Zernike Colloquium - Paul Chu : A Possible New Paradigm to Higher Temperature Superconductors

Paul C. W. Chu

University of Houston Science Center

Texas Center for Superconductivity

Houston, TX, USA

In the last 28 years, great progress has been made in all areas of high temperature superconductivity (HTS) research following the extensive effort world-wide. Many new compounds have been discovered, the superconducting temperature T_c has been raised from 35 K to 134 at ambient and 164  K at 30 GPa, many models have been proposed to explain the myriad of intriguing anomalous properties and many prototypes devices have been constructed and tested with performance superior to their non-superconducting counterparts. Unfortunately, the T_c has stagnated at 164 K since 1994, a commonly accepted microscopic theory is still elusive and commercialization of HTS is yet-to-be realized. Perhaps, it is time to leave the comfortable but less productive path and dive into the wood occasionally to search for new paths. In this talk, I shall discuss two possible paths: enhanced superconductivity through interfaces and through ultrahigh pressures. I shall present our recent direct evidence for a T_c up to 35 K in undoped CaFe₂As₂ single crystals through low temperature annealing and examine the recent report of 203 K T_c in H_nS under 200 GPa by Eremets et al. with specific emphasis on its magnetic state.