264 research outputs found
Fermi Surface of KFeAs from Quantum Oscillations in Magnetostriction
We present a study of the Fermi surface of KFeAs single crystals.
Quantum oscillations were observed in magnetostriction measured down to 50 mK
and in magnetic fields up to 14 T. For , the calculated
effective masses are in agreement with recent de Haas-van Alphen and ARPES
experiments, showing enhanced values with respect to the ones obtained from
previous band calculations. For , we observed a small orbit at a
cyclotron frequency of 64 T, characterized by an effective mass of , supporting the presence of a three-dimensional pocket at the Z-point.Comment: SCES Conference, Tokyo 201
Signatures of pressure induced superconductivity in insulating Bi2212
We have performed several high pressure electrical resistance experiments on
Bi1.98Sr2.06Y0.68Cu2O8, an insulating parent compound of the high-Tc Bi2212
family of copper oxide superconductors. We find a resistive anomaly, a downturn
at low temperature, that onsets with applied pressure in the 20-40 kbar range.
Through both resistance and magnetoresistance measurements, we identify this
anomaly as a signature of induced superconductivity. Resistance to higher
pressures decreases Tc, giving a maximum of 10 K. The higher pressure
measurements exhibit a strong sensitivity to the hydrostaticity of the pressure
environment. We make comparisons to the pressure induced superconductivity now
ubiquitous in the iron arsenides.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
High-pressure study of non-Fermi liquid and spin-glass-like behavior in CeRhSn
We present measurements of the temperature dependence of electrical
resistivity of CeRhSn up to ~ 27 kbar. At low temperatures, the electrical
resistivity varies linearly with temperature for all pressures, indicating
non-Fermi liquid behavior. Below a temperature Tf ~ 6 K, the electrical
resistivity deviates from a linear dependence. We found that the
low-temperature feature centered at T = Tf shows a pressure dependence dTf/dP ~
30 mK/kbar which is typical of canonical spin glasses. This interplay between
spin-glass-like and non-Fermi liquid behavior was observed in both CeRhSn and a
Ce0.9La0.1RhSn alloy.Comment: 5 pages, 3 figures, accepted for publication to Journal of Physics:
Condensed Matte
Bose-Einstein Condensation of S = 1 Ni spin degrees of freedom in NiCl2-4SC(NH2)2
It has recently been suggested that the organic compound
NiCl-4SC(NH) (DTN) exhibits Bose-Einstein Condensation (BEC) of the
Ni spin degrees of freedom for fields applied along the tetragonal c-axis. The
Ni spins exhibit 3D XY-type antiferromagnetic order above a field-induced
quantum critical point at T. The Ni spin fluid can be
characterized as a system of effective bosons with a hard-core repulsive
interaction in which the antiferromagnetic state corresponds to a Bose-Einstein
condensate (BEC) of the phase coherent Ni spin system. We have
investigated the the high-field phase diagram and the occurrence of BEC in DTN
by means of specific heat and magnetocaloric effect measurements to dilution
refrigerator temperatures. Our results indicate that a key prediction of BEC is
satisfied; the magnetic field-temperature quantum phase transition line
approaches a power-law at low temperatures,
with an exponent at the quantum critical point,
consistent with the BEC theory prediction of .Comment: 4 pages, 4 figure
High pressure transport studies of the LiFeAs analogues CuFeTe2 and Fe2As
We have synthesized two iron-pnictide/chalcogenide materials, CuFeTe2 and
Fe2As, which share crystallographic features with known iron-based
superconductors, and carried out high-pressure electrical resistivity
measurements on these materials to pressures in excess of 30 GPa. Both
compounds crystallize in the Cu2Sb-type crystal structure that is
characteristic of LiFeAs (with CuFeTe2 exhibiting a disordered variant). At
ambient pressure, CuFeTe2 is a semiconductor and has been suggested to exhibit
a spin-density-wave transition, while Fe2As is a metallic antiferromagnet. The
electrical resistivity of CuFeTe2, measured at 4 K, decreases by almost two
orders of magnitude between ambient pressure and 2.4 GPa. At 34 GPa, the
electrical resistivity decreases upon cooling the sample below 150 K,
suggesting the proximity of the compound to a metal-insulator transition.
Neither CuFeTe2 nor Fe2As superconduct above 1.1 K throughout the measured
pressure range.Comment: 6 pages, 7 figure
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