Theory for the hysteretic properties of the low-field dc magnetization in type-II superconductors

Magnetic Studies of Superconductivity in the Ga-Sn Alloy Regular Nanostructures

For applications of nanolattices in low-temperature nanoelectronics, the inter-unit space can be filled with superconducting metallic alloys. However, superconductivity under nanoconfinement is expected to be strongly affected by size-effects and other factors. We studied the magnetic properties and structure of the Ga-Sn eutectic alloy within regular nanopores of an opal template, to understand the specifics of the alloy superconductivity. Two superconducting transitions were observed, in contrast to the bulk alloy. The transitions were ascribed to the segregates with the structures of tetragonal tin and a particular gallium polymorph. The superconducting-phase diagram was constructed, which demonstrated crossovers from the positive- to the common negative-curvature of the upper critical-field lines. Hysteresis was found between the susceptibilities obtained at cooling and warming in the applied magnetic field.

Routes to probe Bismuth induced strong-coupling superconductivity in bimetallic BiIn alloys

We report the observation of strong electron-phonon coupling in intergranular linked BiIn superconductors over an infinite range mediated by low-lying phonons. An enhanced superconducting transition temperature was observed from the magnetization, revealing a main diamagnetic Meissner state below T_C(0) = 5.86(1) K and a critical field H_C(0) = 1355(15) Oe with an In₂Bi phase of the composite sample. The electron-phonon coupling to low lying phonons is found to be the leading mechanism for observed strong-coupling superconductivity in the BiIn system. Our findings suggest that In₂Bi is in the strong-coupling region with T_C(0) = 5.62(1) K, λ_ep = 1.45, ω_ln = 45.92 K and α = 2.23. The estimated upper critical field can be well-described by a power law with α value higher than 2, consistent with the strong electron-phonon coupling.

Paramagnetic magnetization signals and curious metastable behaviour in field-cooled magnetization of a single crystal of superconductor 2H-NbSe2

We present here some newer characteristics pertaining to paramagnetic Meissner effect like response in a single crystal of the low [Formula: see text] superconducting compound 2H-[Formula: see text] via a detailed study of effects of perturbation on the field-cooled magnetization response. In the temperature range, where an anomalous paramagnetic magnetization occurs, the field-cooled magnetization response is found to be highly metastable: it displays a curious tendency to switch randomly from a given paramagnetic value to a diamagnetic or to a different paramagnetic value, when the system is perturbed by an impulse of an externally applied ac magnetic field. The new facets revealed in a single crystal of 2H-[Formula: see text] surprisingly bear a marked resemblance with the characteristics of magnetization behaviour anticipated for the giant vortex states with multiple flux quanta ([Formula: see text], [Formula: see text], [Formula: see text]) predicted to occur in mesoscopic-sized superconducting specimen and possible transitions amongst such states.