Exciton-roton mode in moir\'e fractional Chern insulators

TL;DR

This paper predicts a novel exciton-roton mode in moiré fractional Chern insulators arising from hybridization of excitations, which can be detected via optical spectroscopy.

Contribution

It introduces the exciton-roton mode resulting from hybridization of magneto-roton and interband excitations in moiré FCIs, highlighting optical spectroscopy as a probing tool.

Findings

Hybridization controls the exciton-roton mode in twisted MoTe2.

The exciton-roton mode has a lower energy than interband transitions.

Optical activity of the mode produces a double-peak spectroscopic signature.

Abstract

Moir\'e fractional Chern insulators (FCIs) are a novel class of quantum matter that realizes fractional quantum Hall (FQH) physics in zero magnetic field and provides a platform for exploring unconventional collective excitations. Here we show that hybridization between the magneto-roton and moir\'e interband excitations gives rise to an exciton-roton mode absent in continuum FQH systems in the long-wavelength limit. Using exact diagonalization and a variational Bethe-Salpeter equation for twisted MoTe$_2$, we demonstrate that this hybridization is controlled by the quantum geometry and yields a mode that combines excitonic optical response with the characteristic FCI roton minimum. The resulting exciton-roton remains low-lying, with excitation energy below the interband transition, and acquires optical activity, leading to a double-peak spectroscopic signature. These results identify optical spectroscopy as a direct probe of collective excitations in moir\'e FCIs.