Renormalization-group approach to the metal-insulator transitions in (DCNQI)(2)M (DCNQI is N,N'-dicyanoquinonediimine and M=Ag, Cu)

Article

关键词: STRONGLY CORRELATED ELECTRONS;    ONE-DIMENSIONAL CONDUCTORS;    LONG-RANGE INTERACTION;    SPIN-GAP;    ORGANIC CONDUCTORS;    PHASE-DIAGRAM;    HUBBARD-MODEL;    MOLECULAR CONDUCTOR;    PHONON INTERACTION;    LUTTINGER-LIQUID;   

DOI  :  10.1103/PhysRevB.56.7262

来源: SCIE

【 摘 要 】

Metal-insulator transitions and different ground-state phases in the quasi-one-dimensional materials, (R1R2-DCNQI)(2)M (R-1 = R-2 = CH3, I and M = Ag, Cu), are studied with a renormalization-group method. We use one-dimensional continuum models with backward scatterings, umklapp processes, and couplings with 2k(F) and 4k(F) phonons (not static lattice distortion). We take a quarter-filled band for M = Ag and a sixth-filled band coupled with a third-filled band for M = Cu. Depending on electron-electron and electron-phonon coupling strengths, the ground-state phase becomes a Tomonaga-Luttinger liquid or a state with a gap(s). For M = Ag, there appears a spin-gap state with a dominant 2k(F) charge-density-wave correlation, a Mott insulator with a dominant 4k(F) charge-density-wave correlation, or a spin-Peierls state with different magnitudes of spin and charge gaps. Three dimensionality is taken into account by cutting off the logarithmic singularity in either the particle-particle channel or the particle-hole channel. The difference between the ground-state phase of the R-1 = R-2 = CH3 salt (spin-Peierls state) and that of the R-1 = R-2 = I salt (antiferromagnetic state) is qualitatively I explained by a difference in the cutoff energy in the particle-particle channel. For M = Cu, there appears a Mott insulator with a charge-density wave of period 3 and a Peierls insulator with a charge-ensity wave of period 6. The conditions for the experimentally observed, Mott insulator phase are strong correlation in the sixth-filled band, moderate electron-phonon couplings, and finite electron-4k(F) phonon coupling. Resistance is calculated as a function of temperature with a memory-function approximation in both cases above. It qualitatively reproduces the differences among the M = Ag and M = Cu cases as well as the R-1 = R-2 = CH3 and R-1 = R-2 = I cases.

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