Electron transport near the 2D mott transition

Mutual interactions between electrons afford various kinds of exotic electronic phases such as high-T_c superconductivity, unconventional magnetism, colossal magnetoresistance, and so on (Imada et al., 1998). The interaction is represented by the Coulomb repulsive energy for two electrons accommodated by a site, which is called the on-site Coulomb energy U. On the other hand, electrons tend to propagate as Bloch waves on a periodic lattice owing to the wave-like nature by gaining quantum-mechanical kinetic energy characterized by the electronic bandwidth W. In the simple case of a half-filled band, the competition between the Coulomb energy and kinetic energy causes a metal-insulator transition; that is, the Mott transition. For W ⪢ U, electrons behave itinerant with the double occupation allowed, whereas for W ⪡ U, electrons keep staying at each site to avoid the double occupation. A dramatic metal- insulator transition (the Mott transition) is expected to occur when W ≈ U as the interaction-induced imbalance between the wave and particle natures. This phenomenon is one of the most prominent manifestations of the electron correlation in condensed matters and has long been studied since Mott’s argument on the insulating state of NiO₂ (Mott, 1990). The Mott transition is recognized as a key concept for understanding diverse interaction-induced emergent phenomena.