Quasi One-dimensional Systems Research Articles

Interchain conductivity of coupled Luttinger liquids and organic conductors

We reconsider the theory of dc and ac interchain conductivity in quasi-one dimensional systems. Our results are in good agreement with the measured c-axis optical conductivity of ${(\mathrm{TMTSF})}_{2}{\mathrm{ClO}}_{4}$ and suggest that the c-axis dc conductivity of ${(\mathrm{TMTSF})}_{2}{\mathrm{PF}}_{6}$ in the $150 \mathrm{K}<T<300 \mathrm{K}$ range is dominated by precursor effects of Mott localization. The crossover from a Luttinger liquid at high energy to a Fermi liquid at low energy is also addressed, within a dynamical mean-field theory. Implications for the interchain resistivity and Drude weight in the Fermi liquid regime are discussed.

Optical properties of low-dimensional systems : The Bechgaard salts case

We review our optical investigations on the organic Bechgaard salts. These prototype quasi-one dimensional systems reveal non-Fermi liquid features in their electrodynamic response. We show that various aspects of the exotic normal state properties along the chains are consistent with the predictions of the Tomonaga- Luttinger liquid theory or Luther-Emery model for one-dimensional systems. The role played by the interchain coupling will be also addressed.

Off-Diagonal Disorder in the Anderson Model of Localization

We examine the localization properties of the Anderson Hamiltonian with additional off-diagonal disorder using the transfer-matrix method and finite-size scaling. We compute the localization lengths and study the metal-insulator transition (MIT) as a function of diagonal disorder, as well as its energy dependence. Furthermore we investigate the different influence of odd and even system sizes on the localization properties in quasi one-dimensional systems. Applying the finite-size scaling approach in conjunction with a nonlinear fitting procedure yields the critical parameters of the MIT. In three dimensions, we find that the resulting critical exponent of the localization length agrees with the exponent for the Anderson model with pure diagonal disorder.

Low frequency dielectric spectroscopy of the Peierls-Mott insulating state in the deuterated copper-DCNQI systems

Combined optical and photoemission experiments on the quasi-one dimensional Bechgaard salts reveal the non-Fermi liquid character of these prototype quasi-one dimensional interacting electron systems. We show that various aspects of the exotic normal state properties along the chains are consistent with the predictions of the Tomonaga-Luttinger liquid theory. We also discuss the effect of interchain coupling on the insulator-metal transition, associated with the electron confinement-deconfinement crossover.

A Microscopic Description of Quantum Fluids Adsorbed in Carbon Nanotubes

Apart form their possible technological applications, the adsorption of quantum liquids inside carbon nanotubes allows for an experimental realization of quasi-one dimensional systems. We present a comparison between energetic and structural properties of 4 He and H 2 inside a (5,5) nanotube and in a pure 1D arrangement based in diffusion Monte Carlo calculations.

Spatial Correlations in the Valence of Metal Ions in Ni1-xPdx(chxn)2Br3

X-ray scattering experiments have been performed on a quasi-one dimensional system, Ni 1- x Pd x (chxn) 2 Br 3 . Strong diffuse scattering was observed for x > 0.7, and it was interpreted as due to spatial inhomogeneity in the valence of metal ions. This inhomogeneity takes the form of CDW in which the metal ions within a chain have valences alternating between +2 and +4. Correlations in the valence sequence could be determined parallel as well as perpendicular to the chain direction. Pair correlation functions deduced from the measurements show the existence of strong correlation between the positions of bridging Br ions and those of Br counter ions. It is concluded that the valence of metal ions for x <0.7 is +3. These results are consistent with previous data on optical and magnetic measurements.

Unconventional spin density waves in quasi-one dimensional systems

We consider the possibility of formation of an unconventional spin density wave (SDW) in quasi-one dimensional electronic systems. In analogy with unconventional superconductivity, we develop a mean field theory of SDW allowing for the momentum dependent gap A(k) on the Fermi surface. The excitation spectrum and basic thermodynamic properties of the model are found to be very similar to those of d-wave superconductors in spite of the different topology of their Fermi surfaces. Among the transport properties the frequency dependent conductivity in directions perpendicular to the linear chain direction is evaluated for various gap functions, and found to reflect the maximum gap value.

Cyclotron resonance in low-dimensional molecular metals

Abstract We examine cyclotron resonance (CR) behavior in low-dimensional molecular metals. Using a semiclassical model, we show how the conductivity in the least dispersive directions can dominate the CR response, and how this response is highly sensitive to the Fermi surface topology in both quasi two and quasi one-dimensional systems. We also discuss recent experimental progress.

Electronic Structure of Quasi-One Dimensional Models

Ladder models are studied as quasi-one dimensional tight binding systems. A set of iteration formula is derived for calculating local densities of states for various ladders including periodic, quasiperiodic and disordered ones. Band structures are analyzed.

SELF-MATCHING PROPERTY OF CORRELATED ELECTRONS: CHARGE–DENSITY WAVE ENHANCES SPIN ORDERING

Abstract The local minima of the free energy of a quasi one-dimensional electron system with short-range repulsion on a lattice were found which correspond with the symmetry allowed matching pairs of the precursor CDW and SDW modulation periods. Possible relation of the theory to the `staircase' instabilities in the doped nickelates with perovskite structure is discussed.

