Quasi One-dimensional Systems Research Articles

Dynamics of Sele-Localized Charge-Carriers in Quasi 1-D Solids

Abstract A theoretical study of the properties of large polarons in quasi one-dimensional systems, including intrachain scattering by phonons, phonon emission and absorption processes.

The structures of the tetracyanoplatinates, a class of quasi-onedimensional systems

The structures of the tetracyanoplatinates, a class of quasi-onedimensional systems

Subgroups of the magnetic axial point groups

All subgroups of the magnetic axial point groups are derived, and the invariant ones are indicated. These subgroups can be used in the determination of the symmetry of the low-temperature phase in phase transitions of crystals that are highly anisotropic in one direction (the ferroelectric transition of the chain-type crystal SbSI at 295K is considered as an example) and of quasi one-dimensional systems (where the order of the principal rotational axis may be any integer).

Non-exponential nuclear magnetic relaxation by solitary-waves in K 2Pt(CN) 4Cl 0.303.2H 2O

Pulsed NMR technique is used to study the 195Pt nuclear spin relaxation in KCP (Cl) in the temperature range 44 ⩽ T ⩽ 112 K where solitary waves are expected to be the main excitations of this quasi one-dimensional system. A theoretical explanation of the strongly non-exponential magnetization recovery is presented based on hopping of solitons in connection with NMR relaxation.

Commensurate-Incommensurate Phase Transition in Quasi One-Dimensional Electron-Phonon System: Nearly Half-Filled Band

Commensurate-Incommensurate Phase Transition in Quasi One-Dimensional Electron-Phonon System: Nearly Half-Filled Band

Magnetic properties of TMCuC : Mn, a quantum chain with classical impurities

The magnetic susceptibility of the mixed quasi one-dimensional system (CH 3) 4 N Mn x Cu 1−x Cl 3 has been measured down to 0.32K for x ranging between 0 an 1. At 4.2 K, the susceptibility starts to increase with x up to x ≅ 0.1 and then decreases rapidly. The Néel température decreases from 1.24 K for x = 0 to 0.35 K for x = 0.22. The experimental data at small values of x are well explained by a theoretical model of S= 1 2 quantum chain with classical impurities.

Antiferromagnetic ordering in the ytterbium aluminum perovskite YbAlO 3

The antiferromagnetic ordering in YbAlO 3 at low temperatures has been studied. Susceptibility measurements are in agreement with certain features of a quasi one-dimensional Ising system. Neutron diffraction below 0.8 K suggests a structure of the type A x G y . The spontaneous magnetic moment at 100 mK compares well with the value from the ground state doublet and is in disagreement with Mössbauer results.

The structures of the tetracyanoplatinates, a class of quasi-onedimensional systems

Abstract A summary is given on the structures of the tetracyanoplatinates (with formal Pt oxidation number 2.0 – 2.49) with alkali, earth alkali and lanthanoid cations. The features common to the structures of the partially oxidized tetracyanoplatinates and the tetracyanoplatinates(II) are outlined. The role of the cations, anions and water molecules in determining the crystal structure is discussed. Special interest is laid on the great variation of the inchain Pt – Pt distance R from about 3.75 Å to 3.09 Å (for compounds with the formal Pt oxidation number of two) and further from 2.92 Å to 2.80 Å (for the partially oxidized compounds). Conditions for structures with small values of R are given. Small Pt – Pt distances R should hence be looked for in tetracyanoplatinates with cations of high polarizability, low water content and strongly polarizing anions.

Nordheim-Gorter like behavior and one carrier conduction in a quasi-one-dimensional system

We report the extension and observation of Nordheim-Gorter type scaling of the thermoelectric power with the d.c. conductivity for the system of quasi-one-dimensional (QOD) conductors, (TTF) 12(SeCN) 7, (TTF) 12(SCN) 7, (TTF) 3(Cl) 2 and (TTF) 7(I) 5. The consideration of additional scattering processes for one carrier transport leads to a thermopower which scales linearly with conductivity. Furthermore, such a TEP vs conductivity (or resistivity) analysis will identify single carrier (or bi-carrier) transport in other QOD systems as well.

Insulating spin glasses

The possibility of obtaining spin glasses by addition of impurities in an antiferromagnetic insulator is examined. Dipolar interactions are briefly considered but the attention is focussed on Heisenberg systems. Equivalence with the Edwards-Anderson model is derived in a theoretical case. Experimental realisations, such as quasi-one dimensional systems, and spinels, are reviewed. A weak concentration of non-magnetic impurities can give rise to a new state that we call “semi spin glass”, in which a ferromagnetic component coexists with a transverse, spin glass component. An important case is when the pure system has a high ground state degeneracy (cooperative paramagnet). Non-magnetic impurities or other forms of disorder can transform it into a spin glass.

Electron Spin Resonance of Highly Anisotroic Organic Systems

Abstract After a brief discussion concerning the chemical nature and structural organization, ESR results obtained on low and highly conducting quasi one-dimensional organic systems, are presented. Related to the knowledge of the molecular properties, invaluable informations about the properties of the linear chains may be obtained on single crystals from the susceptibility, the g tensor and the line shape: existence of magnetically inequivalent sites, respective contributions of the different magnetic species (for low conducting systems) or of the different chains (for highly conducting systems). In particular cases, the existence of weak intrachain coupling has been pointed out and even some order of magnitude for the ratio of intra- to interchain exchange have been reached.

