664 research outputs found
Wiedemann-Franz law and non-vanishing temperature scale across the field-tuned quantum critical point of YbRh2Si2
The in-plane thermal conductivity kappa(T) and electrical resistivity rho(T)
of the heavy-fermion metal YbRh2Si2 were measured down to 50 mK for magnetic
fields H parallel and perpendicular to the tetragonal c axis, through the
field-tuned quantum critical point, Hc, at which antiferromagnetic order ends.
The thermal and electrical resistivities, w(T) and rho(T), show a linear
temperature dependence below 1 K, typical of the non-Fermi liquid behavior
found near antiferromagnetic quantum critical points, but this dependence does
not persist down to T = 0. Below a characteristic temperature T* ~ 0.35 K,
which depends weakly on H, w(T) and rho(T) both deviate downward and converge
in the T = 0 limit. We propose that T* marks the onset of short-range magnetic
correlations, persisting beyond Hc. By comparing samples of different purity,
we conclude that the Wiedemann-Franz law holds in YbRh2Si2, even at Hc,
implying that no fundamental breakdown of quasiparticle behavior occurs in this
material. The overall phenomenology of heat and charge transport in YbRh2Si2 is
similar to that observed in the heavy-fermion metal CeCoIn5, near its own
field-tuned quantum critical point.Comment: 8 figures, 8 page
Heat Transport in a Strongly Overdoped Cuprate: Fermi Liquid and Pure d-wave BCS Superconductor
The transport of heat and charge in the overdoped cuprate superconductor
Tl_2Ba_2CuO_(6+delta) was measured down to low temperature. In the normal
state, obtained by applying a magnetic field greater than the upper critical
field, the Wiedemann-Franz law is verified to hold perfectly. In the
superconducting state, a large residual linear term is observed in the thermal
conductivity, in quantitative agreement with BCS theory for a d-wave
superconductor. This is compelling evidence that the electrons in overdoped
cuprates form a Fermi liquid, with no indication of spin-charge separation.Comment: 4 pages, 2 figures, published version, title changed, Phys. Rev.
Lett. 89, 147003 (2002
Doping dependence of superconducting gap in YBa_2Cu_3O_y from universal heat transport
Thermal transport in the T -> 0 limit was measured as a function of doping in
high-quality single crystals of the cuprate superconductor YBa_2Cu_3O_y. The
residual linear term kappa_0/T is found to decrease as one moves from the
overdoped regime towards the Mott insulator region of the phase diagram. The
doping dependence of the low-energy quasiparticle gap extracted from kappa_0/T
is seen to scale closely with that of the pseudogap, arguing against a
non-superconducting origin for the pseudogap. The presence of a linear term for
all dopings is evidence against the existence of a quantum phase transition to
an order parameter with a complex (ix) component.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding
Ballistic magnon transport and phonon scattering in the antiferromagnet NdCuO
The thermal conductivity of the antiferromagnet NdCuO was measured
down to 50 mK. Using the spin-flop transition to switch on and off the acoustic
Nd magnons, we can reliably separate the magnon and phonon contributions to
heat transport. We find that magnons travel ballistically below 0.5 K, with a
thermal conductivity growing as , from which we extract their velocity. We
show that the rate of scattering of acoustic magnons by phonons grows as ,
and the scattering of phonons by magnons peaks at twice the average Nd magnon
frequency.Comment: 4 pages, 3 figures, one figure modifie
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.
Low-temperature phonon thermal conductivity of cuprate single crystals
The effect of sample size and surface roughness on the phonon thermal
conductivity of NdCuO single crystals was studied down to 50
mK. At 0.5 K, is proportional to , where is the
cross-sectional area of the sample. This demonstrates that is
dominated by boundary scattering below 0.5 K or so. However, the expected
dependence of is not observed down to 50 mK. Upon roughing the
surfaces, the dependence is restored, showing that departures from
are due to specular reflection of phonons off the mirror-like sample surfaces.
We propose an empirical power law fit, to (where
) in cuprate single crystals. Using this method, we show that
recent thermal conductivity studies of Zn doping in YBaCuO
re-affirm the universal heat conductivity of d-wave quasiparticles at .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
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