arXiv subjects

Yoshikazu Suzumura

Publications and source records attributed to Yoshikazu Suzumura.

At least 55 records · Page 3Linked to original sources

arXiv2009

Electronic Properties Close to Dirac Cone in Two-Dimensional Organic Conductor $α$-(BEDT-TTF)$_2$I$_3$

A zero-gap state (ZGS) has been found in a bulk system of two-dimensional organic conductor, $α$-(BEDT-TTF)$_2$I$_3$ salt which consists of four sites of donor molecules in a unit cell. In the present paper, the characteristic of the ZGS is analyzed in detail and the electronic properties are examined in the vicinity of the contact point where the conduction and valence bands degenerate to form the zero-gap. The eigenvectors of the energy band have four components of respective sites, where two of them correspond to inequivalent sites and the other two correspond to equivalent sites. It is shown that the former exhibits an exotic momentum dependence around the contact point and the latter shows almost a constant dependence. The density of states of each site close to the Fermi point is calculated to demonstrate the temperature dependence of the local magnetic susceptibility and the local nuclear magnetic relaxation rate. Further, the robust property of the ZGS against the anion potential is also shown by using the second-order perturbation.

cond-mat.str-el↗

arXiv2007

Role of Interlayer Electron Hopping for Spin Density Wave State in the Zero-Gap Organic Conductor

We investigate the formation of density waves in the zero-gap state (ZGS) which has been found in the quasi-two-dimensional organic conductor $α$-(BEDT-TTF)$_2$I$_3$ salt under the hydrostatic pressure. The ZGS exhibits the cone-like dispersion for both the conduction band and the valence band which degenerate each other at the two-dimensional wave vectors, $\pm\mib{k}_0$ forming a zero gap. By using the extended Hubbard model with repulsive interaction we calculate the onset temperature of the spin density wave (SDW) as a function of the interlayer electron hopping, which by itself does not break the cone-like dispersion. It is shown that the SDW with wave number $2\mib{k}_0$ is induced by the combined effect of the interaction, the inter-band excitation across the zero-gap and the interlayer hopping.

cond-mat.str-el↗

arXiv2007

Role of Interchain Hopping in the Magnetic Susceptibility of Quasi-One-Dimensional Electron Systems

The role of interchain hopping in quasi-one-dimensional (Q-1D) electron systems is investigated by extending the Kadanoff-Wilson renormalization group of one-dimensional (1D) systems to Q-1D systems. This scheme is applied to the extended Hubbard model to calculate the temperature ($T$) dependence of the magnetic susceptibility, $χ(T)$. The calculation is performed by taking into account not only the logarithmic Cooper and Peierls channels, but also the non-logarithmic Landau and finite momentum Cooper channels, which give relevant contributions to the uniform response at finite temperatures. It is shown that the interchain hopping, $t_\perp$, reduces $χ(T)$ at low temperatures, while it enhances $χ(T)$ at high temperatures. This notable $t_\perp$ dependence is ascribed to the fact that $t_\perp$ enhances the antiferromagnetic spin fluctuation at low temperatures, while it suppresses the 1D fluctuation at high temperatures. The result is at variance with the random-phase-approximation approach, which predicts an enhancement of $χ(T)$ by $t_\perp$ over the whole temperature range. The influence of both the long-range repulsion and the nesting deviations on $χ(T)$ is further investigated. We discuss the present results in connection with the data of $χ(T)$ in the (TMTTF)$_2X$ and (TMTSF)$_2X$ series of Q-1D organic conductors, and propose a theoretical prediction for the effect of pressure on magnetic susceptibility.

cond-mat.str-el↗

arXiv2006

Pressure-Induced Zero-Gap Semiconducting State in Organic Conductor $α$-(BEDT-TTF)$_2$I$_3$ Salt

We show a zero-gap semiconducting (ZGS) state in the quasi-two-dimensional organic conductor $α$-(BEDT-TTF)$_2$I$_3$ salt, which emerges under uniaxial pressure along the a-axis (the stacking axis of the BEDT-TTF molecule). The ZGS state is the state in which a Dirac cone with the band spectrum of a linear dispersion exists around the Fermi point connecting an unoccupied (electron) band with an occupied (hole) band. The spectrum exhibits a large anisotropy in velocity, which depends on the direction from the Fermi point. By varying the magnitude of several transfer energies of a tight-binding model with four sites per unit cell, it is shown that the ZGS state exists in a wide pressure range, and is attributable to the large anisotropy of the transfer energies along the stacking axis.

cond-mat.mtrl-sci↗

arXiv2006

Electric Conductivity of the Zero-gap Semiconducting State in Alpha-(BEDT-TTF)2I3 Salt

