Compatible Instability: Gauge Constraints of Elasticity Inherited by Electronic Nematic Criticality

TL;DR

This paper develops a formalism for electronic nematicity in quantum materials that respects elastic compatibility, revealing how constraints bifurcate nematic fluctuations into critical and gapped sectors, leading to universal direction-selective criticality.

Contribution

It introduces a gauge-invariant nemato-elasticity formalism that enforces compatibility constraints, explaining nematic criticality and domain phenomena in crystalline materials.

Findings

Compatibility constraints bifurcate nematic fluctuations into critical and gapped sectors.

Critical nematic modes are protected from defect-induced pinning effects.

Universal direction-selective nematic criticality emerges in crystals.

Abstract

Electronic nematicity is widely observed in quantum materials with varying degrees of electronic correlation, manifesting through charge, spin, orbital, or superconducting degrees of freedom. A phenomenological model capable of describing this broad set of systems must also account for nemato-elasticity, by which nematic and elastic degrees of freedom become intertwined. However, being a tensor gauge field theory, elasticity must satisfy the compatibility relations which guarantee the integrability of lattice deformations. Here, we develop a formalism for nemato-elasticity that manifestly respects the elastic compatibility relations. We show that these constraints bifurcate the phase space of nematic fluctuations into two orthogonal sectors: one compatible and thus critical, the other incompatible and therefore gapped. The suppression of the latter leads to universal direction-selective nematic criticality in any crystal lattice. Moreover, the critical nematic modes are protected from pinning effects induced by microscopic defect strains, which necessarily induce both longitudinal and transverse correlated random fields. Finally, our results also reconcile seemingly contradictory nematic phenomena, such as the mean-field character of the nematic transition and the widespread presence of domain formation.