Effective electron Hamiltonian for a quasi one-dimensional system. The (TMTSF) X and the (TMTTF) X systems

In this paper we have introduced a variational approach to investigate the ground state of a model which includes both the Holstein electron-phonon interaction and the extended Hubbard electron-electron interaction. We have considered a variational state for the phonon subsystem which generalizes the previous used forms. This state allows to take into account the possibility of extended phonon mediated correlations. The effective electron Hamiltonian, which we have obtained, includes first and second neighbor electron-electron interaction terms. We have treated exactly, through a Lanczos method, this effective model in the one-dimensional case. We have applied our method to two Bechgaard salts and in these cases we have estimated the correlation parameters. We have shown that the introduction of electron-phonon interaction allows an estimate of the on site U and nearest-neighbor V Coulomb repulsion, which are in agreement with the experimental optical spectra of the above mentioned two compounds.

Velocity fluctuations of a column of water streaming down a wire: the possibility of one-dimensional turbulence

The results of measurements of the velocity fluctuations of a thin column of water streaming down a wire show that the dynamics of this process is turbulent at high injection flux and is characterized by a Kolmogorov like spectrum for the energy density. This density E(k), proportional to the power spectrum of the longitudinal velocity, scales as with reminiscent of Kolmogorov turbulence in three-dimensions. It is suggested that this system can be modeled as a quasi one-dimensional compressible system where the compressibility stems from the instability of the column to thickness fluctuations.

Optical conductivity of the Bechgaard salts: the sum rules revisited

The validity of the optical sum rules has been addressed eversince and was always matter of debate. Particularly controversial is the proof that the partial sum rules can be extended to both optical conductivity and energy loss function. We show in this paper that for both transverse (optical conductivity) and longitudinal (energy loss function) absorption processes the corresponding sum rule can be theoretically established and through appropriate conditions for the integration limits exactly verified. We also focus our attention on the one-dimensional case within the microscopic Hubbard model. An application of these concepts to the quasi one-dimensional systems, for which we have chosen the organic (TMTSF)2PF6 material, will also be presented.

Ac conductance of a quantum wire with electron-electron interactions

The complex ac-response of a quasi-one dimensional electron system in the one-band approximation with an interaction potential of finite range is investigated. It is shown that linear response is exact for this model. The influence of the screening of the electric field is discussed. The complex absorptive conductance is analyzed in terms of resistive, capacitive and inductive behaviors.

Imaging of a suspended helium film with 2-D electrons by interferometry

A helium film suspended between elevations on a substrate forms an excellent surface for a two-dimensional electron gas. With the structure on the substrate a quasi one-dimensional electron system can be created. Experiments probing the electrical transport properties of this system have raised questions about the suspended helium film itself. We report measurements of the suspended film using interferometry. The profile is mapped out as a function of the bulk helium level beneath the substrate. By measuring the electron signal simultaneously the relation between the signal and the film profile can be obtained.

Magnetic properties of the superconducting and nonsuperconducting spin ladders (Sr,Ca) 14Cu 24O 41

Abstract Magnetic measurements have been performed on the S = ½ quasi-one dimensional system of (Sr,Ca) 14 Cu 24 O 41 , which has both simple chains and two-legged ladders of copper ions. The total susceptibility of studied compounds has been shown to be anisotropic with anisotropy coming mainly from the Curie-Weiss term. The chains have a spin gap in the excitation spectrum, which originates from a dimerized state. Substantial doping of the system leads to superconductivity with a high critical temperature.

Growth of NMR multiple-quantum coherences in quasi-one-dimensional systems

Abstract It is shown that the second moment of the MQ-NMR intensities distribution is a convenient parameter for the quantitative description of the growth of MQ coherences. With the exact solution for the xx -model Hamiltonian the dependence of this second moment upon the preparation time in the MQ sequence is explicitly related to the structure of the sample. Calculations for a quasi-one dimensional system of uniformly-spaced spins forming a linear chain that take into account both intra- and interchain interactions are compared to experimental data.

Evolution of wave packets in quasi-one-dimensional and one-dimensional random media: Diffusion versus localization

We study numerically the evolution of wavepackets in quasi one-dimensional random systems described by a tight-binding Hamiltonian with long-range random interactions. Results are presented for the scaling properties of the width of packets in three time regimes: ballistic, diffusive and localized. Particular attention is given to the fluctuations of packet widths in both the diffusive and localized regime. Scaling properties of the steady-state distribution are also analyzed and compared with theoretical expression borrowed from one-dimensional Anderson theory. Analogies and differences with the kicked rotator model and the one-dimensional localization are discussed.

Quasi-one dimensional Hubbard system in Langmuir-Blodgett films of TCNQ complexes

In-situ ESR measurements have been performed on Langmuir-Blodgett films of several complexes of azobenzene-containing alkyl-chain-substituted pyridinium and TCNQ, which exhibit conductivity change upon the trans-cis photoisomerization of the azobenzene group. The quantitative analyses have allowed us to propose a conductivity-change mechanism, since these films can be treated as a quasi-one dimensional Hubbard system.

Characteristic SDW and FISDW behavior in (DMET-TSeF) 2X system

Abstract The quasi one-dimensional system (DMET-TSeF)2X which is similar to (TMTSF)2X is studied. The remarkable magnetic and transport properties for the salts with X=AuI2, AuBr2 and AuCl2 are shown. It is shown from the magnetic measurement that the AuBr2 salt becomes SDW at ambient pressure and its easy-axis is along the most conducting a-axis. FISDW states has been observed for X=AuCl2, AuI2 at ambient pressure and X=AuBr2 under pressure respectively. Low temperature structural analyses have confirmed no superstructure to exist for the AuI2 and AuCl2 salts. Hall effect measurements have revealed the sign change of the Hall voltage(AuI2) and the plateau-like Hall voltage(AuCl2), but at the higher fields than those reported for TMTSF system.