Hardening of Ni-O bond-stretching phonons in LaNiO$_2$

TL;DR

This study uses advanced theoretical methods to show that electron correlations and magnetic fluctuations significantly influence phonon behavior in LaNiO$_2$, impacting its lattice dynamics and electronic properties relevant to superconductivity.

Contribution

It demonstrates the importance of dynamical electron correlation and magnetic fluctuations in phonon spectra of LaNiO$_2$, revealing their effects on bond-stretching phonons and charge order absence.

Findings

Optical Ni-O bond-stretching phonons harden with increased electron correlation.

Strong local electron correlation does not favor charge order coupling to phonons.

Magnetic fluctuations influence lattice dynamics and may explain ARPES kink features.

Abstract

We demonstrate that dynamical electron correlation and fluctuating local magnetic moments are crucial for the phonon spectra of the infinite-layer nickelate superconductor, LaNiO$_2$, using DFT plus dynamical mean-field theory (DFT+DMFT) calculations. We find significant hardening of optical Ni-O bond-stretching phonons when going from non-magnetic to paramagnetic state, and increasing Coulomb interaction will make them even harder. The electron correlation is found to be sensitive to the Ni-O bond-stretching distortions, indicating strong interplay between electron correlation and lattice. We find that the strong local electron correlation will not favor charge orders that couple to the Ni-O bond-stretching phonons, in support of the recent experiment that a $3a_0$ charge order is absent in the infinite-layer nickelates. Our results emphasize that the effects of local magnetic fluctuations should be fully taken into account when describing the lattice dynamics of the infinite-layer nickelates without long-range magnetic orders, and also provide evidence to ascribe the kink observed in the recent angle-resolved photoemission experiment to possible strong electron coupling to the Ni-O bond-stretching phonons.