125 research outputs found
Hiperplazia benignă de prostată - aspecte actuale de diagnostic şi de tratament (state of the art lecture)
Extreme vortex pinning in the non-centrosymmetric superconductor CePtSi
We report on the vortex dynamics of a single crystal of the
non-centrosymmetric heavy-fermion superconductor CePtSi. Decays of the
remnant magnetization display a clean logarithmic time dependence with rates
that follow the temperature dependence expected from the Kim-Anderson theory.
The creep rates are lower than observed in any other centrosymmetric
superconductor and are not caused by high critical currents. On the contrary,
the critical current in CePtSi is considerably lower than in other
superconductors with strong vortex pinning indicating that an alternative
impediment on the flux line motion might be at work in this superconductor.Comment: 4 pages, 5 figure
Possible re-entrant superconductivity in EuFe2As2 under pressure
We studied the temperature-pressure phase diagram of EuFe2As2 by measurements
of the electrical resistivity. The antiferromagnetic spin-density-wave
transition at T_0 associated with the FeAs-layers is continuously suppressed
with increasing pressure, while the antiferromagnetic ordering temperature of
the Eu 2+ moments seems to be nearly pressure independent up to 2.6 GPa. Above
2 GPa a sharp drop of the resistivity, \rho(T), indicates the onset of
superconductivity at T_c \approx 29.5 K. Surprisingly, on further reducing the
temperature \rho(T) is increasing again and exhibiting a maximum caused by the
ordering of the Eu 2+ moments, a behavior which is reminiscent of re-entrant
superconductivity as it is observed in the ternary Chevrel phases or in the
rare-earth nickel borocarbides
Coupled SDW and Superconducting Order in FFLO State of CeCoIn
The mechanism of incommensurate (IC) spin-density-wave (SDW) order observed
in the Flude-Ferrell-Larkin-Ovchinnikov (FFLO) phase of CeCoIn is discussed
on the basis of new mode-coupling scheme among IC-SDW order, two
superconducting orders of FFLO with B () symmetry
and -pairing of odd-parity. Unlike the mode-coupling schemes proposed by
Kenzelmann et al, Sciencexpress, 21 August (2008), that proposed in the present
Letter can offer a simple explanation for why the IC-SDW order is observed only
in FFLO phase and the IC wave vector is rather robust against the magnetic
field.Comment: 3pages, 1 figure, accepted for publication in J. Phys. Soc. Jpn.,
Vol.77 (2008), No.1
Vortex avalanches in the non-centrosymmetric superconductor Li2Pt3B
We investigated the vortex dynamics in the non-centrosymmetric superconductor
Li_2Pt_3B in the temperature range 0.1 K - 2.8 K. Two different logarithmic
creep regimes in the decay of the remanent magnetization from the Bean critical
state have been observed. In the first regime, the creep rate is
extraordinarily small, indicating the existence of a new, very effective
pinning mechanism. At a certain time a vortex avalanche occurs that increases
the logarithmic creep rate by a factor of about 5 to 10 depending on the
temperature. This may indicate that certain barriers against flux motion are
present and they can be opened under increased pressure exerted by the
vortices. A possible mechanism based on the barrier effect of twin boundaries
is briefly discussed
The role of hyperfine coupling in magnetic and quadrupolar ordering of Pr3Pd20Si6
We study the ternary clathrate Pr3Pd20Si6 in specific heat and
AC-susceptibility measurements on a high-quality single crystal, distinguishing
antiferromagnetic (AFM) and antiferroquadrupolar (AFQ) ordering on two
sublattices of inequivalent Pr sites. The specific heat shows the direct
involvement of nuclear spin degrees of freedom in the AFM ordering, which is
well supported by our calculation of the hyperfine level scheme without
adjustable parameters. Pr3Pd20Si6 is therefore one of the rare materials where
the nuclear moments are involved in the formation of the magnetic ground state.Comment: 5 pages, 5 figure
Fully gapped superconductivity in Ni-pnictide superconductors BaNi2As2 and SrNi2P2
We have performed low-temperature specific heat and thermal conductivity
measurements on the Ni-pnictide superconductors BaNiAs
(=0.7 K and SrNiP (=1.4 K). The temperature
dependences and of the two compounds are similar to the
results of a number of s-wave superconductors. Furthermore, the concave field
responses of the residual for BaNiAs rules out the presence of
nodes on the Fermi surfaces. We postulate that fully gapped superconductivity
could be universal for Ni-pnictide superconductors. Specific heat data on
BaLaNiAs shows a mild suppression of and
relative to BaNiAs.Comment: 5 pages, 3 figures, to be published in J. Phys.: Conf. Se
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