Orientation-dependent electron-phonon coupling in interfacial superconductors LaAlO3/KTaO3

TL;DR

This study reveals that orientation-dependent electron-phonon coupling at LaAlO3/KTaO3 interfaces influences superconductivity, with a quasi-three-dimensional electron gas and varying coupling strengths across different orientations, impacting transition temperatures.

Contribution

It demonstrates that interfacial orientation affects electron-phonon coupling strength and the dimensionality of the electron gas, providing insights into orientation-dependent superconductivity in oxide interfaces.

Findings

Electron-phonon coupling strength varies with interface orientation.

A quasi-three-dimensional electron gas exists at all orientations.

Stronger coupling correlates with higher superconducting transition temperature.

Abstract

The emergent superconductivity at the LaAlO3/KTaO3 interfaces exhibits a mysterious dependence on the KTaO3 crystallographic orientations. Here we show, by soft X-ray angle-resolved photoemission spectroscopy, that the interfacial superconductivity is contributed by mobile electrons with unexpected quasi-three-dimensional character, beyond the "two-dimensional electron gas" scenario in describing oxide interfaces. At differently-oriented interfaces, the quasi-three-dimensional electron gas ubiquitously exists and spatially overlaps with the small q Fuchs-Kliewer surface phonons. Intriguingly, electrons and the Fuchs-Kliewer phonons couple with different strengths depending on the interfacial orientations, and the stronger coupling correlates with the higher superconducting transition temperature. Our results provide a natural explanation for the orientation-dependent superconductivity, and the first evidence that interfacial orientations can affect electron-phonon coupling strength over several nanometers, which may have profound implications for the applications of oxide interfaces in general.