Probing Broken Symmetries of Quantum Materials by Resonant Ultrasound Spectroscopy
Determining the broken symmetries at a thermodynamic phase transition is an essential tool for understanding, or at least constraining, the microscopic mechanisms that lead to novel ground states in quantum materials. Resonant Ultrasound Spectroscopy (RUS) is a characterization technique that measures the spectrum of mechanical resonances of a solid, which allows the determination of its elastic tensor, a thermodynamic quantity that contains symmetry specific information of the ground state. Tracking the evolution of the elastic tensor through a phase transition allows determining which symmetries are broken in the transition, and to propose better suited order parameters.
In this talk I will present RUS measurements of unconventional superconductors and other novel materials, and I will discuss how this tool can reveal the presence of exotic fluctuating order parameters. For example, I will show how our results for the La2-xSrxCuO4 cuprate superconductor reveal the presence of electronic nematic fluctuations across its phase diagram, as evidence in the strong Curie-Weiss softening of the C66 elastic shear moduli. This softening is fully truncated by the opening of the superconducting gap, implying that the origin of such softening is electronic nematic and not elastic as previously thought.