T. Itou

Magnetic-field-induced Mott transition in a quasi-two-dimensional organic conductor.

We investigated the effect of magnetic field on the highly correlated metal near the Mott transition in the quasi-two-dimensional layered organic conductor, kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl, by the resistance measurements under control of temperature, pressure, and magnetic field. It was demonstrated that the marginal metallic phase near the Mott transition is susceptible to the field-induced localization transition of the first order, as was predicted theoretically. The thermodynamic consideration of the present results gives a conceptual pressure-field phase diagram of the Mott transition at low temperatures.

Slow dynamics of electrons at a metal–Mott insulator boundary in an organic system with disorder

NMR captures unusual slow dynamics of electrons on Mott transition with disorder, suggesting an electronic Griffiths phase. The Mott transition—a metal-insulator transition caused by repulsive Coulomb interactions between electrons—is a central issue in condensed matter physics because it is the mother earth of various attractive phenomena. Outstanding examples are high–Tc (critical temperature) cuprates and manganites exhibiting colossal magnetoresistance. Furthermore, spin liquid states, which are quantum-fluctuation–driven disordered ground states in antiferromagnets, have recently been found in magnetic systems very near the Mott transition. To date, intensive studies on the Mott transition have been conducted and appear to have established a nearly complete framework for understanding the Mott transition. We found an unknown type of Mott transition in an organic spin liquid material with a slightly disordered lattice. Around the Mott transition region of this material under pressure, nuclear magnetic resonance experiments capture the emergence of slow electronic fluctuations of the order of kilohertz or lower, which is not expected in the conventional Mott transition that appears as a clear first-order transition at low temperatures. We suggest that they are due to the unconventional metal-insulator fluctuations emerging around the disordered Mott transition in analogy to the slowly fluctuating spin phase, or Griffiths phase, realized in Ising spin systems with disordered lattices.

Electronic state of (DI-DCNQI)2Ag with Cu doping or under pressure

(DI-DCNQI) 2 Ag, which has a quasi-one-dimensional quarter-filled π band, is a charge-ordered insulator. In the present study, the charge-ordered phase has been melted in two ways and characterized by the resistivity measurements. One is Cu doping into the Ag sites and the other is application of pressure. As the Cu content is increased, the charge-gapped insulator changes to the nongapped insulator with the variable range hopping behaviour, eventually followed by the metallic phase. When (DI-DCNQI) 2 Ag is pressurized, clear metallic behaviours appear in resistivity above the metal-insulator transition, the temperature of which is decreased at elevated pressures.

Electronic state of (DI-DCNQI)2Ag under ambient and applied pressures

Abstract The resistivity and susceptibility of (DI-DCNQI)2Ag were found to show anomalies corresponding to the charge ordering and the antiferromagnetic transition, respectively, at ambient pressure. The 13 C NMR measurements evidenced that the charge ordering is depressed toward the lower temperatures by application of pressure.