Absence of phonon-mediated superconductivity in La$_3$Ni$_2$O$_7$ under pressure

TL;DR

This study investigates the phonon properties and electron phonon coupling in La$_3$Ni$_2$O$_7$ under high pressure, concluding that phonons alone cannot explain its high-temperature superconductivity, suggesting an unconventional pairing mechanism.

Contribution

The paper provides the first detailed phonon and electron phonon interaction analysis for La$_3$Ni$_2$O$_7$ under pressure, challenging phonon-mediated superconductivity as the sole mechanism.

Findings

Electron phonon coupling is too weak to account for high $T_c$.

Strong Fermi surface nesting may cause charge density wave transition.

La$_3$Ni$_2$O$_7$ is likely an unconventional superconductor.

Abstract

A recent experimental study announced the emergence of superconductivity in La$_3$Ni$_2$O$_7$ under pressure, with the highest observed superconducting transition temperature ($T_c$) reaching approximately 80 K beyond 14 GPa. While extensive studies have been devoted to the electronic correlations and potential superconducting pairing mechanisms, there lack investigations into the phonon properties and electron phonon coupling. Using density functional theory in conjunction with Wannier interpolation techniques, we study the phonon properties and electron phonon interactions in La$_3$Ni$_2$O$_7$ under 29.5 GPa. Our findings reveal that the electron phonon coupling is insufficient to solely explain the observed high superconducting $T_c$ $\sim$ 80 K in La$_3$Ni$_2$O$_7$. And the calculated strong Fermi surface nesting may explain the experimental observed charge density wave transition in La$_3$Ni$_2$O$_7$. Our calculations substantiate La$_3$Ni$_2$O$_7$ is an unconventional superconductor.