Basal-Plane Magnetic Anisotropies of High-kappa d-Wave Superconductors in a Mixed State: A Quasiclassical Approach

Abstract

We study the basal-plane anisotropies of reversible magnetization and torque in a mixed state of layered d-wave superconductors based on the quasiclassical version of the BCS-Gor'kov theory. Both the longitudinal magnetization (\(M_L\)) and torque (\(\tau\)) show fourfold oscillations as a function of the field angle \(\chi\). The relationship between the node position and the oscillatory patterns shown by \(M_L\) and \(\tau\) is clarified. It is also shown that the sign of the \(\tau (\chi)\)-oscillation does not change between \(H_{c1}\) and \(H_{c2}\), while the sign of the \(M_L (\chi)\)-oscillation changes. The newly obtained result for \(\tau\) indicates that the torque experiment can allow us to detect the in-plane anisotropies of \(H_{c2}\) even in a material with strong fluctuations such as cuprate or organic superconductors, where the \(H_{c2}\) itself cannot be determined experimentally.