Unconventional resistivity at the border of metallic antiferromagnetism in NiS2

We report low-temperature and high-pressure measurements of the electrical resistivity rho(T) of the antiferromagnetic compound NiS2 in its high-pressure metallic state. The form of rho(T,p) suggests the presence of a quantum phase transition at a critical pressure p(c)= 76 +/- 5 kbar. Near pc, the temperature variation of rho(T) is similar to that observed in NiS2-xSex near the critical composition x= 1, where metallic antiferromagnetism is suppressed at ambient pressure. In both cases, rho(T) varies approximately as T-1.5 over a wide range below 100 K. This lets us assume that the high-pressure metallic phase of stoichiometric NiS2 also develops itinerant antiferromagnetism, which becomes suppressed at p(c). However, on closer analysis, the resistivity exponent in NiS2 exhibits an undulating variation with temperature not seen in NiSSe(x=1). This difference in behavior may be due to the effects of spin-fluctuation scattering of charge carriers on cold and hot spots of the Fermi surface in the presence of quenched disorder, which is higher in NiSSe than in stoichiometric NiS2.