Hidden-symmetry-protected quantum pseudo-spin Hall effect in optical lattices

TL;DR

This paper introduces a new type of Z_2 topological insulator in optical lattices, protected by hidden symmetry rather than time-reversal symmetry, featuring helical edge states and pseudo-spin-momentum locking.

Contribution

It proposes a scheme to realize a novel quantum pseudo-spin Hall effect in optical lattices based on hidden symmetry, expanding topological insulator concepts.

Findings

Identification of hidden symmetry responsible for Z_2 topological order

Characterization of helical edge states with pseudo-spin-momentum locking

Discussion of experimental detection methods

Abstract

We propose a scheme to realize a new Z_2 topological insulator in a square optical lattice. Different from the conventional topological insulator protected by the time-reversal symmetry, here, the optical lattice possesses a novel hidden symmetry, which is responsible for the present Z_2 topological order. With a properly defined pseudo-spin, such a topological insulator is characterized by the helical edge states which exhibits pseudo-spin-momentum locking, so that it can be considered as a quantum pseudo-spin Hall insulator. The Z_2 topological invariant is derived and its experimental detection is discussed as well.