Magnetically-induced local lattice anomalies and low-frequency nematic fluctuations in the Mott insulator La$_2$O$_3$Fe$_2$Se$_2$

TL;DR

This study uses $^{139}$La NQR to reveal lattice anomalies and nematic fluctuations in the Mott insulator La$_2$O$_3$Fe$_2$Se$_2$, showing how magnetic order influences structural distortions and low-frequency electronic fluctuations.

Contribution

It provides new insights into the interplay between magnetic order, lattice structure, and nematic fluctuations in La$_2$O$_3$Fe$_2$Se$_2$ using nuclear quadrupole resonance techniques.

Findings

Identification of two inequivalent La sites in the antiferromagnetic phase.

Temperature dependence of quadrupole coupling linked to magnetic order.

Detection of low-frequency nematic fluctuations in the paramagnetic phase.

Abstract

We report a study of the Mott insulator La$_2$O$_3$Fe$_2$Se$_2$ by means of $^{139}$La nuclear quadrupole resonance (NQR). The NQR spectra evidence a single La site in the paramagnetic phase and two inequivalent La sites, La1 and La2, in the antiferromagnetically-ordered phase (N\'eel temperature $T_{\rm{N}} \simeq 90$ K). These two sites are characterized by different quadrupole couplings, indicative of distinct lattice and/or charge configurations likely segregated in domains. The dependence of the quadrupole coupling for La2 on temperature suggests that the magnetic order parameter drives the structural distortion. The nuclear spin-lattice and transverse relaxation rates, $1/T_1$ and $1/T_2$, evidence fluctuations in the paramagnetic phase with characteristic frequencies well below the Heisenberg exchange frequency, likely associated with nematic fluctuations.