  Quantum spin liquid (QSL) has become an exciting topic in interacting spin
systems that do not order magnetically down to the lowest experimentally
accessible temperature; however, conclusive experimental evidence remains
lacking. Motivated by the recent surge of theoretical and experimental interest
in a half-filled Hubbard model on the triangular lattice, where chiral QSL can
be stabilized, we investigate the electromagnetic signature of the chiral QSL
to aid experimental detection. We systematically studied the electrical charge
and orbital electrical current associated with a spinon excitation in the
chiral QSL based on parton mean-field theory and unbiased density-matrix
renormalization group calculations. We then calculated both longitudinal and
transverse optical conductivities below the Mott gap. We also conduct quantum
field theory analysis to unravel the connection between spinon excitation and
emergent and physical gauge fields. Our results show that the chiral QSL phase
has a clear electromagnetic response even in a Mott insulator regime, which can
facilitate the experimental detection of this long-sought-after phase.
