Origin of superconductivity transition broadening in MgB2

TL;DR

This study investigates the broadening of the superconducting transition in MgB2, attributing it to superconducting fluctuations or vortex-liquid behavior rather than surface effects, influenced by MgB2's short coherence length and high transition temperature.

Contribution

It provides experimental evidence linking transition broadening in MgB2 to vortex-liquid states, emphasizing the role of anisotropic magnetic field effects and superconducting fluctuations.

Findings

Transition broadening is independent of Lorentz force.

Broadening depends on magnetic field direction.

Superconducting fluctuation or vortex-liquid state is responsible.

Abstract

We report resistivity and magnetization of single crystal MgB2, focusing on the broadening of superconducting (SC) transition in magnetic fields. In-plane and out-of-plane resistivity indicate that the broadening of superconducting transition is independent of Lorentz force and that it is merely dependent on the magnetic field direction. In magnetization, diamagnetic signal begins to appear at almost the same temperature as the onset temperature of resistivity transition. These results suggest that the broadening is attributed not to the surface superconductivity but to the superconducting fluctuation or the vortex-liquid picture, owing to the short coherence length and the high transition temperature of MgB2.