The electric conductivity which reveals the zero gap semiconducting (ZGS) state has been investigated as the function of temperature $T$ and life time $τ$ in order to understand the ZGS state in quarter-filled $α$-(BEDT-TTF)$_2$I$_3$ salt with four sites in the unit cell. By treating $τ$ as a parameter and making use of the one-loop approximation, it is found that the conductivity is proportional to $T$ and $τ$ for $k_B\gg\hbar/τ$ and independent of $T$ and $τ$ for $k_B T\ll\hbar/τ$. Further the conductivity being independent of $T$ in the ZGS state is examined in terms of Born approximation for the impurity cattering.

cond-mat.mtrl-sci↗

arXiv2005

Effect of Inter-Site Repulsions on Magnetic Susceptibility of One-Dimensional Electron Systems at Quarter-Filling

The temperature dependence of the magnetic susceptibility, χ(T), is investigated for one-dimensional interacting electron systems at quarter-filling within the Kadanoff-Wilson renormalization-group method. The forward scattering on the same branch (the g_4-process) is examined together with the backward (g_1) and forward (g_2) scattering amplitudes on opposite branches. In connection with lattice models, we show that χ(T) is strongly enhanced by the nearest-neighbor interaction, an enhancement that surpasses one of the next-nearest-neighbor interaction. A connection between our predictions for χ(T) and experimental results for χ(T) in quasi-one-dimensional organic conductors is presented.

cond-mat.str-el↗

arXiv2003

Charge fluctuation induced superconducting state in two-dimensional quarter-filled electron systems

We investigate the superconducting (SC) state in two-dimensional extended Hubbard model at a quarter-filling with the on-site repulsive interaction ($U$) and the nearest-neighbor one ($V$), which lead to the spin fluctuation and the charge fluctuation, respectively. The effect of the charge fluctuation on the onset of the SC state is calculated by estimating the pairing interaction within the random phase approximation. Solving the linearized Eliashberg equation with the anomalous self-energy as the function of both momentum and frequency, we examined the singlet SC state on the plane of $U$ and $V$ with the fixed temperature. We found a novel result that the SC state with the $d_{xy}$ symmetry retains for most parameters of $U$ and $V$, although the pairing interaction changes the sign from repulsive one into attractive one with increasing $V$. The reentrant transition as the function of temperature occurs close to the onset of the SC state.

cond-mat.supr-con↗

arXiv2003

On the Mott glass in the one-dimensional half-filled charge density waves

We study the effect of impurity pinning on a one-dimensional half-filled electron system, which is expressed in terms of a phase Hamiltonian with the charge degree of freedom. Within the classical treatment, the pinned state is examined numerically. The Mott glass, which has been pointed out by Orignac et al. [Phys. Rev. Lett 83 (1999) 2378], appears in the intermediate region where the impurity potential competes with the commensurate potential. Such a state is verified by calculating the soliton formation energy, the local restoring force around the pinned state and the optical conductivity.

cond-mat.str-el↗

arXiv2003

Competition of Dimerization and Charge Ordering in the Spin-Peierls State of Organic Conductors

The effect of the charge ordering on the spin-Peierls (SP) state has been examined by using a Peierls-Hubbard model at quarter-filling with dimerization, on-site and nearest-neighbor repulsive interactions. By taking account of the presence of dimerization, a bond distortion is calculated variationally with the renormalization group method based on bosonization. When the charge ordering appears at V=V_c with increasing the nearest-neighbor interaction (V), the distortion exhibits a maximum due to competition between the dimerization and the charge ordering. It is shown that the second-order phase transition occurs from the SP state with the bond alternation to a mixed state with an additional component of the site alternationat V = V_c.

cond-mat.str-el↗

arXiv2002

Role of Collective Mode for Optical Conductivity and Reflectivity in Quarter-Filled Spin-Density-Wave State

Taking account of a collective mode relevant to charge fluctuation, the optical conductivity of spin-density-wave state has been examined for an extended Hubbard model with one-dimensional quarter-filled band. We find that, within the random phase approximation, the conductivity exhibits several peaks at the frequency corresponding to the excitation energy of the commensurate collective mode. When charge ordering appears with increasing inter-site repulsive interactions, the main peak with the lowest frequency is reduced and the effective mass of the mode is enhanced indicating the suppression of the effect of the collective mode by charge ordering. It is also shown that the reflectivity becomes large in a wide range of frequency due to the huge dielectric constant induced by the collective mode.

