2,100 research outputs found
Probing the phase diagram of CeRu_2Ge_2 by thermopower at high pressure
The temperature dependence of the thermoelectric power, S(T), and the
electrical resistivity of the magnetically ordered CeRu_2Ge_2 (T_N=8.55 K and
T_C=7.40 K) were measured for pressures p < 16 GPa in the temperature range 1.2
K < T < 300 K. Long-range magnetic order is suppressed at a p_c of
approximately 6.4 GPa. Pressure drives S(T) through a sequence of temperature
dependences, ranging from a behaviour characteristic for magnetically ordered
heavy fermion compounds to a typical behaviour of intermediate-valent systems.
At intermediate pressures a large positive maximum develops above 10 K in S(T).
Its origin is attributed to the Kondo effect and its position is assumed to
reflect the Kondo temperature T_K. The pressure dependence of T_K is discussed
in a revised and extended (T,p) phase diagram of CeRu_2Ge_2.Comment: 7 pages, 6 figure
Scaling behavior of temperature-dependent thermopower in CeAu2Si2 under pressure
We report a combined study of in-plane resistivity and thermopower of the
pressure-induced heavy fermion superconductor CeAu2Si2 up to 27.8 GPa. It is
found that thermopower follows a scaling behavior in T/T* almost up to the
magnetic critical pressure pc ~ 22 GPa. By comparing with resistivity results,
we show that the magnitude and characteristic temperature dependence of
thermopower in this pressure range are governed by the Kondo coupling and
crystal-field splitting, respectively. Below pc, the superconducting transition
is preceded by a large negative thermopower minimum, suggesting a close
relationship between the two phenomena. Furthermore, thermopower of a variety
of Ce-based Kondo-lattices with different crystal structures follows the same
scaling relation up to T/T* ~ 2.Comment: 6 pages, 4 figures. Supplementary Material available on reques
From spin-Peierls to superconductivity: (TMTTF)_2PF_6 under high pressure
The nature of the attractive electron-electron interaction, leading to the
formation of Cooper-pairs in unconventional superconductors has still to be
fully understood and is subject to intensive research. Here we show that the
sequence spin-Peierls, antiferromagnetism, superconductivity observed in
(TMTTF)_2PF_6 under pressure makes the (TM)_2X phase diagram universal. We
argue that the suppression of the spin-Peierls transition under pressure, the
close vicinity of antiferromagnetic and superconducting phases at high pressure
as well as the existence of critical antiferromagnetic fluctuations above T_c
strongly support the intriguing possibility that the interchain exchange of
antiferromagnetic fluctuations provides the pairing mechanism required for
bound charge carriers.Comment: 4 pages, revtex, 4 figures (jpeg,eps,png
Strain enhancement of superconductivity in CePd2Si2 under pressure
We report resistivity and calorimetric measurements on two single crystals of
CePd2Si2 pressurized up to 7.4 GPa. A weak uniaxial stress induced in the
pressure cell demonstrates the sensitivity of the physics to anisotropy. Stress
applied along the c-axis extends the whole phase diagram to higher pressures
and enhances the superconducting phase emerging around the magnetic
instability, with a 40% increase of the maximum superconducting temperature,
Tc, and a doubled pressure range. Calorimetric measurements demonstrate the
bulk nature of the superconductivity.Comment: 4 pages, 4 figure
Effect of disorder on the pressure-induced superconducting state of CeAu2Si2
CeAu2Si2 is a newly discovered pressure-induced heavy fermion superconductor
which shows very unusual interplay between superconductivity and magnetism
under pressure. Here we compare the results of high-pressure measurements on
single crystalline CeAu2Si2 samples with different levels of disorder. It is
found that while the magnetic properties are essentially sample independent,
superconductivity is rapidly suppressed when the residual resistivity of the
sample increases. We show that the depression of bulk Tc can be well understood
in terms of pair breaking by nonmagnetic disorder, which strongly suggests an
unconventional pairing state in pressurized CeAu2Si2. Furthermore, increasing
the level of disorder leads to the emergence of another phase transition at T*
within the magnetic phase, which might be in competition with
superconductivity.Comment: 7 pages, 7 figure
Anisotropy, disorder, and superconductivity in CeCu2Si2 under high pressure
Resistivity measurements were carried out up to 8 GPa on single crystal and
polycrystalline samples of CeCu2Si2 from differing sources in the homogeneity
range. The anisotropic response to current direction and small uniaxial
stresses was explored, taking advantage of the quasi-hydrostatic environment of
the Bridgman anvil cell. It was found that both the superconducting transition
temperature Tc and the normal state properties are very sensitive to uniaxial
stress, which leads to a shift of the valence instability pressure Pv and a
small but significant change in Tc for different orientations with respect to
the tetragonal c-axis. Coexistence of superconductivity and residual
resistivity close to the Ioffe-Regel limit around 5 GPa provides a compelling
argument for the existence of a valence-fluctuation mediated pairing
interaction at high pressure in CeCu2Si2.Comment: 12 pages, 7 figure
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