  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$_2$.
