Quantum criticality at a Mott-Hubbard Metal-Insulator Transition

The Mott insulator nickel disulfide undergoes an insulator to metal transition that can be driven by either hydrostatic pressure or doping-induced chemical pressure. Previously,NiS2~doped with selenium to just below the quantum critical point showed anomalous critical exponents as a function of pressure. Doping, however, introduces positional disorder and charge transfer effects from the selenium orbitals, potentially altering the critical behavior. We report here on a set of transport experiments on pure~NiS2, where the pressure and temperature scales for the critical regime require the use of a diamond anvil cell integrated with a helium dilution refrigerator, allowing us to compare the critical behavior of the pure and doped materials.