Why Haven't We Had the YBCO Discovery Yet in the Nickelates?

Abstract

Interest in low valence layered nickelates has greatly increased the past year after the discovery of superconductivity in a doped version of the infinite-layer material, RNiO2, by Harold Hwang’s group.  So far, superconductivity has only been observed in Pr and Nd variants, and only in thin film form.  And to date, the closest material to these in regards to nickel valence is the reduced trilayer materials, R4Ni3O8, where instead stripe formation is seen.  In this talk, I will contrast these 112 and 438 materials, both from an experimental and a theoretical perspective, along with prospects for superconducting 438, and mention the possibility of higher-order reduced Ruddlesden-Popper phases (see Physics 13, 85).