Vibrating sample experiments as a probe of anisotropic torque in YBCO single crystals

Ultrasonic investigations of high-Tc superconductors have been quite successful in determining the magnetic field and temperature dependence of the interaction between magnetic vortices and defect structures in the superconducting state. Recent advances in ultrasonic techniques, allowing the separation of effects due to coupling of the vortex ensemble to modulations of the superconducting current density from those due to pinning, show evidence of reentrant softening of the vortex ensemble as precursor to reentrant melting. It is demonstrated how a related experimental setup can be used to study the magnetic field-induced torque acting on a sample. Torque experiments on highly anisotropic superconductors yield valuable information about the anisotropy of the reduced mass of charge-carriers and the penetration depth. Important advantages of the approach described here over conventional torque experiments are: (a) high sensitivity to small changes in torque even at high ‘bias’-torque; and (b) constant angle between applied magnetic field and sample during the whole experiment, a property that is most important when investigating highly anisotropic superconducting samples in the presence of a magnetic field. Experimental results on a test system show the principle of operation, and investigations of a high-Tc superconducting sample are presented.