1,823 research outputs found
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
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
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
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 pressure cycling on Iron: Signatures of an electronic instability and unconventional superconductivity
High pressure electrical resistivity and x-ray diffraction experiments have
been performed on Fe single crystals. The crystallographic investigation
provides direct evidence that in the martensitic
transition at 14 GPa the become the directions. During a pressure cycle, resistivity shows a
broad hysteresis of 6.5 GPa, whereas superconductivity, observed between 13 and
31 GPa, remains unaffected. Upon increasing pressure an electronic instability,
probably a quantum critical point, is observed at around 19 GPa and, close to
this pressure, the superconducting and the isothermal resistivity
(K) attain maximum values. In the superconducting pressure domain,
the exponent of the temperature power law of resistivity and its
prefactor, which mimics , indicate that ferromagnetic fluctuations may
provide the glue for the Cooper pairs, yielding unconventional
superconductivity
Probing the extended non-Fermi liquid regimes of MnSi and Fe
Recent studies show that the non-Fermi liquid (NFL) behavior of MnSi and Fe
spans over an unexpectedly broad pressure range, between the critical pressure
p_c and around 2p_c. In order to determine the extension of their NFL regions,
we analyze the evolution of the resistivity rho(T) A(p)T^n at higher pressures.
We find that in MnSi the n=3/2 exponent holds below 4.8 GPa=3 p_c, but it
increases above that pressure. At 7.2 GPa we observe the low temperature Fermi
liquid exponent n=2 whereas for T>1.5 K, n=5/3. Our measurements in Fe show
that the NFL behavior rho T^{5/3} extends at least up to 30.5 GPa, above the
entire superconducting (SC) region. In the studied pressure range, the onset of
the SC transition reduces by a factor 10 down to T_c^onset(30.5 GPa)=0.23 K,
while the A-coefficient diminishes monotonically by around 50%.Comment: 2 pages, 2 figures, Proceedings SCES 200
Hidden Variables in Bipartite Networks
We introduce and study random bipartite networks with hidden variables. Nodes
in these networks are characterized by hidden variables which control the
appearance of links between node pairs. We derive analytic expressions for the
degree distribution, degree correlations, the distribution of the number of
common neighbors, and the bipartite clustering coefficient in these networks.
We also establish the relationship between degrees of nodes in original
bipartite networks and in their unipartite projections. We further demonstrate
how hidden variable formalism can be applied to analyze topological properties
of networks in certain bipartite network models, and verify our analytical
results in numerical simulations
Heavy Fermion superconductor CeCuSi under high pressure: multiprobing the valence crossover
The first heavy fermion superconductor CeCuSi has not revealed all
its striking mysteries yet. At high pressures, superconductivity is supposed to
be mediated by valence fluctuations, in contrast to ambient pressure, where
spin fluctuations most likely act as pairing glue. We have carried out a
multiprobe (electric transport, thermopower, ac specific heat, Hall and Nernst
effects) experiment up to on a high quality CeCuSi
single crystal. Reliable resistivity data reveal for the first time a scaling
behavior close to the supposed valence transition, and allow to locate the
critical end point at and a slightly negative
temperature. In the same pressure region, remarkable features have also been
detected in the other physical properties, acting as further signatures of the
Ce valence crossover and the associated critical fluctuations.Comment: 13 pages, 14 figure
High-pressure transport properties of CeRu_2Ge_2
The pressure-induced changes in the temperature-dependent thermopower S(T)
and electrical resistivity \rho(T) of CeRu_2Ge_2 are described within the
single-site Anderson model. The Ce-ions are treated as impurities and the
coherent scattering on different Ce-sites is neglected. Changing the
hybridisation \Gamma between the 4f-states and the conduction band accounts for
the pressure effect. The transport coefficients are calculated in the
non-crossing approximation above the phase boundary line. The theoretical S(T)
and \rho(T) curves show many features of the experimental data. The seemingly
complicated temperature dependence of S(T) and \rho(T), and their evolution as
a function of pressure, is related to the crossovers between various fixed
points of the model.Comment: 9 pages, 10 figure
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