269 research outputs found
Low-Temperature Rapid Synthesis and Superconductivity of Fe-Based Oxypnictide Superconductors
we were able to develop a novel method to synthesize Fe-based oxypnictide
superconductors. By using LnAs and FeO as the starting materials and a
ball-milling process prior to solid-state sintering, Tc as high as 50.7 K was
obtained with the sample of Sm 0.85Nd0.15FeAsO0.85F0.15 prepared by sintering
at temperatures as low as 1173 K for times as short as 20 min.Comment: 2 pages,2 figures, 1 tabl
Fluctuation and Order of Antiferromagnetism induced by Paramagnetic Pair-Breaking in Superconducting Vortex Lattice
Effects of the strong Pauli-paramagnetic pair-breaking (PPB) on the vortex
lattice in d-wave superconductors are theoretically studied by putting emphasis
on consequences of the PPB-induced antiferromagnetic (AFM) ordering in the
spatial modulation in the vortex lattice. It is shown that the PPB-induced AFM
fluctuation in the superconducting state leads to an enhancement of the vortex
lattice form factor which is a measure of spatial variations of the internal
magnetic field and that the enhancement becomes more remarkable as an AFM
instability is approached. It is also demonstrated that the PPB-induced AFM
ordering is assisted by the vortex-lattice modulation, and thus, that the
resulting AFM order is spatially modulated, while it is not localized in the
vortex cores but coexistent with the nonvanishing superconducting order
parameter. These results are discussed in connection with two phenomena
observed in CeCoIn5, the anomalous field dependence of the vortex lattice form
factor and the AFM order appearing inside the high-field and low-temperature
superconducting phase.Comment: 26 pages, 13 figure
Superconducting Properties of MgB2 Bulk Materials Prepared by High Pressure Sintering
High-density bulk materials of a newly discovered 40K intermetallic MgB2
superconductor were prepared by high pressure sintering. Superconducting
transition with the onset temperature of 39K was confirmed by both magnetic and
resistive measurements. Magnetization versus field (M-H) curve shows the
behavior of a typical Type II superconductor and the lower critical field
Hc1(0) estimated from M-H curve is 0.032T. The bulk sample shows good
connection between grains and critical current density Jc estimated from the
magnetization hysteresis using sample size was 2x104A/cm2 at 20K and 1T. Upper
critical field Hc2(0) determined by extrapolating the onset of resistive
transition and assuming a dirty limit is 18T.Comment: 3Pages PD
Temperature dependence of the superheating field for superconductors in the high-k London limit
We study the metastability of the superheated Meissner state in type II
superconductors with k >> 1 beyond Ginzburg-Landau theory, which is applicable
only in the vicinity of the critical temperature. Within Eilenberger's
semiclassical approximation, we use the local electrodynamic response of the
superconductor to derive a generalized thermodynamic potential valid at any
temperature. The stability analysis of this functional yields the temperature
dependence of the superheating field. Finally, we comment on the implications
of our results for superconducting cavities in particle accelerators.Comment: 7.5 pages, 2 figure
Enhancement of Superconductivity in Disordered Films by Parallel Magnetic Field
We show that the superconducting transition temperature T_c(H) of a very thin
highly disordered film with strong spin-orbital scattering can be increased by
parallel magnetic field H. This effect is due to polarization of magnetic
impurity spins which reduces the full exchange scattering rate of electrons;
the largest effect is predicted for spin-1/2 impurities. Moreover, for some
range of magnetic impurity concentrations the phenomenon of {\it
superconductivity induced by magnetic field} is predicted: superconducting
transition temperature T_c(H) is found to be nonzero in the range of magnetic
fields .Comment: 4 pages, 2 figure
Hall Coefficient of Equilibrium Supercurrents Flowing inside Superconductors
We study augmented quasiclassical equations of superconductivity with the
Lorentz force, which is missing from the standard Ginzburg-Landau and
Eilenberger equations. It is shown that the magnetic Lorentz force on
equilibrium supercurrents induces finite charge distribution and the resulting
electric field to balance the Lorentz force. An analytic expression is obtained
for the corresponding Hall coefficient of clean type-II superconductors with
simultaneously incorporating the Fermi-surface and gap anisotropies. It has the
same sign and magnitude at zero temperature as the normal state for an
arbitrary pairing, having no temperature dependence specifically for the s-wave
pairing. The gap anisotropy may bring a considerable temperature dependence in
the Hall coefficient and can lead to its sign change as a function of
temperature, as exemplified for a model d-wave pairing with a two-dimensional
Fermi surface. The sign change may be observed in some high-
superconductors.Comment: 7 pages, 3 figure
The BCS critical temperature in a weak external electric field via a linear two-body operator
We study the critical temperature of a superconductive material in a weak
external electric potential via a linear approximation of the BCS functional.
We reproduce a similar result as in [Frank, Hainzl, Seiringer, Solovej, 2016]
using the strategy introduced in [Frank, Hainzl, Langmann, 2018], where we
considered the case of an external constant magnetic field.Comment: Dedicated to Herbert Spohn on the occasion of his seventieth
birthday; 29 page
The BCS Critical Temperature in a Weak External Electric Field via a Linear Two-Body Operator
We study the critical temperature of a superconductive material in a weak external electric potential via a linear approximation of the BCS functional. We reproduce a similar result as in Frank et al. (Commun Math Phys 342(1):189–216, 2016, [5]) using the strategy introduced in Frank et al. (The BCS critical temperature in a weak homogeneous magnetic field, [2]), where we considered the case of an external constant magnetic field
Superconducting Properties under Magnetic Field in NaCoOHO Single Crystal
We report the in-plane resistivity and magnetic susceptibility of the layered
cobalt oxide NaCoOHO single crystal. The
temperature dependence of the resistivity shows metallic behavior from room
temperature to the superconducting transition temperature of 4.5 K.
Sharp resistive transition, zero resistivity and almost perfect superconducting
volume fraction below indicate the good quality and the bulk
superconductivity of the single crystal. The upper critical field and
the coherence length are obtained from the resistive transitions in
magnetic field parallel to the c-axis and the -plane. The anisotropy of
, 12 nm/1.3 nm 9.2, suggests that this
material is considered to be an anisotropic three dimensional superconductor.
In the field parallel to the -plane, seems to be suppressed to the
value of Pauli paramagnetic limit. It may indicate the spin singlet
superconductivity in the cobalt oxide.Comment: 4 pages, 4 figure
Superconductivity Induced by Bond Breaking in the Triangular Lattice of IrTe2
IrTe2, a layered compound with a triangular iridium lattice, exhibits a
structural phase transition at approximately 250 K. This transition is
characterized by the formation of Ir-Ir bonds along the b-axis. We found that
the breaking of Ir-Ir bonds that occurs in Ir1-xPtxTe2 results in the
appearance of a structural critical point in the T = 0 limit at xc = 0.035.
Although both IrTe2 and PtTe2 are paramagnetic metals, superconductivity at Tc
= 3.1 K is induced by the bond breaking in a narrow range of x > xc in
Ir1-xPtxTe2. This result indicates that structural fluctuations can be involved
in the emergence of superconductivity.Comment: 10 pages, 4 figure
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