  Hitherto, the discrete identification of quantum spin liquid phase, holy
grail of condensed matter physics, remains a challenging task experimentally.
However, the precursor of quantum spin liquid state may reflect in the spin
dynamics even in the paramagnetic phase over a wide temperature range as
conjectured theoretically. Here we report comprehensive inelastic light (Raman)
scattering measurements on the Ir based double perovskite, Gd2ZnIrO6, as a
function of different incident photon energies and polarization in a broad
temperature range. Our results evidenced the spin fractionalization within the
paramagnetic phase reflected in the emergence of a polarization independent
quasi-elastic peak at low energies with lowering temperature. Also, the
fluctuating scattering amplitude measured via dynamic Raman susceptibility
increases with lowering temperature and decreases mildly upon entering into
long-range magnetic ordering phase, below 23 K, suggesting the magnetic origin
of these fluctuations. This anomalous scattering response is thus indicative of
fluctuating fractional spin evincing the quantum spin liquid phase in a
three-dimensional double perovskite system.
