351 research outputs found
Interaction corrections: temperature and parallel field dependencies of the Lorentz number in two-dimensional disordered metals
The electron-electron interaction corrections to the transport coefficients
are calculated for a two-dimensional disordered metal in a parallel magnetic
field via the quantum kinetic equation approach. For the thermal transport,
three regimes (diffusive, quasiballistic and truly ballistic) can be identified
as the temperature increases. For the diffusive and quasiballistic regimes, the
Lorentz number dependence on the temperature and on the magnetic field is
studied. The electron-electron interactions induce deviations from the
Wiedemann-Franz law, whose sign depend on the temperature: at low temperatures
the long-range part of the Coulomb interaction gives a positive correction,
while at higher temperature the inelastic collisions dominate the negative
correction. By applying a parallel field, the Lorentz number becomes a
non-monotonic function of field and temperature for all values of the
Fermi-liquid interaction parameter in the diffusive regime, while in the
quasiballistic case this is true only sufficiently far from the Stoner
instability.Comment: 11 pages, 5 figures. Appendix A revised, notes adde
Quantum spin liquids and the metal-insulator transition in doped semiconductors
We describe a new possible route to the metal-insulator transition in doped
semiconductors such as Si:P or Si:B. We explore the possibility that the loss
of metallic transport occurs through Mott localization of electrons into a
quantum spin liquid state with diffusive charge neutral "spinon" excitations.
Such a quantum spin liquid state can appear as an intermediate phase between
the metal and the Anderson-Mott insulator. An immediate testable consequence is
the presence of metallic thermal conductivity at low temperature in the
electrical insulator near the metal-insulator transition. Further we show that
though the transition is second order the zero temperature residual electrical
conductivity will jump as the transition is approached from the metallic side.
However the electrical conductivity will have a non-monotonic temperature
dependence that may complicate the extrapolation to zero temperature.
Signatures in other experiments and some comparisons with existing data are
made.Comment: 4 pages text + 3 pages Appendices, 3 Figures; v2 - References Adde
Electron-electron interaction corrections to the thermal conductivity in disordered conductors
We evaluate the electron-electron interaction corrections to the electronic
thermal conductivity in a disordered conductor in the diffusive regime. We use
a diagrammatic many-body method analogous to that of Altshuler and Aronov for
the electrical conductivity. We derive results in one, two and three dimensions
for both the singlet and triplet channels, and in all cases find that the
Wiedemann-Franz law is violated.Comment: 8 pages, 2 figures Typos corrected in formulas (15) and (A.4) and
Table 1; discussion of previous work in introduction extended; reference
clarifying different definitions of parameter F adde
Field-Dependent Hall Effect in Single Crystal Heavy Fermion YbAgGe below 1K
We report the results of a low temperature (T >= 50 mK) and high field (H <=
180 kOe) study of the Hall resistivity in single crystals of YbAgGe, a heavy
fermion compound that demonstrates field-induced non-Fermi-liquid behavior near
its field-induced quantum critical point. Distinct features in the anisotropic,
field-dependent Hall resistivity sharpen on cooling down and at the base
temperature are close to the respective critical fields for the field-induced
quantum critical point. The field range of the non-Fermi-liquid region
decreases on cooling but remains finite at the base temperature with no
indication of its conversion to a point for T -> 0. At the base temperature,
the functional form of the field-dependent Hall coefficient is field direction
dependent and complex beyond existing simple models thus reflecting the
multi-component Fermi surface of the material and its non-trivial modification
at the quantum critical point
Thermal transport in granular metals
We study the electron thermal transport in granular metals at large tunnel
conductance between the grains, and not too low a temperature , where is the mean energy level spacing for a single grain.
Taking into account the electron-electron interaction effects we calculate the
thermal conductivity and show that the Wiedemann-Franz law is violated for
granular metals. We find that interaction effects suppress the thermal
conductivity less than the electrical conductivity.Comment: Replaced with published versio
Optimization and performance of an optical cardio-magnetometer
Cardiomagnetometry is a growing field of noninvasive medical diagnostics that
has triggered a need for affordable high-sensitivity magnetometers. Optical
pumping magnetometers are promising candidates satisfying that need since it
was demonstrated that they can map the heart magnetic field. For the
optimization of such devices theoretical limits on the performance as well as
an experimental approach is presented. The promising result is a intrinsic
magnetometric sensitivity of 63 fT / Hz^1/2 a measurement bandwidth of 140 Hz
and a spatial resolution of 28 mm
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