346 research outputs found
Observation of the parallel-magnetic-field-induced superconductor-insulator transition in thin amorphous InO films
We study the response of a thin superconducting amorphous InO film with
variable oxygen content to a parallel magnetic field. A field-induced
superconductor-insulator transition (SIT) is observed that is very similar to
the one in normal magnetic fields. As the boson-vortex duality, which is the
key-stone of the theory of the field-induced SIT, is obviously absent in the
parallel configuration, we have to draw conclusion about the theory
insufficiency.Comment: 3 pages, 4 figure
Double sign reversal of the vortex Hall effect in YBa2Cu3O7-delta thin films in the strong pinning limit of low magnetic fields
Measurements of the Hall effect and the resistivity in twinned
YBa2Cu3O7-delta thin films in magnetic fields B oriented parallel to the
crystallographic c-axis and to the twin boundaries reveal a double sign
reversal of the Hall coefficient for B below 1 T. In high transport current
densities, or with B tilted off the twin boundaries by 5 degrees, the second
sign reversal vanishes. The power-law scaling of the Hall conductivity to the
longitudinal conductivity in the mixed state is strongly modified in the regime
of the second sign reversal. Our observations are interpreted as strong,
disorder-type dependent vortex pinning and confirm that the Hall conductivity
in high temperature superconductors is not independent of pinning.Comment: 4 pages, 4 figure
Defect-unbinding and the Bose-glass transition in layered superconductors
The low-field Bose-glass transition temperature in heavy-ion irradiated
Bi_2Sr_2CaCu_2O_8+d increases progressively with increasing density of
irradiation-induced columnar defects, but saturates for densities in excess of
1.5 x10^9 cm^-2. The maximum Bose-glass temperature corresponds to that above
which diffusion of two-dimensional pancake vortices between different vortex
lines becomes possible, and above which the ``line-like'' character of vortices
is lost. We develop a description of the Bose-glass line that is in excellent
quantitative agreement with the experimental line obtained for widely different
values of track density and material parameters.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Investigation of correlation of generated nuclearactive particles in the protonantiproton annihilation at momenta 22.4 and 32 GeV / c
Separation of the individual events
corresponding to antiproton-proton annihilation
gives the possibility to carry out the analysis of
multiparticle correlations for generated particles
and to compare them with corresponding data for
inelastic pp and non-annihilation p̃p interactions..
Investigation of correlation of generated nuclearactive particles in the protonantiproton annihilation at momenta 22.4 and 32 GeV / c
Separation of the individual events
corresponding to antiproton-proton annihilation
gives the possibility to carry out the analysis of
multiparticle correlations for generated particles
and to compare them with corresponding data for
inelastic pp and non-annihilation p̃p interactions..
Vortices in coupled planes with columnar disorder and bosonic ladders
We consider two coupled strongly correlated bosonic chains. We derive the
phase diagram of the pure system and obtain an antisymmetric charge density
wave, a 4k_F charge density wave, a superfluid phase and a second superfluid
phase which is a condensate of boson pairs. We consider the effect of a weak
disorder on that system and show that the superfluid phase is less localized
than in the one chain case. On the other hand, the pinning length of the
antisymmetric charge density wave is shorter than in the one chain case. We
discuss the consequences of these results for two coupled vortex planes with
columnar disorder. We show that in the vortex system there is a conventional
pinned solid phase for 0<T<T_m, a pinned solid phase with superkinks for
T_mT_L. We obtain the critical currents by a
modified Larkin-Ovchinnikov argument and prove that there is a strong reduction
of critical current for T=T_m.Comment: 38 pages, RevTeX, 9 encapsulated PostScript figures submitted to
Phys. Rev. B some misprints corrected. One Reference added. Version to appear
in Phys. Rev.
