collider technology will sandwich from above and below, and eventually discover, new (non-perturbative) physics beyond the Standard Model within the TeV-PeV energy range.

This was in the 750 GeV bump era, so it appears the sandwich has closed.

The empirical prediction seems more persuasive.

No Comments

Highly Speculative Quantum Gravity Hypothesis Explored

by Tommy on 8/04/2017

Sorry, I couldn’t help myself but this is so much fun.

A new length scale for quantum gravity, Tejinder P. Singh (3 April 2017)

We show why and how Compton wavelength and Schwarzschild radius should be combined into one single new length scale, which we call the Compton-Schwarzschild length. Doing so offers a resolution of the black hole information loss paradox, and suggests Planck mass remnant black holes as candidates for dark matter. It also compels us to introduce torsion, and identify the Dirac field with a complex torsion field. Dirac equation, and Einstein equations, are shown to be mutually dual limiting cases of an underlying gravitation theory which involves the Compton-Schwarzschild length scale, and includes a complex torsion field.

This was really difficult to wade through but following the references I like it.

I’m not too keen on primordial black holes though.

No Comments

Long Term Geochemical Carbon Cycle and Radiative Forcing

by Tommy on 5/04/2017

This is certainly worth reading, just for the weathering stuff.

Future climate forcing potentially without precedent in the last 420 million years, Gavin L. Foster, Dana L. Royer and Daniel J. Lunt, Nature Communications 8, 14845 (4 April 2017), doi:10.1038/ncomms14845

The evolution of Earth’s climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow ∼ 50 Wm−2 increase in TSI over the last ∼ 420 million years (an increase of ∼9 Wm−2 of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO2. This was likely due to the silicate weathering-negative feedback and the expansion of land plants that together ensured Earth’s long-term habitability. Humanity’s fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO2 not seen since the early Eocene (50 million years ago). If CO2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.

It’s official. Again. We’re screwed.

Happy 420 Day! Last Call.

No Comments

Chiral Axial Gravitational Anomaly Found in a Weyl Semimetal

by Tommy on 3/04/2017

And here it is!

Experimental signatures of the mixed axial-gravitational anomaly in the Weyl semimetal NbP, Johannes Gooth, Anna Corinna Niemann, Tobias Meng, Adolfo G. Grushin, Karl Landsteiner, Bernd Gotsmann, Fabian Menges, Marcus Schmidt, Chandra Shekhar, Vicky Sueß, Ruben Huehne, Bernd Rellinghaus, Claudia Felser, Binghai Yan and Kornelius Nielsch (29 March 2017)

Weyl semimetals are materials where electrons behave effectively as a kind of massless relativistic particles known as Weyl fermions. These particles occur in two flavours, or chiralities, and are subject to quantum anomalies, the breaking of a conservation law by quantum fluctuations. For instance, the number of Weyl fermions of each chirality is not independently conserved in parallel electric and magnetic field, a phenomenon known as the chiral anomaly. In addition, an underlying curved spacetime provides a distinct contribution to a chiral imbalance, an effect known as the mixed axial-gravitational anomaly, which remains experimentally elusive. However, the presence of a mixed gauge-gravitational anomaly has recently been tied to thermoelectrical transport in a magnetic field, even in flat spacetime, opening the door to experimentally probe such type of anomalies in Weyl semimetals. Using a temperature gradient, we experimentally observe a positive longitudinal magnetothermoelectric conductance (PMTC) in the Weyl semimetal NbP for collinear temperature gradients and magnetic fields (DT || B) that vanishes in the ultra quantum limit. This observation is consistent with the presence of a mixed axial-gravitational anomaly. Our work provides clear experimental evidence for the existence of a mixed axial-gravitational anomaly of Weyl fermions, an outstanding theoretical concept that has so far eluded experimental detection.

Some vindication is always nice.

No Comments

Cosmic Web Void Structure Evolution Mimics Dark Energy

by Tommy on 1/04/2017

I finally got around to getting up to date on the dark energy controversy.

