Electronic Nematicity Revealed by Polarized Ultrafast Spectroscopy in Bilayer La$_3$Ni$_2$O$_7$

TL;DR

This study uses polarized ultrafast spectroscopy to reveal electronic nematicity in bilayer La$_3$Ni$_2$O$_7$, showing anisotropic dynamics that may be linked to its superconducting properties, unlike the isotropic trilayer La$_4$Ni$_3$O$_{10}$.

Contribution

It demonstrates the presence of electronic nematicity in bilayer La$_3$Ni$_2$O$_7$ through ultrafast spectroscopy, highlighting a potential connection to superconductivity.

Findings

La$_3$Ni$_2$O$_7$ exhibits $C_2$ electronic anisotropy at low temperatures.

La$_4$Ni$_3$O$_{10}$ remains isotropic across temperatures.

Electronic nematicity may be related to superconducting pairing in La$_3$Ni$_2$O$_7$.

Abstract

We report a polarized ultrafast pump-probe study of the normal-state electronic dynamics in bilayer La$_3$Ni$_2$O$_7$ and trilayer La$_4$Ni$_3$O$_{10}$ single crystals at ambient pressure. While both nickelates exhibit density-wave (DW) transitions accompanied by the opening of a quasiparticle relaxation bottleneck, their electronic responses display strikingly different symmetry properties. La$_4$Ni$_3$O$_{10}$ maintains an isotropic optical response across the entire temperature range. In contrast, La$_3$Ni$_2$O$_7$ exhibits a pronounced twofold ($C_2$) anisotropy in its low-temperature electronic dynamics. This electronic nematicity, evident in both the relaxation dynamics and the effective gap scales, competes with a secondary isotropic order emerging below 115 K. The presence of macroscopic electronic anisotropy in the bilayer system, and its absence in the trilayer system, suggests an intimate relation between electronic nematic fluctuations and superconducting pairing in La$_3$Ni$_2$O$_7$ that worth for deeper explorations.