Tunable superconductivity and spin density wave in La3Ni2O7/LaAlO3 thin films

TL;DR

This study combines first-principles calculations and renormalization group analysis to explore how interlayer distance influences superconductivity and magnetic order in La3Ni2O7/LaAlO3 thin films, revealing tunable phases.

Contribution

It provides a systematic theoretical investigation of the relationship between interlayer distance and emergent phases in La3Ni2O7 thin films, explaining experimental observations and predicting pressure effects.

Findings

Superconductivity emerges with dominant pairing between Ni 3d_{3z^2-r^2} orbitals.

Smaller interlayer distance favors G-type spin density wave; larger favors C-type.

Applied pressure reduces superconducting transition temperature, inducing a spin density wave.

Abstract

Recently, La3Ni2O7 thin film on the LaAlO3 substrate is shown to be superconducting, while the bulk La3Ni2O7 with the same in-plane lattice constant under pressure does not superconduct. This difference suggests the interlayer distance $d_{\rm Ni-Ni}$ is crucial to control superconductivity, and its variation under pressure may tune the ground state sensitively. We investigate systematically the La3Ni2O7/LaAlO3 thin films in a reasonable range of $d_{\rm Ni-Ni}$, by a combination of the first-principle calculations and the singular-mode functional renormalization group. For smaller (larger) $d_{\rm Ni-Ni}$, the ground state is a C-type (G-type) spin density wave with spins coupled ferromagnetically (antiferromagnetically) across the two layers. Between the two phases, $s_\pm$-wave superconductivity emerges with dominant pairings between nickel $3d_{3z^2-r^2}$ orbitals. The results explain the experimental superconductivity in the thin film under ambient pressure, and predict that the applied pressure will decrease the superconducting transition temperature, until the system enters the C-type spin density wave. Experimental verification would provide profound insights into the nature of electron correlations in this system, since the C-type spin density wave is achieved most naturally in the itinerant picture, while it would be hard in the local moment picture where spins are always coupled antiferromagnetically across the layers.