Concordance cosmology without dark energy, Gábor Rácz, László Dobos, Róbert Beck, István Szapudi and István Csabai, Monthly Notices of the Royal Astromical Society Letters slx026 (12 February 2017), DOI:10.1093/mnrasl/slx026

According to the separate universe conjecture, spherically symmetric sub-regions in an isotropic universe behave like mini-universes with their own cosmological parameters. This is an excellent approximation in both Newtonian and general relativistic theories. We estimate local expansion rates for a large number of such regions, and use a scale parameter calculated from the volume-averaged increments of local scale parameters at each time step in an otherwise standard cosmological N-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This mean field approximation neglects tidal forces and boundary effects, but it is the first step towards a non-perturbative statistical estimation of the effect of non-linear evolution of structure on the expansion rate. Using our algorithm, a simulation with an initial Ωm = 1 Einstein-de~Sitter setting closely tracks the expansion and structure growth history of the ΛCDM cosmology. Due to small but characteristic differences, our model can be distinguished from the ΛCDM model by future precision observations. Moreover, our model can resolve the emerging tension between local Hubble constant measurements and the Planck best-fitting cosmology. Further improvements to the simulation are necessary to investigate light propagation and confirm full consistency with cosmic microwave background observations.

This has been out there for a while, but better late than never!

Update: ESA Euclid Consortium Mission

Euclid Consortium – A Space Mission to Map the Dark Universe

No Comments

The QCD Axion Stabilizes the Higgs Electroweak Vacuum

by Tommy on 31/03/2017

This exposition has been extremely helpful.

The QCD Axion and Electroweak Vacuum Stability, J. McDonald (14 March 2017)

The complex field Φ containing the QCD axion has a natural portal coupling to the Higgs doublet of the form λ |Φ|2 |H|2. Here we consider the possibility that λ has a natural magnitude for a dimensionless coupling, λ ∼ 0.1 − 1. This is possible if the total mass squared parameter of the Higgs in the vacuum, including quadratic divergent and the Φ vacuum expectation value contributions, is renormalized to reproduce the observed Higgs boson mass. It is then possible for the axion sector to stabilize the electroweak vacuum. We show the requirement of electroweak vacuum stability implies that the axion decay constant satisfies fa < 1.3 × 1010 GeV.

I want more of this.

No Comments

Calcium Ruthenate Ca2RuO4 Comes of Age

by Tommy on 30/03/2017

I have questions. I want answers.

Observation of localized high-Tc superconductivity in a Ca2RuO4 nanofilm single crystal, Hiroyoshi Nobukane, Kosei Yanagihara, Yuji Kunisada, Yunito Ogasawara, Kazushige Nomura, Yasuhiro Asano and Satoshi Tanda (28 March 2017)

We report two-dimensional superconducting phase fluctuations in a Ca2RuO4 nanofilm single crystal. A thin film of Ca2RuO4 exhibits typical Kosterlitz-Thouless transition behaviour around TKT = 30 K. We also found that the bias current applied to the thin film causes a superconducotor-insulator transition at low temperatures. The film is superconductive for small bias currents and insulating for large bias currents. The two phases are well separated by the critical sheet resistance of the thin film 16.5 kΩ. In addition to these findings, our results suggest the presence of superconducting fluctuations at a high temperature T = 96 K with onset. The fabrication of nanofilms made of layered material enables us to discuss rich superconducting phenomena in ruthenates.

Sr2RuO4 is already super interesting.

And contentious! That’s always fun.

See also: a penetrating neutron spectroscopy study of this system.

Magnon dispersion in Ca2RuO4: impact of spin-orbit coupling and oxygen moments, S. Kunkemöller, E. Komleva, S. V. Streltsov, S. Hoffmann, D. I. Khomskii, P. Steffens, Y. Sidis, K. Schmalzl and M. Braden (29 March 2017)

The magnon dispersion of Ca2RuO4 has been studied by polarized and unpolarized neutron scattering experiments on crystals containing 0, 1 and 10 % of Ti. The entire dispersion of transverse magnons can be well described by a conventional spin-wave model with interaction and anisotropy parameters that agree with density functional theory calculations. Spin-orbit coupling strongly influences the magnetic excitations, which is most visible in large energies of the magnetic zone-center modes arising from magnetic anisotropy. We find evidence for a low-lying additional mode that exhibits strongest scattering intensity near the antiferromagnetic zone center. This extra signal can be explained by a sizable magnetic moment of 0.11 Bohr magnetons on the apical oxygens parallel to the Ru moment, which is found in the density functional theory calculations. The energy and the signal strength of the additional branch are well described by taking into account this oxygen moment with weak ferromagnetic coupling between Ru and O moments.

