Modulation of the Octahedral Structure and Potential Superconductivity of La$_3$Ni$_2$O$_7$ through Strain Engineering

TL;DR

This study uses first-principles calculations to explore how strain and pressure influence the electronic structure and potential superconductivity of La$_3$Ni$_2$O$_7$, revealing pathways to induce superconductivity with minimal compression.

Contribution

It demonstrates that applying about 2 GPa of uniaxial stress along the c axis can induce superconductivity by modulating the Ni-$d_{z^2}$ electron density at the Fermi level.

Findings

Pressure affects Ni-$d_{z^2}$ electron density correlating with superconducting dome shape.

Uniaxial stress of ~2 GPa can potentially induce superconductivity.

Stress influences lattice, band structure, and Fermi surface, guiding experimental efforts.

Abstract

The recent transport measurement of La$_3$Ni$_2$O$_7$ uncover a "right-triangle" shape of the superconducting dome in the pressure-temperature (P-T) phase diagram. Motivated by this, we perform theoretical first-principles studies of La$_3$Ni$_2$O$_7$ with the pressure ranging from 0 to 100 GPa. Notably, we reveal a pressure dependence of the Ni-$d_{z^2}$ electron density at the Fermi energy ($n_z^{EF}$) that highly coincides with such shape. On this basis, we further explore the electronic structure under uniaxial stress. By tracking the stress response of $n_z^{EF}$, we propose that superconductivity can be achieved by applying only about 2 GPa of compression along the c axis. The idea is further exemplified from the perspectives of lattice distortion, band structure, Fermi surface and superconducting phase coherence. We also discuss the possible charge modulation under the stress and provide an insight to the relation between n_z^EF and the superconducting Tc in La$_3$Ni$_2$O$_7$ system. Our study provides a helpful guide to the future experiment.