Interaction Driven Topological Phase Transition in Monolayer CrCl$_2$(pyrazine)$_2$

TL;DR

This paper predicts that a monolayer of CrCl$_2$(pyrazine)$_2$, a layered metal-organic framework, can host interaction-driven topological and nematic phases, including a quantum anomalous Hall state, based on theoretical phase diagram analysis.

Contribution

It introduces a theoretical phase diagram for monolayer CrCl$_2$(pyrazine)$_2$, revealing potential for realizing exotic topological and nematic states driven by electron interactions.

Findings

Identification of a QAH phase stabilized by interactions.

Discovery of nematic insulator and Dirac semimetal states.

QAH state robustness and tunability prospects.

Abstract

The quadratic band crossing points (QBCPs) at Fermi level in two-dimension have been proposed to be unstable under electron-electron interaction. The possible interaction driven states include quantum anomalous Hall (QAH) state and various nematic ordered states. In this work, motivated by the discovery of ferromagnetic van der Waals layered metal-organic framework CrCl$_2$(pyrazine)$_2$, we theoretically propose that the single layer of CrCl$_2$(pyrazine)$_2$ might realize one or some of these interaction driven states based on the QBCP protected by $C_4$ symmetry. By introducing the short-range density-density type repulsion interactions into this system, we have found the phase diagram depending on different interaction range and strength. The exotic phases include the staggered chiral flux state manifesting QAH effect, the site-nematic insulator and the site-nematic Dirac semimetal state. The QAH state is robust against perturbations breaking the QBCP but it is weakened by increasing temperature. The metal-organic framework is tunable by changing the transition-metal elements, which might improve the gap size and stability of this interaction induced QAH state.