No Comments

Possible Alkali Doped Organic Polymer Chain Superconductivity

by Tommy on 22/03/2017

I don’t know what to make of this, but potassium sounds about right for this kind of thing.

Superconductivity above 120 kelvin in a chain link molecule, Ren-Shu Wang, Yun Gao, Zhong-Bing Huang and Xiao-Jia Chen (20 March 2017)

The search for new superconducting compounds with higher critical temperatures Tcs has long been the very heart of scientific research on superconductivity. It took 75 years for scientists to push the Tc above liquid nitrogen boiling temperature since the discovery of superconductivity. So far, the record high Tc of about 130 K at atmosphere pressure was reported in some multilayer Hg(Tl)-Ba-Ca-Cu-O compounds. Meanwhile, sulfur hydride system holds the highest Tc of around 200 K at high pressure of about 150 GPa. While keeping these records for superconductivity, either the toxicity of these superconductors or the requirement of extreme pressure condition for superconductivity limits their technology applications. Here we show that doping a chain link molecule − p-terphenyl by potassium can bring about superconductivity at 123 K at atmosphere pressure, which is comparable to the highest Tc in cuprates. The easy processability, light weight, durability of plastics, and environmental friendliness of this kind of new superconductor have great potential for the fine-tuning of electrical properties. This study opens a window for exploring high temperature superconductivity in chain link organic molecules.

See also:

Superconductivity at 43 K in a single C-C bond linked terphenyl, Ren-Shu Wang, Yun Gao, Zhong-Bing Huang and Xiao-Jia Chen (16 March 2017)

Organic compounds are promising candidates to exhibit high temperature or room temperature superconductivity. However, the critical temperatures of organic superconductors are bounded to 38 K. By doping potassium into p-terphenyl consisting of C and H elements with three phenyl rings connected by single C-C bond in para position, we find that this material can have a superconducting phase with the critical temperature of 43 K. The superconducting parameters such as the critical fields, coherent length, and penetration depth are obtained for this superconductor. These findings open an encouraging window for the search of high temperature superconductors in chain link organic molecules.

From now on I’m only covering the Arxiv on Tuesdays. I was a bipolaron man way back.

I haven’t dabbled too much into it lately. Some of the more extreme bipolaron theories are occasionally considered crackpot, or at least historically so. Here, density counts.

I will have to take it at face value.

No Comments

Remarkable Two Dimensional Amorphized Graphene Produced

by Tommy on 21/03/2017

First there is amorphized bismuth iodide, now it’s amorphized graphene sheets.

The world of condensed matter physics is about to get a lot more exciting. Real soon now!

Amorphized graphene: A stiff material with low thermal conductivity, B Mortazavi, Z Fan, LFC Pereira, A Harju and T Rabczuk (17 March 2017), doi:10.1016/j.carbon.2016.03.007

All-carbon heterostructures have been produced recently via focused ion beam patterning of single layer graphene. Amorphized graphene is similar to a graphene sheet in which some hexagons are replaced by a combination of pentagonal, heptagonal and octagonal rings. The present investigation provides a general view regarding phonon and load transfer along amorphous graphene. The developed models for the evaluation of mechanical and thermal conductivity properties yield accurate results for pristine graphene and acquired findings for amorphized graphene films are size independent. Our atomistic results show that amorphous graphene sheets could exhibit a remarkably high elastic modulus of ~ 500 GPa and tensile strengths of ~ 50 GPa at room temperature. However, our results show that mechanical properties of amorphous graphene decline at higher temperatures. Furthermore, we show that amorphized graphene present a low thermal conductivity ~ 15 W/mK which is two orders of magnitude smaller than pristine graphene, and we verify that its thermal conductivity is almost insensitive to temperature since it is dominated by phonon-defect scattering rather than phonon-phonon scattering. Finally, our results show that amorphized graphene structures present a remarkably high elastic modulus and mechanical strength, along with a low thermal conductivity, which is an unusual combination for carbon-based materials.

I guess this has been out for a while, but it’s the first I heard of it!

I’ve only recently become interested in amorphization.

