Spontaneous loop-spin current with topological characters in the Hubbard model

TL;DR

This paper discovers a topological Mott insulating state in the Hubbard model on a honeycomb lattice, characterized by spontaneous loop-spin currents and nontrivial topological invariants, existing even at weak interactions.

Contribution

It demonstrates the existence of a topological Mott insulator with spontaneous spin currents in the Hubbard model, a novel phase not previously identified.

Findings

Existence of a topological Mott insulator at small interactions

Presence of spontaneous loop-spin currents

Nontrivial topological invariants in the gapped state

Abstract

We find a state characterized by a spontaneous loop-spin current and a single-particle gap in the Hubbard model within the variational cluster approach. This state exists for arbitrarily small interaction in a half-filled honeycomb lattice. Moreover, from the calculations of the topological invariants for the interacting system, it is shown that this gapped state has nontrivial topological characters; this state is the topological Mott insulating state. This result implies the ubiquity of topological Mott insulating phases.