Creation of hyperoxia superconducting phase in La2CuO4 by applying shear strain under high-pressure compression

Abstract

We successfully stabilized the hyperoxia superconducting phase of La2CuO4, the parent insulating compound of La-based cuprate superconductors, by applying compression under high pressure and successive shear strains via the process of high-pressure torsion (HPT). Superconducting phases in the La2CuO4 system are created via the hole doping by replacing the La-sites with alkali-earth metals or by overdoping oxygen. However, the present study demonstrates that the HPT processing induces structural strain, and subsequent annealing stabilizes the hyperoxia phase, i.e., the superoxide phase. The superconducting transition temperature Tc systematically varies as a function of the revolution number N in HPT processing under compression of 6 GPa, and Tc has the maximum value of approximately 40 K for N≤1. Stabilized superconducting states intrinsically have a large critical field at the 20 T level. This approach proposes a high-pressure material synthesis method that is useful for mechanically tuning carriers in insulating La2CuO4.