# Cyclotron resonance inside the Mott gap: a fingerprint of emergent neutral fermions

## TL;DR

This paper proposes an optoelectronic method to detect spin-charge separated states with neutral fermions in correlated materials by observing unique cyclotron resonance features in their light absorption spectra.

## Contribution

It introduces a novel experimental approach to identify exotic quantum phases with neutral fermions using cyclotron resonance in materials with spin-charge separation.

## Key findings

- Neutral fermion states show cyclotron resonance peaks despite insulating behavior.
- The absence of the principal Kohn mode distinguishes these states from ordinary metals.
- Applicable to various materials like YbB$_{12}$, SmB$_6$, and transition metal dichalcogenides.

## Abstract

A major obstacle to identify exotic quantum phases of matter featuring spin-charge separation above one-dimension is the lack of tailored probes allowing to establish their presence in correlated materials. Here we propose an optoelectronic response that could allow to pinpoint the presence of certain spin-charge separated states with emergent neutral gapless fermions in two and three-dimensional materials. We show that even though these states behave like insulators under static electric fields, they can display clear cyclotron resonance peaks in their light absorption spectrum under static magnetic fields, but typically the principal Kohn mode will be missing in comparison to ordinary metals. This distinctive phenomena could be tested in materials such as triangular lattice organics, three-dimensional mixed valence insulators YbB$_{12}$ and SmB$_6$, and transition metal dichalcogenides 1T-TaS$_2$ and 1T-TaSe$_2$.