One-dimensional Half-filled Band Research Articles

Charge-density-wave formation in a half-filled fermion-boson transport model: A projective renormalization approach

We study the metal-insulator transition in a very general two-channel transport model, where charge carriers are coupled to a correlated background medium. The fluctuations of the background were described as bosonic excitations, having the ability to relax. Employing an analytical projector-based renormalization technique, we calculate the ground-state and spectral properties of this fermion-boson model and corroborate recent numerical results, which indicate---in dependence on the `stiffness' of the background medium---a Luttinger-liquid to charge-density-wave transition for the one-dimensional half-filled band case. In particular, we determine the renormalized electron and boson dispersion relations and show that the quantum phase transition is not triggered by a softening of the boson modes. Thus the charge density wave is different in nature from an usual Peierls distorted state.

One-dimensional quantum transport affected by a background medium: Fluctuations versus correlations

We analyze the spectral properties of a very general two-channel fermion-boson transport model in the insulating and metallic regimes, and the signatures of the metal-insulator quantum phase transition in between. To this end we determine the single particle spectral function related to angle-resolved photoemission spectroscopy, the momentum distribution function, the Drude weight and the optical response by means of a dynamical (pseudo-site) density-matrix renormalization group technique for the one-dimensional half-filled band case. We show how the interplay of correlations and fluctuations in the background medium controls the charge dynamics of the system, which is a fundamental problem in a great variety of advanced materials.

Metallization of (TTM-TTP)I3with a Highly One-Dimensional Half-Filled Band under Extremely High Pressure

The title compound (TTM-TTP)I 3 with a highly one-dimensional (1D) half-filled energy band is almost metallized by the application of pressure beyond 7 GPa. It is theoretically predicted that the g...

Anomalous Metallic State in (TTM-TTP)I3 with a Highly One-Dimensional Half-Filled Band under Pressure beyond 7 GPa

We demonstrate that the title compound (TTM-TTP)I3 with a highly one-dimensional half-filled band, which shows a metal-insulator (MI) transition around TMI=120 K, is metallized by application of extremely high pressure (P>7 GPa) using the cubic anvil apparatus. Above 5.7 GPa, the metallic behavior is described by {\(\rho \sim T^\alpha \)} with α ∼ 0.3 which is much smaller than the expected value of Fermi liquid theory, α=2. Based on these findings, the driving force of the MI transition is discussed.

Anomalous metallic state in (TTM-TTP)I3 with a highly one-dimensional half-filled band under pressure beyond 7 GPa

Anomalous metallic state in (TTM-TTP)I3 with a highly one-dimensional half-filled band under pressure beyond 7 GPa

Formula omitted]-NMR studies of charge ordering in organic conductors

Experimental evidences of the charge ordering with the use of 13 C -NMR techniques in various organic conductors are reviewed. In the insulating states of two-dimensional BEDT-TTF salts, α-I 3 and θ-RbZn(SCN) 4, the formation of charge stripes perpendicular to molecular stacks are confirmed. Charge disproportionation is estimated as 0.8:0.2 in the latter and more in the former. New type of charge ordering in a TTM-TTP salt with one-dimensional half-filled band is suggested.

Charge ordering in the one dimensional half-filled band system, (TTM-TTP)I 3}

13 C-NMR measurements have been carried out to investigate the nature of the electronic properties of the one-dimensional half-filled band system, (TTM-TTP)I 3 . It is known that this compound is metallic down to 160K. The metal-insulator transition into a non-magnetic ground state was confirmed from the temperature dependence of NMR relaxation rate. In addition, it was found that 13 C-NMR spectra split into two in the insulating state. This is a evidence of charge disproportionation among the organic molecules. It may be considered as a typical CDW formation in a 1D half-filled system with large intersite Coulomb repulsion.

Electronic state of a new organic conductor (TTM-TTP)I 3 with a one-dimensional half-filled band

13C NMR measurements have been carried out to investigate the nature of the electronic state of the one-dimensional half-filled band system, (TTM-TTP)I 3. Metal–insulator transition at around 120 K was observed through the temperature dependence of NMR relaxation rate, 1/ T 1. From the analysis of NMR spectra in the insulating state, it is strongly suggested that charge disproportionation with the valences of the TTM-TTP molecules 2-0-2-0 exists along the stacking axis.

