Manifestation Of Superconductivity Research Articles

On the criteria for superconducting superlattices using CaCuO2 *

The manifestation of superconductivity in cuprate superconductors is concerted to copper-oxygen planes. To maintain charge neutrality, the copper-oxygen planes are embedded between materials, that are electronically insulating. Here, we introduce BaBiO3, LaCrO3, EuFeO3, and Ca2Fe2O5 as candidate materials. We use molecular beam epitaxy as a synthesis tool for the development of artificial superconducting superlattices in combination with infinte-layer CaCuO2. We find that (1) layer lattice matching, (2) thermodynamic compatibility and (3) absence of diffusion of any element other than Cu into CuO2 planes are key criteria to realize superconductivity. For brown-millerite Ca2Fe2O5/CaCuO2 superlattices, criteria 1–3 are met and superconductivity emerges.

Superconductivity in FeTe1−xSx Induced by Electrochemical Reaction Using Ionic Liquid Solution

Superconductivity in FeTe0.8S0.2 is successfully induced by an electrochemical reaction using an ionic liquid solution. A clear correlation between the Fe concentration in the solution and the manifestation of superconductivity was confirmed, suggesting that superconductivity was induced by the deintercalation of excess iron.

Realization and characterization of solid-solid (BEDT-TTF)/iodine C-T composites exhibiting metallic conductivity down to 0.34 K.

It is shown that the organic composite obtained by a direct solid-solid C-T reaction between BEDT-TTF and iodine is metallic from 300 to 0.34 K. There is also a clear manifestation of superconductivity below 5 K, which is confirmed by the particular dependence of the electrical resistivity on magnetic field, up to 30 kG.

Polysomatic Series and Superconductivity in Complex Cuprates with Ladder-Type Structure

The structure of ladder-type cuprates was considered in polysomatic model. The possibility of the manifestation of superconductivity was estimated considering the structural stability of various cuprates with the ladder-type structure.

SUPERCONDUCTIVITY IN 2+1 DIMENSIONS VIA KOSTERLITZ-THOULESS MECHANISM: LARGE N AND FINITE TEMPERATURE ANALYSES

We analyze a (2+1)-dimensional model with charged, relativistic fermions interacting through a four-fermi term. Taking advantage of its large N renormalizability, the various phases of this model are studied at finite temperature and beyond the leading order in 1/N. Although the vacuum expectation value (VEV) of a charged order parameter is zero at any nonzero temperature, the model nevertheless exhibits a rich phase structure in the strong coupling regime, because of the nonvanishing VEV of a neutral order parameter and due to the nontrivial dynamics of the vortex excitations on the plane. These include a confined vortex phase which is superconducting at low temperatures, an intermediate temperature phase with deconfined vortices, and a high temperature phase, where the neutral order parameter vanishes. The manifestation of superconductivity at low temperatures and its disappearance above a critical temperature is explicitly shown to be due to the vortex confinement/deconfinement mechanism of Kosterlitz and Thouless. The ground state does not break parity or time reversal symmetries and the ratio of the energy gap to Tc is bigger than the conventional BCS value, for N≲22.

Is the tetragonal overdoped phase (La, Sr)2CuO4 superconductive?

Comparative studies of Meissner and shielding processes have been performed on variously sized samples of the solid solution (La1−xSrx)2CuO4: (polycrystalline, powder, and single-crystalline) under various magnetic fields in the range 0.03–10 Oe. Considering the kinetics of the two processes, this systematic approach has indicated that the observed Meissner signal can be significantly low with the sample still being wholly superconductive. Based on this comparative study, the tetragonal region of (La1−xSrx)2CuO4 withx greater than 0.105 has been concluded to be superconductive, suggesting the nonessential involvement of the buckling of the Cu-O-Cu-O bond in the CuO2 layer in the manifestation of superconductivity.

Transition from metallic to tunneling-type conductance in metal-metal and normal-metal-superconductor point contacts.

We have investigated the microshort--to--tunneling crossover in normal-normal ([ital N]-[ital N]) and normal-metal--superconductor ([ital N]-[ital S]) point-contact junctions at 4.2 K as the junction conductance ([ital G][sub 0]) is varied. The microshort (or metallic'') point contact with the dynamic conductance [ital G] ([ital V]) having a negative derivative with respect to bias [ital V] (i.e., [partial derivative][ital G]/[partial derivative][ital V][lt]0) changes over to a tunneling-type junction with [partial derivative][ital G]/[partial derivative][ital V][gt]0 when [ital G][sub 0][congruent]3--5 mS. We show that this is the region where the contact radius [alpha] is a few times [ital k][sub [ital F]][sup [minus]1] ([ital k][sub [ital F]] is the Fermi wave vector) and the crossover in the sign of [partial derivative][ital G]/[partial derivative][ital V] occurs due to electron confinement in a length scale comparable to [ital k][sub [ital F]][sup [minus]1]. The effect of confinement is to make the electrons crossing the constriction evanescent in nature as the junction size is reduced progressively and the energy for lateral confinement becomes comparable to [ital E][sub [ital F]]. We argue that in this extreme ballistic regime, the classical Sharvin approach breaks down as quantum effects due to electron confinement takes over. This happens much before single-atom'' contact ismore » reached which signals the onset of vacuum tunneling. As a further test of the electron confinement effects in point contacts, we investigated clean [ital N]-[ital S] microshorts showing near-ideal Andreev reflection. We find that in [ital N]-[ital S] junctions, the Andreev reflection (which is a manifestation of superconductivity) gradually vanishes when the contact radius [alpha][congruent]0.1[xi] ([xi] is the coherence length) and the energy cost of electron confinement is larger than the superconducting energy gap [Delta].« less

Oxygen nonstoichiometry of the (Nd, Ce)2CuO4−δ system

Abstract Oxygen nonstoichiometry of the electron-doped superconductor Nd1.85Ce0.15CuO4−δ and nondoped Nd2CuO4−δ was determined using thermogravimetry and chemical titration analysis. The oxygen deficiency of Nd2CuO4−δ at 900°C and PO2=10-3 atm was approximately 0.04, while that of Nd1.85Ce0.15CuO4−δ was about 0.008, both being substantially smaller than that of Ba2YCu3O7−δ. In this system, however, a small amount of oxygen defect seems to play an essential role in the manifestations of superconductivity.