186 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
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
Enhanced electron correlations in FeSb
FeSb has been recently identified as a new model system for studying
many-body renormalizations in a -electron based narrow gap semiconducting
system, strongly resembling FeSi. The electron-electron correlations in
FeSb manifest themselves in a wide variety of physical properties including
electrical and thermal transport, optical conductivity, magnetic
susceptibility, specific heat and so on. We review some of the properties that
form a set of experimental evidences revealing the crucial role of correlation
effects in FeSb. The metallic state derived from slight Te doping in
FeSb, which has large quasiparticle mass, will also be introduced.Comment: 9 pages, 7 figures; submitted to Annalen der Physi
Physical properties and crystal chemistry of Ce2Ga12Pt
Single crystals of the new ternary compound Ce2Ga12Pt were prepared by the
self-flux technique. The crystal structure with the space group P4/nbm was
established from single-crystal X-ray diffraction data and presents a
derivative of the LaGa6Ni0.6 prototype. Magnetic susceptibility measurements
show Curie-Weiss behaviour due to local Ce^3+ moments. At high temperatures,
the magnetic anisotropy is dominated by the crystal-electric-field (CEF) effect
with the easy axis along the crystallographic c direction. Ce2Ga12Pt undergoes
two antiferromagnetic phase transitions at T_N,1 = 7.3K and T_N,2 = 5.5K and
presents several metamagnetic transitions for the magnetic field along c.
Specific-heat measurements prove the bulk nature of these magnetic transitions
and reveal a doublet CEF ground state. The 4f contribution to the resistivity
shows a broad maximum at T_max ~ 85K due to Kondo scattering off the CEF ground
state and excited levels.Comment: 12 pages, accepted in J. Phys.: Condens. Matte
Magnetization study of the energy scales in YbRhSi under chemical pressure
We present a systematic study of the magnetization in YbRhSi
under slightly negative (6?% Ir substitution) and positive (7% Co substitution)
chemical pressure. We show how the critical field , associated with the
high-field Lifshitz transitions, is shifted to lower (higher) values with Co
(Ir) substitution. The critical field , which identifies the
boundary line of the antiferromagnetic (AFM) phase
increases with positive pressure and it approaches zero with 6% Ir
substitution. On the other side, the crossover field , associated with
the energy scale where a reconstruction of the Fermi surface has
been observed, is not much influenced by the chemical substitution.}{Following
the analysis proposed in
Refs.\,\cite{Paschen2004,Gegenwart2007,Friedemann2009,Tokiwa2009a} we have
fitted the quantity with a crossover function to
indentify . The line follows an almost linear -dependence
at sufficiently high fields outside the AFM phase, but it deviates from
linearity at and in
Yb(RhCo)Si it changes slope clearly inside the
AFM phase. Moreover, the FWHM of the fit function depends linearly on
temperature outside the phase, but remains constant inside, suggesting either
that such an analysis is valid only for or that the
Fermi surface changes continuously at inside the AFM phase.}}Comment: 6 pages, 4 figure
Quantum criticality in Yb(Rh0.97Co0.03)2Si2 probed by low-temperature resistivity
Quantum criticality in Yb(Rh0.97Co0.03)2Si2 is investigated by means of
resistivity and magnetoresistance. The partial substitution of Co leads to a
stabilization of the magnetism as expected according to the application of
chemical pressure for Yb systems. However, the signature of the Kondo-breakdown
remains at the same position in the temperature-magnetic field phase diagram
compared to stoichiometric YbRh2Si2. As a consequence, the Kondo-breakdown is
situated within the antiferromagnetic phase. These results fit well within the
global phase diagram under chemical pressure [1].Comment: 4 pages, 4 figures, submitted to ICM/SCES200
Signatures of phase transitions in the microwave response of YbRh2Si2
We used a spectroscopic microwave technique utilizing superconducting
stripline resonators at frequencies between 3 GHz and 15 GHz to examine the
charge dynamics of YbRh2Si2 at temperatures and magnetic fields close to the
quantum critical point. The different electronic phases of this heavy-fermion
compound, in particular the antiferromagnetic, Fermi-liquid, and
non-Fermi-liquid regimes, were probed with temperature-dependent microwave
measurements between 40 mK and 600 mK at a set of different magnetic fields up
to 140 mT. Signatures of phase transitions were observed, which give
information about the dynamic response of this peculiar material that exhibits
field-tuned quantum criticality and pronounced deviations from Fermi-liquid
theory.Comment: 5 pages, 3 figure
Emergence of an incipient ordering mode in FeSe
The structurally simplest Fe-based superconductor FeSe with a critical
temperature 8.5 K displays a breaking of the four-fold
rotational symmetry at a temperature K. We investigated the
electronic properties of FeSe using scanning tunneling microscopy/spectroscopy
(STM/S), magnetization, and electrical transport measurements. The results
indicated two new energy scales (i) 75 K denoted by an onset of
electron-hole asymmetry in STS, enhanced spin fluctuations, and increased
positive magnetoresistance; (ii) 22 - 30 K, marked by opening
up of a partial gap of about 8 meV in STS and a recovery of Kohler's rule. Our
results reveal onset of an incipient ordering mode at and its
nucleation below . The ordering mode observed here, both in spin as
well as charge channels, suggests a coupling between the spins with charge,
orbital or pocket degrees of freedom.Comment: 5 pages, 4 figure
Highly Dispersive Electron Relaxation and Colossal Thermoelectricity in the Correlated Semiconductor FeSb
We show that the colossal thermoelectric power, , observed in the
correlated semiconductor FeSb below 30\,K is accompanied by a huge Nernst
coefficient and magnetoresistance MR. Markedly, the latter two
quantities are enhanced in a strikingly similar manner. While in the same
temperature range, of the reference compound FeAs, which has a
seven-times larger energy gap, amounts to nearly half of that of FeSb, its
and MR are intrinsically different to FeSb: they are smaller
by two orders of magnitude and have no common features. With the charge
transport of FeAs successfully captured by the density functional theory,
we emphasize a significantly dispersive electron-relaxation time
due to electron-electron correlations to be at the heart of
the peculiar thermoelectricity and magnetoresistance of FeSb.Comment: 8 pages, 5 figure
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