High Pressure Studies of Cuprate High Temperature Superconductors

Since the discovery of high temperature superconductivity in La5−xBaxCu5O5(3−y) at an unprecedented 35 K over 35 years ago the nature superconductivity in cuprates has been intensely studied, with the use of pressure as an experimental parameter often playing a critical role. The effect of pressure on cuprate superconductivity is analogous to the effect of hole doping, with experiments establishing a pressure- Tc relation that closely tracks the well established hole doping concentration (nH)- Tc relation in nearly all cuprates. The structure and electronic properties of cuprate superconductors with nominal composition Bi2Sr2Can−1CunO2n+4+δ (n=1,2,3) have been studied using x-ray diffraction and magnetic susceptibility up to 144 GPa for n=3, 100 GPa for n=2, and 50 GPa for n=1. Anomalous compression mechanisms were observed in all three compounds, which allowed us to reconcile discrepancies in the literature. The development of novel techniques to characterize these materials is discussed, with an emphasis on complications that arise in high pressure environments. Finally, connections to the non-monotonic behavior of Tc in pressurized Bi1.6Pb0.4Sr2Ca2Cu3O10+δ are discussed, with data suggesting a second superconducting dome for pressure overdoped cuprates that are typically not stable at ambient conditions. This second superconducting dome supports significantly higher Tc’s than the well known ambient pressure dome.