They just bumped it up to the Arxiv.

A sure way to boost readership.

No Comments

Spectral Weight Distributions in Superconducting Condensates

by Tommy on 21/03/2017

This is something I’ve known for a long time, but now it’s official.

Coexistence of non-Fermi liquid and Fermi liquid self-energies at all dopings in cuprates, Sujay Ray and Tanmoy Das (18 March 2017)

Non-Fermi liquid (NFL) state represents an ensemble of incoherent quantum fluids arising from the coupling between electrons and massless (critical) excitations, and is separated by phase boundary from the quasiparticle behavior in the Fermi-liquid (FL) theory. Here we show that such sharp distinction breaks down in cuprates, and that both NFL and FL states coexists in different momentum (k) regions at all dopings. Their coexistence originates from the strong anisotropy in the many-body self-energy, arising from dispersive density-density fluctuations. The self-energy attains maxima (NFL-like) in the region where density degeneracy is optimum (antinodal region), while the nodal region remains FL-like at all dopings. We attribute the global NFL/FL behavior via the calculation of the resistivity-temperature exponent (n). Surprisingly, we find that the entire Brillouin zone becomes neither fully incoherent, NFL-like even at optimal doping with n = 1, nor fully FL-like even at overdoping (n = 2). As density degeneracy increases in different materials with increasing superconducting Tc, n decreases; providing a microscopic explanation to this intriguing relationship. All results, including coexistence of NFL- and FL-self-energies in the k-space, and their doping, materials dependencies are compared with available experimental data, followed by definite predictions for future studies.

No Comments

Early Galaxy Formation Contrary to Conventional Dark Matter

by Tommy on 15/03/2017

Just when I start thinking deeply and critically about Sabine Hossenfelder’s idea of an inverse baryon anti-correlation of a mass variable gravitational dark matter vector axion boson, deeply tied to universal entropy production and thermodynamic energy balance, there is this result.

Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago, R. Genzel, N. M. Förster Schreiber, H. Übler, P. Lang, T. Naab, R. Bender, L. J. Tacconi, E. Wisnioski, S. Wuyts, T. Alexander, A. Beifiori, S. Belli, G. Brammer, A. Burkert, C. M. Carollo, J. Chan, R. Davies, M. Fossati, A. Galametz, S. Genel, O. Gerhard, D. Lutz, J. T. Mendel, I. Momcheva, E. J. Nelson, A. Renzini, R. Saglia, A. Sternberg, S. Tacchella, K. Tadaki and D. Wilman, Nature 543, 397–401 (16 March 2017), doi:10.1038/nature21685

In the cold dark matter cosmology, the baryonic components of galaxies — stars and gas — are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius — a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

See also:

The evolution of the Tully-Fisher relation between z ∼ 2.3 and z ∼ 0.9 with KMOS3D, H. Übler, N.M. Förster Schreiber, R. Genzel, E. Wisnioski, S. Wuyts, P. Lang, T. Naab, D.J. Wilman, M. Fossati, J.T. Mendel, A. Beifiori, S. Belli, R. Bender, G. Brammer, A. Burkert, J. Chan, R. Davies, M. Fabricius, A. Galametz, D. Lutz, I. Momcheva, E.J. Nelson, R.P. Saglia, S. Seitz, L.J. Tacconi, K. Tadaki and P.G. van Dokkum, Submitted to ApJ (13 March 2017)

We investigate the stellar mass and baryonic mass Tully-Fisher relations (TFRs) of massive star-forming disk galaxies at redshift z ∼ 2.3 and z ∼ 0.9 as part of the KMOS3D integral field spectroscopy survey. Our spatially resolved data allow reliable modelling of individual galaxies, including the effect of pressure support on the inferred gravitational potential. At fixed circular velocity, we find higher baryonic masses and similar stellar masses at z ∼ 2.3 as compared to z ∼ 0.9. Together with the decreasing gas-to-stellar mass ratios with decreasing redshift, this implies that the contribution of dark matter to the dynamical mass at the galaxy scale increases towards lower redshift. A comparison to local relations reveals a negative evolution of the stellar and baryonic TFR zero-points from z = 0 to z ∼ 0.9, no evolution of the stellar TFR zero-point from z ∼ 0.9 to z ∼ 2.3, but a positive evolution of the baryonic TFR zero-point from z ∼ 0.9 to z ∼ 2.3. We discuss a toy model of disk galaxy evolution to explain the observed, non-monotonic TFR evolution, taking into account the empirically motivated redshift dependencies of galactic gas fractions, and of the relative amount of baryons to dark matter on the galaxy and halo scales.

