608 research outputs found
Spinon Phonon Interaction and Ultrasonic Attenuation in Quantum Spin Liquids
Several experimental candidates for quantum spin liquids have been discovered
in the past few years which appear to support gapless fermionic excitations called spinons. The spinons may form a Fermi sea coupled to a
gauge field, and may undergo a pairing instability. We show that despite
being charge neutral, the spinons couple to phonons in exactly the same way
that electrons do in the long wavelength limit. Therefore we can use sound
attenuation to measure the spinon mass and lifetime. Furthermore, transverse
ultrasonic attenuation is a direct probe of the onset of pairing because the
Meissner effect of the gauge field causes a "rapid fall" of the attenuation at
in addition to the reduction due to the opening of the energy gap. This
phenomenon, well known in clean superconductors, may reveal the existence of
the U(1) gauge field.Comment: 4+epsilon pages of main text + 12 pages of supplementary materia
Low- Phononic Thermal Conductivity in Superconductors with Line Nodes
The phonon contribution to the thermal conductivity at low temperature in
superconductors with line nodes is calculated assuming that scattering by both
nodal quasiparticles and the sample boundaries is significant. It is determined
that, within the regime in which the quasiparticles are in the universal limit
and the phonon attenuation is in the hydrodynamic limit, there exists a wide
temperature range over which the phonon thermal conductivity varies as .
This behaviour comes from the fact that transverse phonons propagating along
certain directions do not interact with nodal quasiparticles and is thus found
to be required by the symmetry of the crystal and the superconducting gap,
independent of the model used for the electron-phonon interaction. The
-dependence of the phonon thermal conductivity occurs over a well-defined
intermediate temperature range: at higher the temperature-dependence is
found to be linear while at lower the usual (boundary-limited)
behaviour is recovered. Results are compared to recent measurements of the
thermal conductivity of Tl2201, and are shown to be consistent with the data.Comment: 4 page
An analytical treatment of in-plane magnetotransport in the Falicov-Sievert model
We derive an analytical expression which allows efficient computation of the
effect of all the Fermi surface trajectories induced by a combination of Bragg
scattering and magnetic breakdown on the in-plane components of the resistivity
tensor. The particular network of coupled orbits which we consider was first
formulated by Falicov and Sievert, who studied the problem numerically. Our
approach, based upon a method used previously to derive an analytical solution
for interlayer transport, allows us to show that the conductivity tensor can be
written as a sum of a matrix representing the effect of total magnetic
breakdown and one representing a combination of complex electronic
trajectories, and we find a compact expression for the in-plane components of
the resistivity tensor that can be evaluated straightforwardly.Comment: 4 pages, 4 figure
Intervalley-Scattering Induced Electron-Phonon Energy Relaxation in Many-Valley Semiconductors at Low Temperatures
We report on the effect of elastic intervalley scattering on the energy
transport between electrons and phonons in many-valley semiconductors. We
derive a general expression for the electron-phonon energy flow rate at the
limit where elastic intervalley scattering dominates over diffusion. Electron
heating experiments on heavily doped n-type Si samples with electron
concentration in the range m are performed at
sub-1 K temperatures. We find a good agreement between the theory and the
experiment.Comment: v2: Notations changed: --> ,
removed. Eq. (1) changed, Eq. (2) added and complete derivation of Eq. (3)
included. Some further discussion about single vs. many valley added [3rd
paragraph after Eq. (7)]. End notes removed and new reference added [Kragler
and Thomas]. Typos in references correcte
The effect of Aharanov-Bohm phase on the magnetic-field dependence of two-pulse echos in glasses at low temperatures
The anomalous response of glasses in the echo amplitude experiment is
explained in the presence of a magnetic field. We have considered the low
energy excitations in terms of an effective two level system. The effective
model is constructed on the flip-flop configuration of two interacting two
level systems. The magnetic field affects the tunneling amplitude through the
Aharanov-Bohm effect. The effective model has a lower scale of energy in
addition to the new distribution of tunneling parameters which depend on the
