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 phenomenon could be tested in materials such as triangular lattice organics, three-dimensional mixed valence insulators ${\mathrm{YbB}}_{12}$ and ${\mathrm{SmB}}_6$, and transition metal dichalcogenides 1T-${\mathrm{TaS}}_2$ and 1T-${\mathrm{TaSe}}_2$.

• Received 25 May 2019
• Revised 16 October 2019

DOI:https://doi.org/10.1103/PhysRevB.100.155150