Electronic layer decoupling driven by density-wave order in La$_4$Ni$_3$O$_{10}$

TL;DR

This study investigates the density-wave transition in La$_4$Ni$_3$O$_{10}$ using polarization-resolved infrared spectroscopy, revealing anisotropic electronic behavior and layer decoupling driven by spin-density-wave order.

Contribution

It demonstrates that a spin-density-wave induces electronic decoupling in La$_4$Ni$_3$O$_{10}$, evidenced by anisotropic electrodynamics and phonon shifts, highlighting a new mechanism in layered nickelates.

Findings

Out-of-plane conductivity sharply suppressed in the ordered phase

Anisotropic electrodynamics with metallic in-plane and insulating out-of-plane behavior

Phonon shifts indicating density-wave instability

Abstract

We probe the density-wave transition of the trilayer nickelate La$_4$Ni$_3$O$_{10}$ with polarization-resolved infrared spectroscopy. The low-energy electrodynamics is strongly anisotropic, with metallic in-plane and insulating out-of-plane character. In the ordered phase, the anisotropy grows more than an order of magnitude as the out-of-plane conductivity is sharply suppressed. We interpret this enhancement as an effective electronic decoupling of the Ni-O layers, driven by a spin-density-wave-induced redistribution of Ni-$d_{z^2}$ occupation within the trilayers. This electronic response is accompanied by clear shifts and splittings of the out-of-plane phonons, compatible with a density-wave instability of electronic origin.