Quantum oscillations and overcritical torque interaction in Sr₂RuO₄

Sr2RuO4 is the only known layered perovskite oxide superconductor without copper; there is strong evidence for an unconventional (`p-wave') pairing mechanism, and it has recently been shown to possess a cylindrical, `quasi-two-dimensional' Fermi surface. Using Sr2RuO4 as a test case for the detection of quantum oscillations with piezoresistive microcantilevers, the piezolever torque magnetometry technique was successfully implemented on a dilution refrigerator. It was possible to reproduce the quantum-oscillatory magnetization data on all three Fermi surface sheets, in a crystal of microgram mass. Moreover, an absolute estimate of the amplitude of the oscillation is provided. We also investigated the phenomenon of torque interaction which distorts the magnetization signal and introduces harmonics and sidebands to the dHvA spectrum. As the torque interaction effect grows in strength, overcriticality is shown to lead to discrete magnetization jumps and to a near-asymptotically damped `sproing' effect