Low Temperature X-Ray and ESR study of one-dimensional compound (TTM-TTP)I 3

(TTM-TTP)I 3 which has been considered as the typical one-dimensional half-filled band system, has been critically restudied by structural and magnetic measurements. X-ray diffuse scattering study reveals the formation of 2 k F CDW superstructure with the wave vector q 1=(0, 0, 0.5) below 160 K of the metal-insulator transition temperature. Another structural modulation with q 2= (0.5, 0, 0.5) is observed below 90–100 K. Modulated structure analysis using the q 2 satellite reflections and the Bragg reflections shows the large displacement in I 3 anion. Anomalies in χ, line width and g-value of ESR measurements which correspond to the structural anomaly, are also reported.

TTM-TTP-based metallic conductor with a half-filled band

A 1:1 composition organic conductor (TTM-TTP)I 3 has a highly one-dimensional half-filled band, but shows a metallic conductivity down to 160 K. Another 1:1 composition organic conductor (TTM-TTP)[C(CN) 3]has been prepared. This compound has a one-dimensional column similar to the I 3 − salt, but the packing pattern of the columns is different. This compound exhibits a metallic conductivity down to 70 K, an even lower temperature.

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.

Metallic ferromagnetism in a single-band model. III. One-dimensional half-filled band.

A single-band model recently proposed to describe metallic ferromagnetism is studied in a one-dimensional geometry in the half-filled-band case. The model describes a tight-binding band with on-site repulsion U and nearest-neighbor Coulomb exchange matrix element J. We determine the parameter regimes that give rise to partial and full spin polarization using exact diagonalization and analytic techniques. Ferromagnetism only occurs for J\ensuremath{\ne}0, with the required value of J decreasing as U increases and approaching zero as U\ensuremath{\rightarrow}\ensuremath{\infty}. A regime of partial spin polarization is found to exist for U less than the bandwidth. We examine the validity of mean-field theory for this model and find it to be remarkably effective in describing its physical properties.

Bond alternation in the infinite polyene: Effect of long-range Coulomb interactions

We investigate the effects of long-range Coulomb interactions on bond and site dimerizations in a one-dimensional half-filled band. It is shown that the ground state broken symmetry is determined by two sharp inequalities involving the Coulomb parameters. Broken symmetry with periodicity 2 k F is guaranteed only if the first inequality (downward convexity of the intersite potential) is obeyed, while the second inequality gives the phase boundary between the bond-dimerized and site-dimerized phases. Application of these inequalities to the Pariser-Parr-Pople model for linear polyenes shows that the infinite polyene has enhanced bond alternation for both Ohno and Mataga-Nishimoto parameterizations of the intersite Coulomb terms. The possible role of distant neighbour interactions in photogeneration experiments is discussed.

Broken symmetries in a one-dimensional half-filled band with arbitrarily long-range Coulomb interactions.

Resultat nouveau sur les symetries brisees dans une bande a moitie remplie unidimensionnelle avec interaction coulombienne

Soliton excitations in a commensurability 2 mixed peierls system

We consider a one-dimensional half-filled band system with the electrons coupled to both internal mode and bond modulation. For weak and intermediate coupling strength the site dimerization are mutually exclusive in the uniform ground states and inside neutral solitons. They coexist however inside charged solitons. The solitons carry charge ± e 2 per spin. Creation energy decreases as the two couplings become less different. The position of the gap state depends on the occupation number.

Effects of spin-orbit coupling on charge- and spin-density waves

The Hartree-Fock treatment of charge- and spin-density waves is extended to include a weak spin-orbit coupling for a one-dimensional half-filled band. It is found that charge and spin channels do not mix to any order of perturbation while each of them is affected to second order. A group theory argument is given, which shows that the absence of mixing should be peculiar to commensurability 2.