A quantum critical point (QCP) between the antiferromagnetic and the paramagnetic phases was realized by applying a hydrostatic pressure of ~ 7 GPa on single crystals of NiS_{ 2} pyrite with a low residual resistivity, rho_{ 0}, of 0.5 mu-Omega-cm. We found that the critical behavior of the resistivity, rho, in this clean system contrasts sharply with those observed in its disordered analogue, NiS_{ 2-x}Se_{ x} solid-solution, demonstrating the unexpectedly drastic effect of disorder on the quantum criticality. Over a whole paramagnetic region investigated up to P = 9 GPa, a crossover temperature, defined as the onset of T^{ 2} dependence of rho, an indication of Fermi liquid, was suppressed to a substantially low temperature T sim 2 K and, instead, a non Fermi liquid behavior of rho, T^{ 3/2}-dependence, robustly showed up.
Categories: cond-mat.str-el