Reversible magnetization measurement of the anisotropy of the London penetration depth in MgB2 single crystals

TL;DR

This study measures the anisotropy of the London penetration depth in MgB2 single crystals using reversible magnetization, revealing temperature-dependent behavior consistent with two-gap superconductivity.

Contribution

It provides the first detailed experimental analysis of the anisotropy of the London penetration depth in MgB2, supporting the two-gap superconductivity model.

Findings

Anisotropy of the London penetration depth is smaller than that of the upper critical field.

The anisotropy of the London penetration depth increases with temperature.

The behavior aligns with two-gap superconductivity theory.

Abstract

We have studied the anisotropy of the London penetration depth, which was obtained from reversible magnetization measurements with the magnetic field both parallel and perpendicular to the c-axis. The anisotropy of the London penetration depth has a smaller magnitude than the anisotropy of the upper critical field and increases with temperature while that of the upper critical field decreases as reported earlier. This behavior is in sharp contrast with the behaviors of superconductors with one superconducting energy gap. The temperature dependence of the anisotropies of the London penetration depth and of the upper critical field can be well explained within the theory of two-gap superconductivity in MgB2.