Re-Symmetrizing the Broken Symmetry with Isotropic Hydrostatic Pressure

TL;DR

This paper reports a discovery that isotropic hydrostatic pressure can induce degeneracy between Landau levels in quantum systems, revealing sensitive pseudospin polarization transitions in correlated quantum liquids.

Contribution

It demonstrates a novel method to fine-tune Landau level degeneracy using hydrostatic pressure, advancing control over quantum phases in condensed matter systems.

Findings

Hydrostatic pressure induces degeneracy between two lowest Landau levels.

Pseudospin polarization transitions are observed near Landau level filling factor 3/2.

Pressure tuning affects quantum liquid phase transitions with high sensitivity.

Abstract

Recent progresses in condensed matter physics, such as graphene, topological insulator and Weyl semimetal, often origin from the specific topological symmetries of their lattice structures. Quantum states with different degrees of freedom, e.g. spin, valley, layer, etc., arise from these symmetries, and the coherent superpositions of these states form multiple energy subbands. The pseudospin, a concept analogy to the Dirac spinor matrices, is a successful description of such multi-subband systems. When the electron-electron interaction dominates, many-body quantum phases arise. They usually have digitized pseudospin polarizations and exhibit sharp phase transitions at certain universal critical pseudospin energy splittings. In this manuscript, we present our remarkable discovery of hydrostatic pressure induced degeneracy between the two lowest Landau levels. This degeneracy is evidenced by the pseudospin polarization transitions of the fragile correlated quantum liquid phases near Landau level filling factor $\nu$ = 3/2. Benefitted from the constant hole concentration and the sensitive nature of these transitions, we can study the fine-tuning effect of the hydrostatic pressure of the order of 10 $\mu$eV, well beyond the meV-level state-of-the-art resolution of other techniques.