Breakdown of Landau Fermi liquid theory: restrictions on the degrees of freedom of quantum electrons

TL;DR

This paper proposes that many forms of unconventional electronic physics arise from restrictions on quantum electron degrees of freedom in Landau Fermi liquids, linked to symmetry and topology changes.

Contribution

It introduces a perspective that connects the breakdown of Landau Fermi-liquid theory to symmetry breaking, emergent symmetries, and topology, guiding future research and device design.

Findings

Identifies mechanisms restricting electron degrees of freedom

Classifies unconventional physics beyond traditional Fermi liquids

Provides pathways for studying Fermi liquid breakdown

Abstract

One challenge in contemporary condensed matter physics is to understand unconventional electronic physics beyond the paradigm of Landau Fermi-liquid theory. Here, we present a perspective that posits that most such examples of unconventional electronic physics stem from restrictions on the degrees of freedom of quantum electrons in Landau Fermi liquids. Since the degrees of freedom are deeply connected to the system's symmetries and topology, these restrictions can thus be realized by external constraints or by interaction-driven processes via the following mechanisms: (i) symmetry breaking, (ii) new emergent symmetries, and (iii) nontrivial topology. Various examples of unconventional electronic physics beyond the reach of traditional Landau Fermi liquid theory are extensively investigated from this point of view. Our perspective yields basic pathways to study the breakdown of Landau Fermi liquids and also provides a guiding principle in the search for novel electronic systems and devices.