Fractional spin fluctuations and quantum liquid signature in Gd2ZnIrO6

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, ${\mathrm{Gd}}_{2}{\mathrm{ZnIrO}}_{6}$, as a function of different incident photon energies and polarization in a broad temperature range. Our results evidence the spin fractionalization within the paramagnetic phase reflected in the emergence of a polarization-independent quasielastic 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 quantum fluctuations. This anomalous scattering response is thus indicative of fluctuating fractional spin evincing the proximate quantum spin liquid phase in a three-dimensional double-perovskite system.