The origin of strain-induced stabilisation of superconductivity in the lanthanum cuprates

TL;DR

This study uses density-functional theory to show that diagonal compressive strain stabilizes the orthorhombic phase in lanthanum cuprates, providing insights into how strain influences superconductivity and stripe order.

Contribution

It demonstrates that anisotropic strain can control structural phases in lanthanum cuprates, revealing a structural mechanism affecting superconductivity.

Findings

Diagonal compressive strain stabilizes the LTO phase.

Strain influences the competition between superconductivity and stripe order.

Structural tuning can potentially optimize superconducting properties.

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 La$_2$CuO$_4$ and the recently-synthesised surrogate La$_2$MgO$_4$ 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 $T_{\mathrm{c}}$ under uniaxial pressure, and suggest principles for tuning it.