The origin of strain-induced stabilisation of superconductivity in the lanthanum cuprates
Abstract
Suppression of superconductivity in favour of a striped phase, and its coincidence with a structural transition from a low-temperature orthorhombic (LTO) to a low-temperature tetragonal (LTT) phase, is a ubiquitous feature of hole-doped lanthanum cuprates. We study the effect of anisotropic strain on this transition using density-functional theory on both La2CuO4 and the recently-synthesised surrogate La2MgO4 to decouple electronic and structural effects. Strikingly, we find that compressive strain applied diagonally to the in-plane metal-oxygen bonds dramatically stabilises the LTO phase. Given the mutual exclusivity of 3D superconductivity and long-range static stripe order, we thereby suggest a structural mechanism for understanding experimentally-observed trends in the superconducting Tc under uniaxial pressure, and suggest principles for tuning it.