Symmetric topological Mott insulator and Mott semimetal

TL;DR

This paper introduces symmetric topological Mott insulators and semimetals in moiré materials, revealing new phases with quantized Hall responses and edge modes, driven by exciton pairing and sublattice potential tuning.

Contribution

It proposes the existence of symmetric topological Mott insulators beyond Slater determinants, with explicit models and phase transitions, including a Mott semimetal at criticality.

Findings

Existence of symmetric topological Mott insulators with quantized Hall responses.

Identification of a Mott semimetal at the phase transition point.

Proposal of a ferromagnetic Chern insulator in MoTe2/WSe2 heterostructures.

Abstract

Correlated physics in nearly flat topological bands is a central theme in the study of moir\'e materials. While ground states at integer fillings are typically identified as quantum Hall ferromagnets within a Hartree-Fock framework, we propose the existence of symmetric topological Mott insulators (STMIs) that transcend this Slater determinant picture. Focusing on half-filling of each flavor per unit cell, we demonstrate the existence of STMIs which exhibit a quantized charge or spin Hall response. We first establish this phase in a bilayer Haldane-Hubbard model with localized orbitals on the $A$ sublattice and dispersive band on the $B$ sublattice. Starting from a trivial Mott insulator on the $A$ sublattice, tuning the sublattice potential drives a Bose-Einstein-condensation (BEC) to Bardeen-Cooper-Schrieffer (BCS) transition of the associated $p-\mathrm{i}p$ exciton pairing, realizing a topological Mott insulator with $C=1$ per flavor. We further generalize this construction to a single-layer spinful model, where the resulting STMI hosts charge edge modes coexisting with bulk local moments. A Mott semimetal is identified at the quantum critical point between the STMI and the trivial Mott insulator. Finally, we discuss applications to AA-stacked MoTe$_2$/WSe$_2$, proposing a ferromagnetic Chern insulator phase as a low-temperature descendant of the symmetric Mott semimetal.