Quantum critical behavior in the organic conductor κ-(DHDA-TTP)2SbF6

Temperature–pressure phase diagram of the 2-D organic conductor, κ-(DHDA-TTP)2SbF6 (DHDA-TTP = 2-(1,3-dithiolan-2-ylidene)-5-(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene) is presented. This phase diagram exhibits a pressure boundary between insulator and Fermi liquid (FL). This boundary is considered as a critical pressure of quantum fluctuation between probable charge ordering and FL ground states. In the vicinity of the specific pressure, divergence of the prefactor A in ρ = ρ0 + AT2, is observed, where ρ is the in-plane resistivity and T is the temperature. Following the similar phase diagram to κ-(MeDH-TTP)2AsF6 by Yasuzuka et al., this is the second example in the two-dimensional 1/4-filled organic conductors, showing the temperature–pressure phase diagram of quantum critical behavior. It is remarkable that this kind of divergence of A at certain critical point is rather general phenomena at least in these 1/4-filled 2-D organic conductors, in contrast to the other 1/2-filled κ-type organic conductors, which show Kanodaʹs phase diagram with Mott insulator and superconductor.