Measurements of record high T_c superconductivity in cuprates under pressure

Probing high temperature superconductivity in systems under extreme pressures presents experimental challenges due to the small sizes and inhomogeneous nature of samples arising from pressure gradients and the presence of mixed phases. As signals in these experiments are small and noise-resolved using many conventional measurement techniques such as AC magnetic susceptibility, new more sensitive probes are needed. To this end we use novel measurement techniques such as radio frequency based probes and SQUID compatible pressure cells to extend the pressure range of magnetic measurements of these cuprates such as near optimally doped Bi₂Sr₂Ca₂Cu₃O_10+δ up to megabar pressures. We calibrate these new techniques based on the established superconducting critical temperature - pressure relations of these materials. The results support the existence of a second superconducting dome of in pressure-overdoped cuprates.