16 research outputs found
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
Field-induced thermal metal-to-insulator transition in underdoped LSCO
The transport of heat and charge in cuprates was measured in undoped and
heavily-underdoped single crystal La_{2-x}Sr_xCuO_{4+delta} (LSCO). In
underdoped LSCO, the thermal conductivity is found to decrease with increasing
magnetic field in the T --> 0 limit, in striking contrast to the increase
observed in all superconductors, including cuprates at higher doping. The
suppression of superconductivity with magnetic field shows that a novel thermal
metal-to-insulator transition occurs upon going from the superconducting state
to the field-induced normal state.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding
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
Transport in Ultraclean YBaCuO: neither Unitary nor Born Impurity Scattering
The thermal conductivity of ultraclean YBaCuO was measured at
very low temperature in magnetic fields up to 13 T. The temperature and field
dependence of the electronic heat conductivity show that two widespread
assumptions of transport theory applied to unconventional superconductors fail
for clean cuprates: impurity scattering cannot be treated in the usual unitary
limit (nor indeed in the Born limit), and scattering of quasiparticles off
vortices cannot be neglected. Our study also sheds light on the long-standing
puzzle of a sudden onset of a "plateau" in the thermal conductivity of Bi-2212
versus field.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Josephson effect in a weak link between borocarbides
A stationary Josephson effect is analyzed theoretically for a weak link
between borocarbide superconductors. It is shown that different models of the
order parameter result in qualitatively different current-phase relations
Field-induced quantum critical point in CeCoIn_5
The resistivity of CeCoIn_5 was measured down to 20 mK in magnetic fields of
up to 16 T. 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 ~4/3. This is evidence
for a new field-induced quantum critical point, occuring in this case at a
critical field which coincides with the superconducting upper critical field
H_c2.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding
Heat Conduction in the Vortex State of NbSe_2: Evidence for Multi-Band Superconductivity
The thermal conductivity kappa of the layered s-wave superconductor NbSe_2
was measured down to T_c/100 throughout the vortex state. With increasing
field, we identify two regimes: one with localized states at fields very near
H_c1 and one with highly delocalized quasiparticle excitations at higher
fields. The two associated length scales are naturally explained as multi-band
superconductivity, with distinct small and large superconducting gaps on
different sheets of the Fermi surface. This behavior is compared to that of the
multi-band superconductor MgB_2 and the conventional superconductor V_3Si.Comment: 5 pages, 4 figure
Field-Induced Thermal Metal-to-Insulator Transition in Underdoped LSCO
The transport of heat and charge in cuprates was measured in single crystals
of La_{2-x}Sr_xCuO_{4+\delta} (LSCO) across the doping phase diagram at low
temperatures. In underdoped LSCO, the thermal conductivity is found to decrease
with increasing magnetic field in the T goes to 0 limit, in striking contrast
to the increase observed in all superconductors, including cuprates at higher
doping. In heavily underdoped LSCO, where superconductivity can be entirely
suppressed with an applied field, we show that a novel thermal
metal-to-insulator transition takes place upon going from the superconducting
state to the field-induced normal state.Comment: 4 pages, 3 figures, minor changes, replaced with published versio
Doping dependence of the superconducting gap in Tl_2Ba_2CuO_{6+delta} from heat transport
We present low-temperature thermal conductivity measurements on the cuprate
Tl_2Ba_2CuO_{6+delta} throughout the overdoped regime. In the T -> 0 limit, the
thermal conductivity due to d-wave nodal quasiparticles provides a bulk
measurement of the superconducting gap, Delta. We find Delta to decrease with
increasing doping, with a magnitude consistent with spectroscopic measurements
(photoemission and tunneling). This argues for a pure and simple d-wave
superconducting state in the overdoped region of the phase diagram, which
appears to extend into the underdoped regime down to a hole concentration of
0.1 hole/Cu. As hole concentration is decreased, the gap-to-Tc ratio increases,
showing that the suppression of the superconducting transition temperature Tc
(relative to the gap) begins in the overdoped regime.Comment: 7 pages, 4 figure