Possible new vortex matter phases in BSCCO
The vortex matter phase diagram of BSCCO crystals is analyzed by
investigating vortex penetration through the surface barrier in the presence of
a transport current. The strength of the effective surface barrier, its
nonlinearity, and asymmetry are used to identify a possible new ordered phase
above the first-order transition. This technique also allows sensitive
determination of the depinning temperature. The solid phase below the
first-order transition is apparently subdivided into two phases by a vertical
line extending from the multicritical point.Comment: 11 pages, 3 figures, accepted for publication in PR
Transport and Magnetic Properties of R1-xAxCoO3 (R=La, Pr and Nd; A=Ba, Sr and Ca)
Transport and magnetic measurements have been carried out on perovskite
Co-oxides R1-xAxCoO3 (R=La, Pr, and Nd; A=Ba, Sr and Ca; 0<x<0.5: All sets of
the R and A species except Nd1-xBaxCoO3 have been studied.). With increasing
the Sr- or Ba-concentration x, the system becomes metallic ferromagnet with
rather large magnetic moments. For R=Pr and Nd and A=Ca, the system approaches
the metal- insulator phase boundary but does not become metallic. The magnetic
moments of the Ca-doped systems measured with the magnetic field H=0.1 T are
much smaller than those of the Ba- and Sr-doped systems. The thermoelectric
powers of the Ba- and Sr-doped systems decrease from large positive values of
lightly doped samples to negative ones with increasing doping level, while
those of Ca-doped systems remain positive. These results can be understood by
considering the relationship between the average ionic radius of R1-xAx and the
energy difference between the low spin and intermediate spin states. We have
found the resistivity-anomaly in the measurements of Pr1-xCaxCoO3 under
pressure in the wide region of x, which indicates the existence of a phase
transition different from the one reported in the very restricted region of
x~0.5 at ambient pressure [Tsubouchi et al. Phys. Rev. B 66 (2002) 052418.]. No
indication of this kind of transition has been observed in other species of R.Comment: 9 pages, 8 figures. J. Phys. Soc. Jpn. 72 (2003) No.
Physical properties of misfit-layered (Bi,Pb)-Sr-Co-O system: Effect of hole doping into triangular lattice formed by low-spin Co ions
Pb-doping effect on physical properties of misfit-layered (Bi,Pb)-Sr-Co-O
system, in which Co ions form a two-dimensional triangular lattice, was
investigated in detail by electronic transport, magnetization and specific-heat
measurements. Pb doping enhances the metallic behavior, suggesting that
carriers are doped. Pb doping also enhances the magnetic correlation in this
system and increases the magnetic transition temperature. We found the
existence of the short-range magnetic correlation far above the transition
temperature, which seems to induce the spin-glass state coexisting with the
ferromagnetic long-range order at low temperatures. Specific-heat measurement
suggests that the effective mass of the carrier in (Bi,Pb)-Sr-Co-O is not
enhanced so much as reported in NaCoO. Based on these experimental
results, we propose a two-bands model which consists of narrow and
rather broad bands. The observed magnetic property and
magnetotransport phenomena are explained well by this model
Hydrodynamics and Nonlocal Conductivities in Vortex States of Type II Superconductors
A hydrodynamical description for vortex states in type II superconductors is
presented based on the time-dependent Ginzburg-Landau equation (TDGL). In
contrast to the familiar extension of a single vortex dynamics based on the
force balance, our description is consistent with the known hydrodynamics of a
rotating neutral superfluid and correctly includes informations on the
Goldstone mode. Further it enables one to examine nonlocal conductivities
perpendicular to the magnetic field in terms of Kubo formula. The nonlocal
conductivities deviate from the usual vortex flow expressions typically when
the nonlocality parallel to the field becomes weaker than the perpendicular one
measuring a degree of positional correlations, and, for instance, the
superconducting contribution of dc Hall conductivity nonlocal only in
directions perpendicular to the field becomes vanishingly small in the
situations with large shear viscosity, leading to an experimentally measurable
relation among the total resistivity components.
Other situations are also discussed on the basis of the resulting expressions.Comment: 12 pages, no figures, to appear in J. Phys. Soc. Jpn. in October,
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