interaction. We are able to explain some features of echo amplitude versus a
magnetic field, namely, the dephasing effect at low magnetic fields, dependence
on the strength of the electric field, pulse separation effect and the
influence of temperature. However this model fails to explain the isotope
effects which essentially can be explained by the nuclear quadrupole moment. We
will finally discuss the features of our results.Comment: 8 pages, 7 figure
Breakdown of weak-field magnetotransport at a metallic quantum critical point
We show how the collapse of an energy scale in a quantum critical metal can
lead to physics beyond the weak-field limit usually used to compute transport
quantities. For a density-wave transition we show that the presence of a finite
magnetic field at the critical point leads to discontinuities in the transport
coefficients as temperature tends to zero. The origin of these discontinuities
lies in the breakdown of the weak field Jones-Zener expansion which has
previously been used to argue that magneto-transport coefficients are
continuous at simple quantum critical points. The presence of potential
scattering and magnetic breakdown rounds the discontinuities over a window
determined by tau Delta < 1 where Delta is the order parameter and tau is the
quasiparticle elastic lifetime.Comment: 4 pages, 3 figures RevTeX forma
Clausius inequality and optimality of quasi static transformations for nonequilibrium stationary states
Nonequilibrium stationary states of thermodynamic systems dissipate a
positive amount of energy per unit of time. If we consider transformations of
such states that are realized by letting the driving depend on time, the amount
of energy dissipated in an unbounded time window becomes then infinite.
Following the general proposal by Oono and Paniconi and using results of the
macroscopic fluctuation theory, we give a natural definition of a renormalized
work performed along any given transformation. We then show that the
renormalized work satisfies a Clausius inequality and prove that equality is
achieved for very slow transformations, that is in the quasi static limit. We
finally connect the renormalized work to the quasi potential of the macroscopic
fluctuation theory, that gives the probability of fluctuations in the
stationary nonequilibrium ensemble
Multiorbital effects on the transport and the superconducting fluctuations in LiFeAs
The resistivity, Hall effect and transverse magnetoresistance (MR) have been
measured in low residual resistivity single crystals of LiFeAs. A comparison
with angle resolved photoemission spectroscopy and quantum oscillation data
implies that four carrier bands unevenly contribute to the transport. However
the scattering rates of the carriers all display the T^2 behavior expected for
a Fermi liquid. Near Tc low field deviations of the MR with respect to a H^2
variation permit us to extract the superconducting fluctuation contribution to
the conductivity. Though below Tc the anisotropy of superconductivity is rather
small, the superconducting fluctuations display a quasi ideal two-dimensional
behavior which persists up to 1.4 Tc. These results call for a refined
theoretical understanding of the multiband behavior of superconductivity in
this pnictide.Comment: 8pages with supplementary material, 6 figure
Analytical treatment of the dHvA frequency combinations due to chemical potential oscillations in an idealized two-band Fermi liquid
de Haas-van Alphen oscillation spectrum is studied for an idealized
two-dimensional Fermi liquid with two parabolic bands in the case of canonical
(fixed number of quasiparticles) and grand canonical (fixed chemical potential)
ensembles. As already reported in the literature, oscillations of the chemical
potential in magnetic field yield frequency combinations that are forbidden in
the framework of the semiclassical theory. Exact analytical calculation of the
Fourier components is derived at zero temperature and an asymptotic expansion
is given for the high temperature and low magnetic field range. A good
agreement is obtained between analytical formulae and numerical computations.Comment: 10 pages, 4 figure
Weak- to strong pinning crossover
Material defects in hard type II superconductors pin the flux lines and thus
establish the dissipation-free current transport in the presence of a finite
magnetic field. Depending on the density and pinning force of the defects and
the vortex density, pinning is either weak-collective or strong. We analyze the
weak- to strong pinning crossover of vortex matter in disordered
superconductors and discuss the peak effect appearing naturally in this
context.Comment: 4 pages, 2 figure
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