Impurities induced Mott insulating state revealed by magneto-optical spectrum

Insulator-metal transition IMT) that accompanied by huge resistivity change is one of the most studied phenomena in condensed matter physics area. While there are many observations of IMT upon tuning of the one-electron bandwidth W or band filling by doping, there are few reports of the opposite i.e., of the formation of a Mott-like insulating state upon the addition of impurities in a metal. One example of such impurity induced Mott transition is found in Cr doped V₂O₃. Another is the Mn or Ti doped Ruddleson-Popper-type layered ruthenates. Common features of these two systems include the widespread phase separation regions and strong lattice-orbital coupling. In this talk, we present the temperature and magnetic field dependent heat capacity and optical spectral measurements. We established two types of phase separation regions vary with magnetic field or doping concentration. Strong enhancement of both sommerfeld coefficient γ and long-wavelength excitation coefficient B were observed in the phase separation regions. Ferro-orbital-ordering, as well as lattice softening were observed in the Mott insulating state. These studies confirmed our previous proposed d⁰/d³ rule and the lattice-orbital coupling assisted mechanism for the impurities induced Mott transitions.