462 research outputs found
Nonvanishing Energy Scales at the Quantum Critical Point of CeCoIn5
Heat and charge transport were used to probe the magnetic field-tuned quantum
critical point in the heavy-fermion metal CeCoIn. A comparison of
electrical and thermal resistivities reveals three characteristic energy
scales. A Fermi-liquid regime is observed below , with both transport
coefficients diverging in parallel and as , the
critical field. The characteristic temperature of antiferromagnetic spin
fluctuations, , is tuned to a minimum but {\it finite} value at ,
which coincides with the end of the -linear regime in the electrical
resistivity. A third temperature scale, , signals the formation of
quasiparticles, as fermions of charge obeying the Wiedemann-Franz law.
Unlike , it remains finite at , so that the integrity of
quasiparticles is preserved, even though the standard signature of Fermi-liquid
theory fails.Comment: 4 pages, 4 figures (published version
Influence of a magnetic field on the antiferromagnetic order in UPt_3
A neutron diffraction experiment was performed to investigate the effect of a
magnetic field on the antiferromagnetic order in the heavy fermion
superconductor UPt_3. Our results show that a field in the basal plane of up to
3.2 Tesla, higher than H_c2(0), has no effect: it can neither select a domain
nor rotate the moment. This has a direct impact on current theories for the
superconducting phase diagram based on a coupling to the magnetic order.Comment: 7 pages, RevTeX, 3 postscript figures, submitted to Phys. Rev.
Heat Transport as a Probe of Electron Scattering by Spin Fluctuations: the Case of Antiferromagnetic CeRhIn5
Heat and charge conduction were measured in the heavy-fermion metal CeRhIn5,
an antiferromagnet with T_N=3.8 K. The thermal resistivity is found to be
proportional to the magnetic entropy, revealing that spin fluctuations are as
effective in scattering electrons as they are in disordering local moments. The
electrical resistivity, governed by a q^2 weighting of fluctuations, increases
monotonically with temperature. In contrast, the difference between thermal and
electrical resistivities, characterized by an omega^2 weighting, peaks sharply
at T_N and eventually goes to zero at a temperature T^* ~ 8 K. T^* thus emerges
as a measure of the characteristic energy of magnetic fluctuations.Comment: 4 pages, 4 figure
Two types of nematicity in the phase diagram of the cuprate superconductor YBaCuO
Nematicity has emerged as a key feature of cuprate superconductors, but its
link to other fundamental properties such as superconductivity, charge order
and the pseudogap remains unclear. Here we use measurements of transport
anisotropy in YBaCuO to distinguish two types of nematicity. The
first is associated with short-range charge-density-wave modulations in a
doping region near . It is detected in the Nernst coefficient, but
not in the resistivity. The second type prevails at lower doping, where there
are spin modulations but no charge modulations. In this case, the onset of
in-plane anisotropy - detected in both the Nernst coefficient and the
resistivity - follows a line in the temperature-doping phase diagram that
tracks the pseudogap energy. We discuss two possible scenarios for the latter
nematicity.Comment: 8 pages and 7 figures. Main text and supplementary material now
combined into single articl
Giant electron-electron scattering in the Fermi-liquid state of Na_0.7CoO_2
The in-plane resistivity, rho, and thermal conductivity, kappa, of a single
crystal of Na_0.7CoO_2 were measured down to 40 mK. Verification of the
Wiedemann-Franz law, kappa/T = L_0/rho as T -> 0, and observation of a T^2
dependence of rho at low temperature, rho = rho_0 + AT^2, establish the
existence of a well-defined Fermi-liquid state. The measured value of
coefficient A reveals enormous electron-electron scattering, characterized by
the largest Kadowaki-Woods ratio, A/gamma^2, encountered in any material. The
rapid suppression of A with magnetic field suggests a possible proximity to a
magnetic quantum critical point. We also speculate on the possible role of
magnetic frustration and proximity to a Mott insulator.Comment: 4 pages, 4 figures; replaced with published version; added references
and supporting dat
The Fermi surface and f-valence electron count of UPt3
Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data,
we arrive at a detailed picture of the Fermi surface of the heavy fermion
superconductor UPt3. Our work was partially motivated by a new proposal that
two 5f valence electrons per formula unit in UPt3 are localized by correlation
effects -- agreement with previous dHvA measurements of the Fermi surface was
invoked in its support. Comprehensive comparison with our new observations
shows that this 'partially localized' model fails to predict the existence of a
major sheet of the Fermi surface, and is therefore less compatible with
experiment than the originally proposed 'fully itinerant' model of the
electronic structure of UPt3. In support of this conclusion, we offer a more
complete analysis of the fully itinerant band structure calculation, where we
find a number of previously unrecognized extremal orbits on the Fermi surface.Comment: 23 pages, 12 figures, latex, iopart clas
Field-Induced Quantum Critical Point in CeCoIn5
The resistivity of the heavy-fermion superconductor CeCoIn5 was measured as a
function of temperature, down to 25 mK and in magnetic fields of up to 16 T
applied perpendicular to the basal plane. With increasing field, we observe a
suppression of the non-Fermi liquid behavior, rho ~ T, and the development of a
Fermi liquid state, with its characteristic rho = rho_0 + AT^2 dependence. The
field dependence of the T^2 coefficient shows critical behavior with an
exponent of 1.37. This is evidence for a field-induced quantum critical point
(QCP), occuring at a critical field which coincides, within experimental
accuracy, with the superconducting critical field H_c2. We discuss the relation
of this field-tuned QCP to a change in the magnetic state, seen as a change in
magnetoresistance from positive to negative, at a crossover line that has a
common border with the superconducting region below ~ 1 K.Comment: 4 pages, 3 figures (published version
Doping dependence of heat transport in the iron-arsenide superconductor Ba(FeCo)As: from isotropic to strongly -dependent gap structure
The temperature and magnetic field dependence of the in-plane thermal
conductivity of the iron-arsenide superconductor
Ba(FeCo)As was measured down to mK and up to
T as a function of Co concentration in the range 0.048 0.114. In zero magnetic field, a negligible residual linear term in
as at all shows that there are no zero-energy
quasiparticles and hence the superconducting gap has no nodes in the -plane
anywhere in the phase diagram. However, the field dependence of
reveals a systematic evolution of the superconducting gap with doping , from
large everywhere on the Fermi surface in the underdoped regime, as evidenced by
a flat at , to strongly -dependent in the overdoped
regime, where a small magnetic field can induce a large residual linear term,
indicative of a deep minimum in the gap magnitude somewhere on the Fermi
surface. This shows that the superconducting gap structure has a strongly
-dependent amplitude around the Fermi surface only outside the
antiferromagnetic/orthorhombic phase.Comment: version accepted for publication in Physical Review Letters; new
title, minor revision, revised fig.1, and updated reference
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