  NiPS3 is a Van der Waals antiferromagnet that has been found to display
spin-charge and spin-phonon coupling in its antiferromagnetically ordered state
below TN = 155 K. Here, we study high-quality crystals of site-diluted
Ni1-xZnxPS3 (0 < x < 0.2) using temperature-dependent specific heat and Raman
spectroscopy probes. The site dilution suppresses the antiferromagnetic
ordering in accordance with the mean-field prediction. In NiPS3, we show that
the phonon mode P2 (176 cm-1) associated with Ni vibrations show a distinct
asymmetry due to the Fano resonance, which persists only in the paramagnetic
phase, disappearing below T_N = 155 K. This was further supported by
temperature-dependent Raman data on an 8% Zn-doped crystal (T_N = 135 K) where
Fano resonance similarly van in the magnetically ordered phase. This is
contrary to the behaviour of the Raman mode P9 (570 cm-1), which shows a Fano
resonance at low temperatures below T_N due to its coupling with the two-magnon
continuum. We show that the Fano resonance of P2 arises from its coupling with
an electronic continuum that weakens considerably upon cooling to low
temperatures. In the doped crystals, the Fano coupling is found to enhance with
Zn-doping. These observations suggest the presence of strong electron-phonon
coupling in the paramagnetic phase of NiPS3 due to charge density fluctuations
associated with the negative charge transfer state of Ni.
