Optical control of the crystal structure in the bilayer nickelate superconductor La3Ni2O7 via nonlinear phononics

TL;DR

This study proposes using nonlinear phononics and light irradiation to control the crystal structure of La3Ni2O7, potentially influencing its superconducting properties without applying pressure.

Contribution

It introduces a theoretical method to manipulate the crystal structure of La3Ni2O7 via optical excitation of lattice vibrations, avoiding the need for high pressure.

Findings

Light-induced IR phonon excitation slightly straightens the Ni-O-Ni bond angle.

Nonlinear Raman-mode displacement can be achieved through anharmonic phonon coupling.

The approach offers a new way to control crystal structure optically.

Abstract

Superconductivity in the bilayer nickelate La$_3$Ni$_2$O$_7$ occurs when the interlayer Ni-O-Ni bond angle becomes straight under pressure, suggesting a strong relationship between the crystal structure and the emergence of superconductivity. In this study, we theoretically propose a way to control the crystal structure of La$_3$Ni$_2$O$_7$ toward the tetragonal symmetry via light irradiation instead of pressure using the idea of nonlinear phononics. Here, resonant optical excitation of an infrared-active (IR) lattice vibration induces a nonlinear Raman-mode displacement through the anharmonic phonon-phonon coupling. We calculate the light-induced phonon dynamics on the anharmonic lattice potential determined by first-principles calculation. We find that the interlayer Ni-O-Ni bond angle gets slightly closer to straight when an appropriate IR mode is selectively excited. Our study suggests that light irradiation can be a promising way for structural control of La$_3$Ni$_2$O$_7$.