Theory of Electron Pairing Mediated by Ferroelastic Distortions

The pairing mechanism in LaAlO₃/SrTiO₃ heterointerfaces has remained elusive despite a concentrated experimental and theoretical efforts. Examining the critical current through a series of nanostructures, it was found that the critical current was largely independent of the width of the nanostructure but could be increased by increasing the number of nanowires [Y.-Y. Pai arXiv:1707.01488]. In these nanostructures, a carrier density dependent uplift of the surface has also been observed at room temperature [F. Bi, J. App. Phys. 119, 025309 (2016).], suggesting that the electron doping seeds Z-oriented tetragonal domains while the epitaxial strain favors X/Y-oriented tetragonal domains. From these observations, we propose that electron pairing may be induced at domain walls between these ferrodistortive domains and present the results of a minimal model which couples the structural degrees of freedom to the electron gas.