Jahn-Teller distortion on strained La$_3$Ni$_2$O$_7$ thin films

TL;DR

This study investigates how biaxial strain affects the electronic structure and Jahn-Teller distortion in La$_3$Ni$_2$O$_7$ thin films, highlighting strain as a key factor in tuning superconductivity.

Contribution

It reveals that strain enhances Jahn-Teller splitting and influences electronic properties, providing insights into optimizing superconductivity in bilayer nickelates.

Findings

Strain elongates outer apical Ni-O bonds, increasing Jahn-Teller splitting.

Calculated Fermi surfaces match ARPES measurements for different substrates.

Jahn-Teller distortion is identified as a crucial parameter for superconductivity tuning.

Abstract

We present a systematic study of the electronic structure of strained La$_3$Ni$_2$O$_7$ thin films. We show that biaxial compressive strain mainly elongates the outer apical Ni-O bond while leaving the inner apical Ni-O bond nearly unchanged. As a result, the Jahn-Teller splitting $\Delta_{JT}$ is strongly enhanced, whereas the interlayer $d_{z^2}$ hopping $t_\perp^z$ changes only weakly. Since superconductivity is widely believed to emerge only below a critical in-plane lattice constant, our results identify the strain-enhanced $\Delta_{JT}$ as the relevant microscopic tuning parameter. Consistently, the calculated Fermi surfaces and Hall response for LaAlO$_3$ and SrLaAlO$_4$ substrates agree with ARPES and Hall measurements. Our results identify Jahn-Teller distortion as a key tuning parameter in strained La$_3$Ni$_2$O$_7$ and support its central role in optimizing superconductivity in bilayer nickelates.