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

Abstract

We examine the superconducting anisotropy $γ_c = (m_c / m_{ab})^{1/2}$ of a metallic high-$T_c$ superconductor MgB$_2$ by measuring the magnetic torque of a single crystal. The anisotropy $γ_c$ does not depend sensitively on the applied magnetic field at 10 K. We obtain the anisotropy parameter $γ_c = 4.31 \pm 0.14$. 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.

REVTeX 4, To be published in Physical Review B