cond-mat.str-el↗

arXiv2002

Correlation Effect on Peierls Transition

The effect of correlation on Peierls transition, which is accompanied by a dimerization, t_d, of a bond alternation for transfer energy, has been examined for a half-filled one-dimensional electron system with on-site repulsive interaction (U). By applying the renormalization group method to the interaction of the bosonized Hamiltonian, the dimerization has been calculated variationally and self-consistently with a fixed electron-phonon coupling constant (λ) and it is shown that t_d takes a maximum as a function of U. The result is examined in terms of charge gap and spin gap and is compared with that of the numerical simulation by Hirsch [Phys. Rev. Lett 51 (1983) 296]. Relevance to the spin Peierls transition in organic conductors is discussed.

cond-mat.str-el↗

arXiv2001

Crossover from Quarter-Filling to Half-Filling in a One-Dimensional Electron System with a Dimerized and Quarter-Filled Band

The interplay between quarter-filled and half-filled umklapp scattering has been examined by applying the renormalization group method to a one-dimensional quarter-filled electron system with dimerization, on-site (U) and nearest-neighbor (V) repulsive interactions. The phase diagram on the U-V plane is obtained at absolute zero temperature where the Mott insulator (the charge ordered insulator) is found for smaller (larger) V. By choosing the moderate parameter in the region of Mott insulator, it is shown that the resistivity exhibits a crossover from behavior of quarter-filling to that of half-filling with decreasing temperature.

cond-mat.str-el↗

arXiv2000

Role of Phase Variables in Quarter-Filled Spin Density Wave States

Several kinds of spin density wave (SDW) states with both quarter-filled band and dimerization are reexamined for a one-dimensional system with on-site, nearest-neighbor and next-nearest-neighbor repulsive interactions, which has been investigated by Kobayashi et al. (J. Phys. Soc. Jpn. 67 (1998) 1098). Within the mean-field theory, the ground state and the response to the density variation are calculated in terms of phase variables, $θ$ and $ϕ$, where $θ$ expresses the charge fluctuation of SDW and $ϕ$ describes the relative motion between density wave with up spin and that with down spin respectively. It is shown that the exotic state of coexistence of 2k_F-SDW and 2k_F-charge density wave (CDW) is followed by 4k_F-SDW but not by 4k_F-CDW where k_F denotes a Fermi wave vector. The harmonic potential with respect to the variation of $θ$ and/or $ϕ$ disappears for the interactions, which lead to the boundary between the pure 2k_F-SDW state and the corresponding coexistent state.

cond-mat.str-el↗

arXiv2000

Quarter-filled spin density wave states with long-range Coulomb interaction

Spin density wave (SDW) states at quarter-filling, which coexist with charge density wave (CDW) states, have been examined where the critical temperature is calculated for an extended Hubbard model with long range repulsive interactions. Within the mean-field theory, it is shown that the first order transition occurs with decreasing temperature for interactions located around the boundary between SDW state and CDW state.

cond-mat.str-el↗

arXiv2000

Correlation Effects in a One-Dimensional Quarter-Filled Electron System with Repulsive Interactions

A one-dimensional electron system at quarter-filling has been examined by applying the renormalization group method to a bosonized model with on-site (U) and nearest-neighbor (V) repulsive interactions. By evaluating both normal scattering and Umklapp scattering perturbatively, we obtain a phase diagram in which a metallic state with a 2k_F spin density wave (k_F is the Fermi wave number) moves into an insulating state with charge disproportionation of a 4k_F charge density wave with an increase in both U and V. The effect of the next-nearest-neighbor repulsion is also discussed.

cond-mat.str-el↗

arXiv1999

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 leads to the band insulator and the Mott insulator respectively. The excitation gaps for charge and spin fluctuations are calculated for both states.

cond-mat.str-el↗

arXiv1998

Two-Coupled Chains with Spin-Anisotropic Backward Scattering

By applying renormalization group method to the bosonized Hamiltonian of two-coupled chains with repulsive intrachain interaction, we have examined a role of backward scattering with a spin-anisotropy which competes with interchain hopping. From calculation of a dominant state in the limit of low energy, it is found that superconducting state moves into spin density wave state when the anisotropy becomes larger than a critical value. Further phase diagram is shown on the plane of g-ology.

cond-mat.str-el↗

arXiv1997

Crossover between High and Low Energy-States in Two-Coupled Chains of Tomonaga Model

By applying the renormalization group method to two-coupled chains in the Tomonaga model, the role of interchain hopping has been studied in the entire energy region. The energy for a crossover from the perturbational regime to the relevant regime becomes smaller than that of the interchain hopping due to one-dimensional fluctuations of the mutual interaction. From the calculation of response functions for charge density waves and superconducting states, the phase diagram of dominant and subdominant states has been obtained in the plane of mutual interactions with fixed energy.

cond-mat.str-el↗