Yoshikazu Suzumura

Confinement of interchain hopping by umklapp scattering in two coupled chains

The effect of umklapp scattering on interchain hopping has been investigated for two coupled chains of interacting electrons with a half-filled band. By analyzing in terms of the renormalization-group method, we have found that interchain hopping is renormalized to zero and is confined when a gap induced by umklapp scattering becomes larger than a critical value. From a phase diagram calculated on a plane of the interchain hopping and the gap, we discuss a role of the correlation gap that has been studied in the metallic state at temperatures above the spin-density-wave state in organic conductors.

Collective Modes of SDW with One-Dimensional Quarter-Filled Band

Fluctuations of both charge density and spin density around the mean-fields of the spin density wave (SDW) state have been studied by calculating collective modes in the case of one-dimensional quarter-filled band and arbitrary magnitude of the inter- action. It is shown that the coexistence of the 2 k F -SDW with the 4 k F -charge density wave is crucial for the commensurability energy and the collective mode of the density fluctuation.

Electronic states in half-filled correlated system with alternating potential

The effect of an alternating potential on a one-dimensional half-filled Hubbard model with repulsive interaction has been examined by applying the renormalization group method to the bosonized Hamiltonian. The electronic state, which is determined by the competition between alternating potential and umklapp scattering, is calculated where the relevance and the irrelevance of the alternating potential lead to the band insulator and the Mott insulator respectively. The excitation gaps for charge and spin fluctuations are calculated for both states.

Commensurate-incommensurate transition in two-coupled chains of nearly half-filled electrons

Abstract:We investigate the physical properties of two coupled chains of electrons, with a nearly half-filled band, as a function of the interchain hopping t⊥ and the doping. We show that upon doping, the system undergoes a metal-insulator transition well described by a commensurate-incommensurate transition. By using bosonization and renormalization we determine the full phase diagram of the system, and the physical quantities such as the charge gap. In the commensurate phase two different regions, for which the interchain hopping is relevant and irrelevant exist, leading to a confinement-deconfinement crossover in this phase. A minimum of the charge gap is observed for values of t⊥ close to this crossover. At large t⊥ the region of the commensurate phase is enhanced, compared to a single chain. At the metal-insulator transition the Luttinger parameter takes the universal value Kρ* = 1, in agreement with previous results on special limits of this model.

Strongly Correlated Electrons in Mixed-Valence Conductors DCNQI-Cu Salts

Organic conductors, DCNQI-Cu salts, with a mixed valence Cu +4/3 on the average has been studied theoretically by applying the slave-boson method to the strongly correlated systems which consist of π-electrons of DCNQI molecule and d-electrons of Cu atoms. The ground state is calculated by use of the 1/N σ expansion method which treats the local constraint strictly. It is shown that the electron mass around the Fermi surface is enhanced in the presence of the charge density with the three-fold periodicity.

Novel Phase Transition in Quarter-Filled SDW State with Dimerization

We have examined spin density wave (SDW) state in a quasi-one-dimensional electron system with both commensurability of quarter-filled band and dimerization, which compete with each other. It is shown that there are two kinds of critical temperatures: T c for the onset of the SDW state and T c2 (< T c ) for another phase at low temperatures, where both phase transitions are of the second order. The former is pure 2 k F -SDW and the latter is followed by 4 k F -charge density wave with Fermi momentum, k F .

Theoretical Study on the Charge Gap of Organic Conductor - Bechgaard Salts -

The charge gap in a quarter-filled organic conductor, which is induced by dimerization and/or alternating potential is studied by applying the renormalization group method to the bosonized one-dimensional Hamiltonian. The interplay of dimerization and alternating potential gives rise to the unconventional enhancement of the charge gap in addition to the on-site repulsive interaction. The experimental results of resistivity and optical conductivity in Bechgaard salts are examined based on the present calculation.

Peierls Transition of Strongly Correlated DCNQI-Cu Salts

The strongly correlated electronic states of the periodic Anderson model in the presence of the electron-phonon (e-p) interaction have been examined to understand the properties of the metal-insulator transition for DCNQI-Cu salts. By making use of the slave-boson mean-field theory based on the previous work [J. Phys. Soc. Jpn. 62 (1993) 3244], it is shown that the first-order Peierls transition from the metallic state with the heavy electron mass into the insulating state with the local spin takes place by varying the temperature and/or the e-p coupling constant.

Commensurate-Incommensurate Transition in SDW States of Quasi-One-Dimensional Organic Conductors

Spin density wave (SDW) state of a quasi-one-dimensional organic conductors near the quarter-filling has been examined in the presence of dimerization, which leads to properties of half-filling. By applying a transfer integral method to a single chain with molecular fields determined self-consistently, it has been shown that two kinds of commensurate states appear for a small misfit parameter due to a competition between the commensurability energy and the dimerization energy. Several phase diagrams of the commensurate state and the incommensurate state have been obtained as the function of misfit parameter, temperature and dimerization.

Collective modes and magnetic susceptibility of SDW state with one-dimensional half-filled band

The fluctuation around the molecular field of the spin density wave (SDW) state has been examined by calculating the collective modes and the spectral weight as a function of arbitrary strength of the repulsive on-site interaction, U , for a one-dimensional system with the half-filled band. The transverse mode is well described by the spin wave for both the small U and the large U and takes the spectral weight which is dominant compared with that of the longitudinal mode for the large U . The temperature dependence of the static magnetic susceptibility is calculated for both the longitudinal and transverse cases.