248 research outputs found
Comment on "Terahertz time-domain spectroscopy of transient metallic and superconducting states" (arXiv:1506.06758)
We comment on the model proposed by Orenstein and Dodge in
arXiv:1506.06758v1, which describes time-domain terahertz measurements of
transiently generated, high-electron-mobility (or superconducting) phases of
solids. The authors' main conclusion is that time-domain terahertz spectroscopy
does not measure a response function that is mathematically identical to the
transient optical conductivity. We show that although this is correct, the
difference between the measured response function and the microscopic optical
conductivity is small for realistic experimental parameters. We also show that
for the experiments reported by our group on light-induced superconducting-like
phases in cuprates and in organic conductors, the time-domain terahertz yields
a very good estimate for the optical conductivity.Comment: 3 pages, 1 figure, comment on arXiv:1506.0675
Pressure tuning of light-induced superconductivity in K3C60
Optical excitation at terahertz frequencies has emerged as an effective means
to manipulate complex solids dynamically. In the molecular solid K3C60,
coherent excitation of intramolecular vibrations was shown to transform the
high temperature metal into a non-equilibrium state with the optical
conductivity of a superconductor. Here we tune this effect with hydrostatic
pressure, and we find it to disappear around 0.3 GPa. Reduction with pressure
underscores the similarity with the equilibrium superconducting phase of K3C60,
in which a larger electronic bandwidth is detrimental for pairing. Crucially,
our observation excludes alternative interpretations based on a high-mobility
metallic phase. The pressure dependence also suggests that transient, incipient
superconductivity occurs far above the 150 K hypothesised previously, and
rather extends all the way to room temperature.Comment: 33 pages, 17 figures, 2 table
Assessing a Hydrodynamic Description for Instabilities in Highly Dissipative, Freely Cooling Granular Gases
An intriguing phenomenon displayed by granular flows and predicted by
kinetic-theory-based models is the instability known as particle "clustering,"
which refers to the tendency of dissipative grains to form transient, loose
regions of relatively high concentration. In this work, we assess a
modified-Sonine approximation recently proposed [Garz\'o et al., Physica A 376,
94 (2007)] for a granular gas via an examination of system stability. In
particular, we determine the critical length scale associated with the onset of
two types of instabilities -vortices and clusters- via stability analyses of
the Navier-Stokes-order hydrodynamic equations by using the expressions of the
transport coefficients obtained from both the standard and the modified-Sonine
approximations. We examine the impact of both Sonine approximations over a
range of solids fraction \phi <0.2 for small restitution coefficients
e=0.25--0.4, where the standard and modified theories exhibit discrepancies.
The theoretical predictions for the critical length scales are compared to
molecular dynamics (MD) simulations, of which a small percentage were not
considered due to inelastic collapse. Results show excellent quantitative
agreement between MD and the modified-Sonine theory, while the standard theory
loses accuracy for this highly dissipative parameter space. The modified theory
also remedies a (highdissipation) qualitative mismatch between the standard
theory and MD for the instability that forms more readily. Furthermore, the
evolution of cluster size is briefly examined via MD, indicating that
domain-size clusters may remain stable or halve in size, depending on system
parameters.Comment: 4 figures; to be published in Phys. Rev.
Witnessing nonequilibrium entanglement dynamics in a strongly correlated fermionic chain
Many-body entanglement in condensed matter systems can be diagnosed from equilibrium response functions through the use of entanglement witnesses and operator-specific quantum bounds. Here, we investigate the applicability of this approach for detecting entangled states in quantum systems driven out of equilibrium. We use a multipartite entanglement witness, the quantum Fisher information, to study the dynamics of a paradigmatic fermion chain undergoing a time-dependent change of the Coulomb interaction. Our results show that the quantum Fisher information is able to witness distinct signatures of multipartite entanglement both near and far from equilibrium that are robust against decoherence. We discuss implications of these findings for probing entanglement in light-driven quantum materials with time-resolved optical and x-ray scattering methods
Clustering Instabilities in Gas-Solid Systems: Role of Dissipative Collisions vs. Viscous Losses
Clustering Instabilities in Gas-Solid Systems: Role of Dissipative Collisions vs. Viscous Losses
https://digitalrepository.unm.edu/abq_mj_news/4755/thumbnail.jp
Enhanced electron-phonon coupling in graphene with periodically distorted lattice
Electron-phonon coupling directly determines the stability of cooperative
order in solids, including superconductivity, charge and spin density waves.
Therefore, the ability to enhance or reduce electron-phonon coupling by optical
driving may open up new possibilities to steer materials' functionalities,
potentially at high speeds. Here we explore the response of bilayer graphene to
dynamical modulation of the lattice, achieved by driving optically-active
in-plane bond stretching vibrations with femtosecond mid-infrared pulses. The
driven state is studied by two different ultrafast spectroscopic techniques.
Firstly, TeraHertz time-domain spectroscopy reveals that the Drude scattering
rate decreases upon driving. Secondly, the relaxation rate of hot
quasi-particles, as measured by time- and angle-resolved photoemission
spectroscopy, increases. These two independent observations are quantitatively
consistent with one another and can be explained by a transient three-fold
enhancement of the electron-phonon coupling constant. The findings reported
here provide useful perspective for related experiments, which reported the
enhancement of superconductivity in alkali-doped fullerites when a similar
phonon mode was driven.Comment: 12 pages, 4 figure
Editorial:Exploring the combined effect of climate change and pollution on freshwater ecosystems
ISSN:2296-665
Coexisting Fermi Liquid and Strange Metal Phenomena in SrRuO
The strange metal is an enigmatic phase whose properties are irreconcilable
with the established Fermi liquid theory of conductors. A fundamental question
is whether a strange metal and a Fermi liquid are distinct phases of matter, or
whether a material can be intermediate between or in a superposition of the
two. We studied the collective density response of the correlated metal
SrRuO by momentum-resolved electron energy-loss spectroscopy (M-EELS).
We discovered that a broad continuum of non-propagating charge fluctuations (a
characteristic of strange metals) and also a dispersing Fermi liquid-like
collective mode at low energies and long wavelengths coexist in the same
material at the same temperature. These features exhibit a spectral weight
redistribution and velocity renormalization when we cool the material through
the quasiparticle coherence temperature. Our results show not only that strange
metal and Fermi liquid phenomena can coexist but also that SrRuO serves
as an ideal test case for studying the interaction between the two.Comment: 12 pages, 4 figure
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