Multiorbital character of the density wave instability in La$_4$Ni$_3$O$_{10}$

TL;DR

This study uses polarized Raman scattering and model calculations to reveal the multiorbital nature and energy scale of density wave instabilities in La$_4$Ni$_3$O$_{10}$, providing insights into their interplay with superconductivity.

Contribution

It demonstrates the multiorbital origin of the density wave gap in La$_4$Ni$_3$O$_{10}$ using combined experimental and theoretical approaches.

Findings

Identification of 114 meV as the density wave gap energy scale.

Observation of phonon anomalies below the transition temperature.

Evidence for non-mean-field behavior of the density wave gap.

Abstract

Ruddlesden-Popper nickelates exhibit high-temperature superconductivity closely intertwined with charge and spin density wave order. However, fundamental questions persist regarding the interplay between the associated density wave (DW) fluctuations and superconductivity, as well as the orbital character and symmetry underlying the DW instabilities. Here we utilize polarized Raman scattering to investigate the phononic and electronic Raman responses of the trilayer nickelate La$_4$Ni$_3$O$_{10}$ across its concomitant charge and spin density wave transitions. In addition to distinct phonon anomalies occurring below the transition temperature, we observe a depletion of continuum spectral weight up to 114 meV and a pronounced peak centered at this energy. By combining momentum-selective information from polarized electronic Raman scattering with model calculations involving both Ni-3$d_{x^2 - y^2}$ and Ni-3$d_{z^2}$ orbitals, we identify 114 meV as the energy scale $2\Delta_\mathrm{DW}$ of the DW gap, characterized by incoherent opening and non-mean-field behavior. Furthermore, the model calculations reveal that the corresponding $2\Delta_\mathrm{DW}$ peak exhibits a multiorbital origin, thus shedding light on the nature of the DW instabilities in La$_4$Ni$_3$O$_{10}$.