852 research outputs found
Discovery of Li2(Pd,Pt)3B superconductors
Critical temperature Tc of the Li2(Pd1-xPtx)3B was reported to be 7-8K for
x=0 and 2.2-2.8K for x=1. In this article we present our preliminary results on
behavior of magnetization-temperature curves with starting composition of Pd-B
precursor, y-Li concentration in LiyPd3B and post-annealing of the Pd-end
compound. Results suggest that to maximize Tc ratio Pd:B should be close to
3:1, while y-Li has to be optimum. The lowest Tc for LiyPd3B was 4.4-4.6K,
while post-annealings at 560 deg. C allowed enhancement of Tc up to 8.2-8.4K.
Compositions Li2Z3B with Z=Ni, Ru, Rh, Re, Ag are not superconducting down to
1.8K. Exception is composition with Re showing superconductivity due to Re3B
compound. All samples were prepared by arc melting.Comment: 6 pages, 5 figs. presented at M2S, 200
Crystal Symmetry, Electron-Phonon Coupling, and Superconducting Tendencies in LiPdB and LiPtB
After theoretical determination of the internal structural coordinates in
LiPdB, we calculate and analyze its electronic structure and obtain the
frequencies of the two phonons (40.6 meV for nearly pure Li mode, 13.0
meV for the strongly mixed Pd-Li mode). Pd can be ascribed a
configuration, but strong 4d character remains up to the Fermi level. Small
regions of flat bands occur at -70 meV at both the and X points.
Comparison of the Fermi level density of states to the linear specific heat
coefficient gives a dynamic mass enhancement of = 0.75. Rough Fermi
surface averages of the deformation potentials of individual Pd and Li
displacements are obtained. While is small, ~ 1.15 eV/\AA
is sizable, and a plausible case exists for its superconductivity at 8 K being
driven primarily by coupling to Pd vibrations. The larger d bandwidth in
LiPtB leads to important differences in the bands near the Fermi
surface. The effect on the band structure of spin-orbit coupling plus lack of
inversion is striking, and is much larger in the Pt compound.Comment: 8 pages and 8embedded figures, to be appeared in PR
Hall effect of quasi-hole gas in organic single-crystal transistors
Hall effect is detected in organic field-effect transistors, using
appropriately shaped rubrene (C42H28) single crystals. It turned out that
inverse Hall coefficient, having a positive sign, is close to the amount of
electric-field induced charge upon the hole accumulation. The presence of the
normal Hall effect means that the electromagnetic character of the surface
charge is not of hopping carriers but resembles that of a two-dimensional
hole-gas system
Superconductivity in metal rich Li-Pd-B ternary Boride
8K superconductivity was observed in the metal rich Li-Pd-B ternary system.
Structural, microstructural, electrical and magnetic investigations for various
compositions proved that Li2Pd3B compound, which has a cubic structure composed
of distorted Pd6B octahedrons, is responsible for the superconductivity. This
is the first observation of superconductivity in metal rich ternary borides
containing alkaline metal and Pd as a late transition metal. The compound
prepared by arc melting has high density, is stable in the air and has an upper
critical field, Hc2(0), of 6T.Comment: 4 pages, 5 figur
Effect of Pt doping on the critical temperature and upper critical field in YNi2-xPtxB2C (x=0-0.2)
We investigate the evolution of superconducting properties by doping
non-magnetic impurity in single crystals of YNi2-xPtxB2C (x=0-0.2). With
increasing Pt doping the critical temperature (Tc) monotonically decreases from
15.85K and saturates to a value ~13K for x>0.14. However, unlike conventional
s-wave superconductors, the upper critical field (HC2) along both
crystallographic directions a and c decreases with increasing Pt doping.
Specific heat measurements show that the density of states (N(EF)) at the Fermi
level (EF) and the Debye temperatures (Theta_D) in this series remains constant
within the error bars of our measurement. We explain our results based on the
increase in intraband scattering in the multiband superconductor YNi2B2C.Comment: ps file with figure
Thermo-magnetic history effects in the vortex state of YNi_2B_2C superconductor
The nature of five-quadrant magnetic isotherms for is different from that for
in a single crystal of YNi2B2C, pointing towards an anisotropic behaviour of
the flux line lattice (FLL). For, a well defined peak effect (PE) and second
magnetization peak (SMP) can be observed and the loop is open prior to the PE.
However, for, the loop is closed and one can observe only the PE. We have
investigated the history dependence of magnetization hysteresis data for by
recording minor hysteresis loops. The observed history dependence in across
different anomalous regions are rationalized on the basis of
su-perheating/supercooling of the vortex matter across the first-order-like
phase transition and possible additional effects due to annealing of the
disordered vortex bundles to the underlying equilibrium state.Comment: 4 pages, 4 figure
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