See also also:

Falling outer rotation curves of star-forming galaxies at 0.6 < z < 2.6 probed with KMOS3D and SINS/ZC-SINF, P. Lang, N.M. Förster Schreiber, R. Genzel, S. Wuyts, E. Wisnioski, A. Beifiori, S. Belli, R. Bender, G. Brammer, A. Burkert, J. Chan, R. Davies, M. Fossati, A. Galametz, S.K. Kulkarni, D. Lutz, J.T. Mendel, I.G. Momcheva, T. Naab, E.J. Nelson, R.P. Saglia, S. Seitz, S. Tacchella, L.J. Tacconi, K. Tadaki, H. Übler, P.G. van Dokkum and D.J. Wilman, Submitted to the Astrophysical Journal (16 March 2017)

We exploit the deep resolved Halpha kinematic data from the KMOS3D and SINS/zC-SINF surveys to examine the largely unexplored outer disk kinematics of star-forming galaxies (SFGs) out to the peak of cosmic star formation. Our sample contains 101 SFGs representative of the more massive (9.3 < log(M*/Msun) < 11.5) main sequence population at 0.6 < z < 2.6. Through a novel stacking approach we are able to constrain a representative rotation curve extending out to ~ 4 effective radii. This average rotation curve exhibits a significant drop in rotation velocity beyond the turnover, with a slope of Delta(V)/Delta(R) = −0.26+0.10−0.09 in units of normalized coordinates V/Vmax and R/Rturn. This result confirms that the fall-off seen previously in some individual galaxies is a common feature of our sample of high-z disks. We show that this outer fall-off strikingly deviates from the flat or mildly rising rotation curves of local spiral galaxies of similar masses. We furthermore compare our data with models including baryons and dark matter demonstrating that the falling stacked rotation curve can be explained by a high mass fraction of baryons relative to the total dark matter halo (md > ~ 0.05) in combination with a sizeable level of pressure support in the outer disk. These findings are in agreement with recent studies demonstrating that star-forming disks at high redshift are strongly baryon dominated within the disk scale, and furthermore suggest that pressure gradients caused by large turbulent gas motions are present even in their outer disks. We demonstrate that these results are largely independent of our model assumptions such as the presence of a central stellar bulge, the effect of adiabatic contraction at fixed md, and variations in the concentration parameter.

My gravitational axions are looking better all the time.

No Comments

Pressure Induced Topological Superconductivity of BiTeI Probed

by Tommy on 15/03/2017

Now that both Bi4I4 and BiTeI have been demonstrated to be unusual pressure induced topological superconductors, it would make sense to probe both of them more deeply with modern spectroscopic and ab initio analytical techniques. And it turns out that objective has already been performed on BiTeI.

Superconductivity Bordering Rashba Type Topological Transition, M. L. Jin, F. Sun, L. Y. Xing, S. J. Zhang, S. M. Feng, P. P. Kong, W. M. Li, X. C. Wang, J. L. Zhu, Y. W. Long, H. Y. Bai, C. Z. Gu, R. C. Yu, W. G. Yang, G. Y. Shen, Y. S. Zhao, H. K. Mao and C. Q. Jin, Scientific Reports 7, 39699 (4 January 2017), doi:10.1038/srep39699

Strong spin orbital interaction (SOI) can induce unique quantum phenomena such as topological insulators, the Rashba effect, or p-wave superconductivity. Combining these three quantum phenomena into a single compound has important scientific implications. Here we report experimental observations of consecutive quantum phase transitions from a Rashba type topological trivial phase to topological insulator state then further proceeding to superconductivity in a SOI compound BiTeI tuned via pressures. The electrical resistivity measurement with V shape change signals the transition from a Rashba type topological trivial to a topological insulator phase at 2 GPa, which is caused by an energy gap close then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature TC of 5.3 K. Structure refinements indicate that the consecutive phase transitions are correlated to the changes in the Bi–Te bond and bond angle as function of pressures. The Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity.

