Uncovering the role of shear in nickelate superconductivity using nanoscale quantum sensing

Nickelate materials play a crucial role in the decades-long quest to probe, understand and enhance high-temperature superconductivity. They provide a fresh perspective on the unconventional physics of the cuprates, realizing similar electronic and structural motifs in a wholly different material platform. Recently, a tremendous amount of excitement has focused on the discovery of superconductivity in the bulk nickelate, La3Ni2O7, at high pressures, with a critical temperature above the boiling point of liquid nitrogen. However, in addition to the presence of substantial variations in the superconducting properties measured across different samples, many measurements of La3Ni2O7 have also observed strikingly low superconducting volume fractions, leading the superconductivity to be dubbed "filamentary"; such observations complicate our understanding of both the nature of nickelate superconductivity, as well as the underlying connection to the cuprates. In this talk, I will describe a crucial step toward addressing these challenges enabled by the NV-DAC – a new high-pressure sensing platform in which Nitrogen-Vacancy color centers are directly implanted within the culet of the diamond anvil cell. With sub-micron spatial resolution, I will describe the results of directly correlating local regions of nickelate superconductivity with spatial maps of both the stress environment and the chemical composition. In particular, by decomposing pressure into its uniaxial and shear stress components, we will arrive at a refined three-dimensional, superconducting phase diagram.