Superconducting anisotropy and evidence for intrinsic pinning in single crystalline MgB$_2$

TL;DR

This study measures the anisotropy of MgB₂ using magnetic torque, revealing intrinsic pinning effects and providing evidence for superconductivity within boron layers, with an anisotropy ratio of approximately 4.3.

Contribution

It presents the first detailed measurement of superconducting anisotropy in MgB₂ and provides experimental evidence for intrinsic pinning related to boron layers.

Findings

Anisotropy parameter γ_c ≈ 4.3 at 10 K.

Intrinsic pinning observed via sharp hysteresis peak.

Superconductivity occurs in boron layers.

Abstract

We examine the superconducting anisotropy $\gamma_c = (m_c / m_{ab})^{1/2}$ of a metallic high-$T_c$ superconductor MgB$_2$ by measuring the magnetic torque of a single crystal. The anisotropy $\gamma_c$ does not depend sensitively on the applied magnetic field at 10 K. We obtain the anisotropy parameter $\gamma_c = 4.31 \pm 0.14$. The torque curve shows the sharp hysteresis peak when the field is applied parallel to the boron layers. This comes from the intrinsic pinning and is experimental evidence for the occurrence of superconductivity in the boron layers.