Next up, Bi4I4.

No Comments

Record Breaking Weyl Semimetal Tungsten Diphosphide – WP2

by Tommy on 14/03/2017

It’s something new every day, for the guy who utterly failed to predict the iron arsenides in 1994.

Extremely high magnetoresistance and conductivity in the type-II Weyl semimetal WP2, Nitesh Kumar, Yan Sun, Kaustuv Manna, Vicky Suess, Inge Leermakers, Olga Young, Tobias Foerster, Marcus Schmidt, Binghai Yan, Uli Zeitler, Claudia Felser and Chandra Shekhar (13 March 2017)

The experimental realization of tungsten diphosphide, WP2, a type-II Weyl semimetal with robust Weyl points is presented. Weyl points are closely located to each other in the Brillouin zone but here are of the same chirality and are therefore protected against annihilation from structural distortions or defects. The single crystals show extremely high residual resistivity (RRR) values of 25,000 with a very low residual resistivity of 3 nano-ohm cm, and an enormous, highly anisotropic, magnetoresistance that exceeds 200 million percent at 63 T and 0.5 K. These properties are likely a consequence of the novel fermions expressed in this compound.

I did point out that any metal-insulator sitting across the metalloid band would be cool, though.

In this case, very cool.

No Comments

I’m an American. I Love America, Don’t Let Me Down.

by Tommy on 12/03/2017

March 20, 2017, on CSPAN.

Be there or be square.

Update: Happy Pi Day!

No Comments

Sabine Hossenfelder Discovers a Vector Axion Condensate

by Tommy on 12/03/2017

Sort of. I haven’t really had time to work through the math yet.

But this is promising that axions may indeed be gravitational.

Or alternatively that gravitational spacetime may be emergent.

I sense a duality in progress. That means a song may be coming on!

Is Verlinde’s Emergent Gravity compatible with General Relativity?

A Covariant Version of Verlinde’s Emergent Gravity, Sabine Hossenfelder (4 March 2017)

A generally covariant version of Erik Verlinde’s emergent gravity model is proposed. The Lagrangian constructed here allows an improved interpretation of the underlying mechanism. It suggests that de-Sitter space is filled with a vector-field that couples to baryonic matter and, by dragging on it, creates an effect similar to dark matter. We solve the covariant equation of motion in the background of a Schwarzschild space-time and obtain correction terms to the non-covariant expression. Furthermore, we demonstrate that the vector field can also mimic dark energy.

No Comments

Higgs Amplitude Modes, Goldstone Modes, Pair Density Waves

by Tommy on 9/03/2017

And of course Eduardo Fradkin et al., at the University of Illinois Urbana-Champaign rocks.

Check out this study. They’re doing quantum cosmology and they don’t even know it!

Higgs Modes in the Pair Density Wave Superconducting State, Rodrigo Soto-Garrido, Yuxuan Wang, Eduardo Fradkin and S. Lance Cooper (7 March 2017)

The pair density wave (PDW) superconducting state has been proposed to explain the layer- decoupling effect observed in the compound La2−xBaxCuO4 at x = 1/8 (Phys. Rev. Lett. 99, 127003). In this state the superconducting order parameter is spatially modulated, in contrast with the usual superconducting (SC) state where the order parameter is uniform. In this work, we study the properties of the amplitude (Higgs) modes in a unidirectional PDW state. To this end we consider a phenomenological model of PDW type states coupled to a Fermi surface of fermionic quasiparticles. In contrast to conventional superconductors that have a single Higgs mode, unidirectional PDW superconductors have two Higgs modes. While in the PDW state the Fermi surface largely remains gapless, we find that the damping of the PDW Higgs modes into fermionic quasiparticles requires exceeding an energy threshold. We show that this suppression of damping in the PDW state is due to kinematics. As a result, only one of the two Higgs modes is significantly damped. In addition, motivated by the experimental phase diagram, we discuss the mixing of Higgs modes in the coexistence regime of the PDW and uniform SC states. These results should be observable directly in a Raman spectroscopy, in momentum resolved electron energy loss spectroscopy, and in resonant inelastic X-ray scattering, thus providing evidence of the PDW states.

You need to read this paper because this is as good as it gets nowadays.

No Comments