Wigner crystal model for quasi one-dimensional systems based on TCNQ

The value of the electron transfer, ρ, from donors (Rb, NMP) to acceptors (TCNQ) is studied by calculating the electrostatic energy of the Rb-TCNQ and NMP-TCNQ crystals as a function of ρ and using the spin susceptibility data for the NMS-TCNQ crystal. It is shown that for the Rb-TCNQ crystal ρ = 1 and for the NMP-TCNQ crystal ρ = 1 8 . The Wigner crystal model for highly conductive TCNQ salts is discussed.

Dynamical correlation functions for linear spin chains

Dynamical spin correlation functions are calculated numerically for cyclic linear Heisenberg chains containing up to 10 spins with S = 1 2 and S = 1. We consider ferro- and antiferromagnets including single-site and exchange anisotropies. The results agree well with the neutron scattering cross sections on quasi one-dimensional systems.

On the AB initio crystal orbital method

A new computer realization of the LCAO Hartree—Fock crystal orbital method using contracted Gaussian orbitals is reported. All integrals over the atomic orbitals are calculated explicitly within a finite interaction range. No approximation with respect to exchange is used. The spin-unrestricted Hartree—Fock-type crystal orbital formalism has been programmed, too. Both programs are limited to quasi one-dimensional systems at present, provide nevertheless a useful tool for the theoretical investigation of the electronic structure of simple polymers and one-dimensional models of solids. Basic information on both programs is documented.

Cooper pair and electron-hole pair instabilities in a quasi-one dimensional system

We calculate for an almost half-filled tight-binding band, the mean field ground state energy differences between the charge-density-wave (CDW) and BCS paired states for a truncated model Hamiltonian with zero-range instantaneous electron-electron interactions. The CDW pairing is found to be always unstable vis-à-vis BCS for a static lattice distortion of wave vector Q = (2 k F , π, π).

Field-Induced Charge-Carrier Trapping in the Photoconduction of a Quasi One-Dimensional System: Phenanthrene-Pyromellitic Acid Dianhydride

A field-dependent charge-carrier trapping process has been observed in the photoconduction mechanism of phenanthrene-pyromellitic acid dianhydride. This effect can be observed at electric field strengths exceeding ${10}^{3}$ V/cm. A calculation on the basis of a hopping model shows that field-induced charge-carrier trapping occurs in a three-dimensional system at critical field strengths well above ${10}^{6}$ V/cm. In a one-dimensional model, however, the critical field strength can be as low as 1 V/cm.

Peierls transition in a quasi-one dimensional system

We study the thermodynamics of a noninteracting electron system with a half filled strongly anisotropic tight binding band in the mean field approximation. This system may exhibit a structural transition dimerizing along the high conductivity direction. The conditions for the instability to occur are given as a function of the degree of anisotropy. The relationship to the behavior of TCNQ salts is discussed.

An organic ‘metal’?

LITTLE1 has proposed a mechanism by which an electron–electron (e–e) interaction in certain organic polymers and macromolecules might result in a high superconducting transition temperature. This e–e mechanism requires a combination of two systems consisting of a conducting or semiconducting polymeric compound forming a spine, with highly polarisable side chains attached to the spine. According to Little, the addition of such side chains can increase the e–e attraction in the spine to the point where it becomes energetically favourable to enter the superconducting state. This e–e mechanism of superconductivity has led to lively discussions, primarily concerned with superconductivity in quasi one and two-dimensional systems2,3, and the magnitude of the e–e attraction4,5. It has been shown theoretically3 that, depending on, the nature of the interaction between the electrons, a quasi one-dimensional system may exist in different states: metallic, dielectric, antiferromagnetic and superconducting. It has also been shown experimentally that the organic charge transfer salt N-methyl-pehnazinium tetracyanoqui-nodimethan has ‘metallic’ properties at temperatures above 200 K with a continuous transition to a small-band-gap insulator below 200 K (ref. 6).

Some Results Concerning the Crossover Behavior of Quasi—Two-Dimensional and Quasi—One-Dimensional Systems

A magnetic system with intraplanar and interplanar interaction strengths $J$ and $\mathrm{RJ}$ is is treated. Rigorous relations are established concerning the first few derivatives with respect to $R$ of the susceptibility $\ensuremath{\chi}(R)$. Considering $\ensuremath{\chi}(R)={b}_{0}+{b}_{1}R+{b}_{2}{R}^{2}+\ensuremath{\cdots}$, we find ${b}_{1}$ and the order of magnitude of ${b}_{2}$. Hence we can predict when the system crosses over from $d$-dimensional to $d$-dimensional behavior (e.g., for quasi---two-dimensional systems, $d=2$, $\overline{d}=3$, while for quasi---one-dimensional systems, $d=1$, $\overline{d}=3$). These results also support scaling with respect to the anisotropy parameter $R$.