13,007 research outputs found
Nernst Effect as a Probe of Local Kondo Scattering in Heavy Fermions
A large, strongly temperature-dependent Nernst coefficient, , is
observed between = 2 K and 300 K for CeCuSi and
CeLaCuSi. The enhanced is determined by the
asymmetry of the on-site Kondo (conduction electron electron) scattering
rate. Taking into account the measured Hall mobility, , the highly
unusual thermopower, , of these systems can be semiquantitatively described
by , which explicitly demonstrates that the
thermopower originates from the local Kondo scattering process over a wide
temperature range from far above to well below the coherence temperature
( 20 K for CeCuSi). Our results suggest that the Nernst effect
can act as a proper probe of local charge-carrier scattering. This promises an
impact on exploring the unconventional enhancement of the thermopower in
correlated materials suited for potential applications.Comment: 10 pages, 2 Figure
Guaranteed bounds on the Kullback-Leibler divergence of univariate mixtures using piecewise log-sum-exp inequalities
Information-theoretic measures such as the entropy, cross-entropy and the
Kullback-Leibler divergence between two mixture models is a core primitive in
many signal processing tasks. Since the Kullback-Leibler divergence of mixtures
provably does not admit a closed-form formula, it is in practice either
estimated using costly Monte-Carlo stochastic integration, approximated, or
bounded using various techniques. We present a fast and generic method that
builds algorithmically closed-form lower and upper bounds on the entropy, the
cross-entropy and the Kullback-Leibler divergence of mixtures. We illustrate
the versatile method by reporting on our experiments for approximating the
Kullback-Leibler divergence between univariate exponential mixtures, Gaussian
mixtures, Rayleigh mixtures, and Gamma mixtures.Comment: 20 pages, 3 figure
Resonant Charge Relaxation as a Likely Source of the Enhanced Thermopower in FeSi
The enhanced thermopower of the correlated semiconductor FeSi is found to be
robust against the sign of the relevant charge carriers. At \,\,70
K, the position of both the high-temperature shoulder of the thermopower peak
and the nonmagnetic-enhanced paramagnetic crossover, the Nernst coefficient
assumes a large maximum and the Hall mobility diminishes to
below 1 cm/Vs. These cause the dimension-less ratio / a
measure of the energy dispersion of the charge scattering time
to exceed that of classical metals and semiconductors by two orders of
magnitude. Concomitantly, the resistivity exhibits a hump and the
magnetoresistance changes its sign. Our observations hint at a resonant
scattering of the charge carriers at the magnetic crossover, imposing strong
constraints on the microscopic interpretation of the robust thermopower
enhancement in FeSi.Comment: 5 pages, 3 figure
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