Tunneling-Induced Restoration of the Degeneracy and the Time-Reversal Symmetry Breaking in Optical Lattices

TL;DR

This paper investigates how tunneling influences degeneracy and time-reversal symmetry breaking in the ground state of bosons in a one-dimensional optical lattice, revealing a phase transition driven by lattice anharmonicity.

Contribution

It demonstrates that tunneling can restore degeneracy and induce spontaneous time-reversal symmetry breaking in the system's ground state, highlighting the role of lattice anharmonicity.

Findings

Degeneracy occurs at specific tunneling strengths.

Time-reversal symmetry is spontaneously broken.

Staggered angular momentum emerges as the ground state.

Abstract

We study the ground-state properties of bosons loaded into the $p$-band of a one dimensional optical lattice. We show that the phase diagram of the system is substantially affected by the anharmonicity of the lattice potential. In particular, for a certain range of tunneling strength, the full many-body ground state of the system becomes degenerate. In this region, an additional symmetry of the system, namely the parity of the occupation number of the chosen orbital, is spontaneously broken. The state with nonvanishing staggered angular momentum, which breaks the time-reversal symmetry, becomes the true ground state of the system.