A composite electron-lattice order: electronic nematicity of 2DEG and polarization density waves at a near-ferroelectric interface

TL;DR

This paper predicts a novel composite electron-lattice ordered state at ferroelectric interfaces, exhibiting intertwined polarization density waves and electronic nematicity, with implications for understanding anisotropic transport phenomena.

Contribution

It introduces a microscopic theory of a coupled electron-lattice order, explaining nematicity and transport anomalies at ferroelectric interfaces, and highlights the role of collective sliding dynamics under external fields.

Findings

Identification of a polarization density wave coexisting with electronic stripe order.

Explanation of anisotropic quasiparticle spectra and nematicity in 2DEG.

Prediction of enhanced nematic signals due to collective sliding under electric fields.

Abstract

We consider a two-dimensional electron gas (2DEG) formed at a near-ferroelectric interface and strongly coupled to polar phonons. Through a self-consistent microscopic many-body calculation, we show that the coupled system stabilizes a composite electron-lattice ordered state in which the lattice polarization spontaneously forms a polarization density wave (PDW), accompanied by an electronic stripe order in the 2DEG. This intertwined order partially reconstructs the electronic spectrum and generates a twofold quasiparticle anisotropy, giving rise to electronic nematicity at the single-particle level. However, under strong external electric fields, the nematic response becomes dominated by the collective sliding dynamics of the composite order: the sliding motion overwhelms the quasiparticle anisotropy and produces a strongly enhanced nematic signal with higher-order angular harmonics. The theory offers a natural explanation for several anomalous transport and anisotropic responses recently observed at the KTaO$_3$ (111) interface. We also estimate the mean-field transition temperature of this emergent ordered state, obtaining good agreement with experiments, and analyze its evolution with several tuning parameters. The proposed composite order, along with the field-induced crossover from quasiparticle-driven to sliding-dominated nematicity, provides a distinct mechanism of nematicity arising from many-body effects and collective dynamics in critical electron-boson systems, with applicability beyond ferroelectric platforms.