High-temperature superconductivity

About: High-temperature superconductivity is a research topic. Over the lifetime, 7263 publications have been published within this topic receiving 175377 citations. The topic is also known as: high-temperature superconductivity.

Novel technique to measure the microwave response of high Tc superconductors between 4.2 and 200 K

Abstract: This paper describes a novel technique for measurements of the complex surface impedance Z(s) of high-T(c) superconductors over an extremely wide range of temperature, from 4.2 K and at least 200 K. The technique uses a superconducting Pb-plated Cu high-Q-cavity resonator operated at an ambient temperature of 4.2 K, with the sample (typically a 3-mm-diam x 1-mm-thick disk) mounted on a sapphire rod in the center of cavity, at a high B-field and thermally insulated from the cavity walls, making it possible to control the sample temperature externally. Since the cavity characteristics are dominated by the sample properties (the contribution of the Pb-covered walls maintained at 4.2 K is negligible), measurement of the cavity Q and resonant frequency makes it possible to measure Zs as a function of the sample temperature. The Z(s) values for bulk Y1Ba2Cu3O(y) and La(1.85)Sr(0.15)CuO4 were measured over a temperature range 4.2-100 K.

Photoinduced enhancement of superconductivity

Abstract: We show clear and conclusive experimental evidence for the enhancement of superconductivity in GdBa2Cu3Ox and YBa2Cu3Ox thin films by photoexcitation. Upon laser illumination the critical temperature increases while the resistivity of the material decreases. The relaxation back to the original state is very slow, of the order of days at room temperature. The existence of this effect opens the possibility of fabricating weak‐link devices with in situ tunable superconducting characteristics.

Long-range Coulomb interactions and the onset of superconductivity in the high-Tc materials.

Abstract: The Ginzburg-Landau functional for a superconductor is extended to include a quantum-fluctuation term arising from imperfect screening of the long-range Coulomb interaction. At low temperatures the resulting quantum {ital x}-{ital y} model shows a second-order phase transition between a superconducting state and an insulating state as a function of the ratio of the phase stiffness to the Coulomb energy measured on the scale of the mean pair spacing. By relating the functional formulation to a BCS-type model of high-temperature superconductivity in the strongly correlated regime, we show that the phase stiffness is proportional to doping away from the 1/2-full Mott insulating state. We discuss application of the model as a mechanism for the onset of superconductivity of the CuO{sub 2}-based high-{ital T}{sub {ital c}} materials above a critical doping level. Transport and optical properties of materials with reduced transition temperature are calculated.

Absence of current direction dependence of the resistive state of high temperature superconductors in magnetic fields

Abstract: Resistive transition of Bi 2 Sr 2 CaCu 2 O 8+ y film in magnetic fields is studied in the light of the currently proposed flux creep model. Measurements with precise angular alignment have clarified that the resistive transition does not depend on the relative direction between magnetic field and transport current. This calls for a significant revision of the Lorentz-force-driven flux creep picture. A fluctuation induced phase-slip phenomenon as an alternative model is also discussed.

Oxygen Isotope Effect and Structural Phase Transitions in La2CuO4-Based Superconductors.

Abstract: The oxygen isotope effect on the superconducting transition temperature (α o ) varies as a function of x in La 2-x Sr x CuO 4 and La 2-x Ba x CuO 4 , with the maximum α o values (α o ≥ 0.5) found for x near 0.12. This unusual x dependence implies that the isotope effect is influenced by proximity to the Abma → P4 2 /ncm structural phase transition in these systems. Synchrotron x-ray difaction measurements reveal little change in lattice parameters or orthorhombicity due to isotope exchange in strontium-doped materials where α o > 0.5, eliminating static structural distortion as a cause of the large isotope effects. The anomalous behavior of α o in both strontium- and barium-doped materials, in combination with the previously discovered Abma → P4 2 /ncm structural phase-transition in La 1.88 B 0.12 CuO 4 , suggests that an electronic contribution to the lattice instability is present and maximizes at ∼1/8 hole per copper atom. These observations indicate a dose connection between hole doping of the Cu-O sheets, tilting instabilities of the CuO 6 octahedra, and superconductivity in La 2 CuO 4 -based superconductors.