  Quantum spin liquids (QSLs) are highly entangled, disordered magnetic states
that arise in frustrated Mott insulators and host exotic fractional excitations
such as spinons and chargons. Despite being charge insulators some QSLs are
predicted to exhibit gapless itinerant spinons that yield metallic behavior in
the spin channel. We have deposited isolated magnetic atoms onto single-layer
(SL) 1T-TaSe$_2$, a gapless QSL candidate, to experimentally probe how
itinerant spinons couple to impurity spin centers. Using scanning tunneling
spectroscopy we observe the emergence of new, impurity-induced resonance peaks
at the 1T-TaSe$_2$ Hubbard band edges when cobalt adatoms are positioned to
have maximal spatial overlap with the Hubbard band charge distribution. These
resonance peaks disappear when the spatial overlap is reduced or when the
magnetic impurities are replaced with non-magnetic impurities. Theoretical
simulations using a modified Anderson impurity model integrated with a gapless
quantum spin liquid show that these resonance peaks are consistent with a Kondo
resonance induced by spinons combined with spinon-chargon binding effects that
arise due to QSL gauge-field fluctuations.
