Electromagnetic response and emergent topological orders in transition metal dichalcogenide MoTe$_2$ bilayers

TL;DR

This paper explores how magnetic and electric fields influence the topological electronic phases in twisted bilayer MoTe$_2$, revealing fractional Chern insulators and phase transitions through a detailed Hofstadter spectrum analysis.

Contribution

It introduces a continuum model with second harmonic moiré potentials to analyze topological orders and fractional Chern insulators in twisted MoTe$_2$ under external fields.

Findings

Identification of Landau fan structures in Hofstadter spectra.

Observation of both Jain-sequence and higher Chern number FCIs.

Electric field-induced topological phase transitions.

Abstract

Twisted bilayer transition metal dichalcogenides, such as MoTe$_2$, provide a versatile platform for exploring correlated topological phases. This work investigates the interplay of perpendicular magnetic and electric fields in tuning the electronic structure and emergent topological orders of twisted bilayer MoTe$_2$ (t-MoTe$_2$) across two distinct regimes: a low-twist-angle phase ($\theta\approx2.1^\circ$) hosting multiple Chern bands of identical Chern numbers per valley, and a higher-angle phase ($\theta\approx 3.89^\circ$) featuring Haldane-like bands with opposite Chern numbers. Using a continuum model incorporating moir\'e potentials up to second harmonics, we compute the Hofstadter fractal spectra under applied fields, revealing Landau fan structures and magnetic-flux-dependent band topology. These fractal spectra are useful in studying emergent topological orders in terms of the composite fermion picture, where the statistical Chern-Simons flux is approximated as a uniform gauge field. We demonstrate that the system hosts both Jain-sequence fractional Chern insulators (FCIs) and non-Jain "fractal FCIs" with higher Chern numbers. The electric field suppresses composite fermion gaps and induces topological quantum phase transitions. Furthermore, our analysis extends to valley-contrasting flux attachment, proposing pathways to describe fractional quantum spin Hall states.