Quasi One-dimensional Compounds Research Articles

Shape memory effect nanotools for nano-creation: examples of nanowire-based devices with charge density waves

Nanotweezers based on the shape memory effect have been developed and tested. In combination with a commercial nanomanipulator, they allow 3D nanoscale operation controlled in a scanning electron microscope. Here we apply the tweezers for the fabrication of nanostructures based on whiskers of NbS3, a quasi one-dimensional compound with room-temperature charge density wave (CDW). The nanowhiskers were separated without damage from the growth batch, an entangled array, and safely transferred to a substrate with a preliminary deposited Au film. The contacts were fabricated with Pt sputtering on top of the whisker and the film. The high degree of synchronization of the sliding CDW under a RF field with a frequency up to 600 MHz confirms the high quality of the contacts and of the sample structure after the manipulations. The proposed technique paves the way to novel type micro- and nanostructures fabrication and their various applications.

Magnetic Order in the Frustrated Ising Quasi-One Dimensional Compound NaCo(acac)3∙ Benzene

We report the results of susceptibility, magnetization curve, and specific heat measurements on single crystals of NaCo(acac)3 ∙ benzene, which forms a triangular lattice on the ab-plane with Ising ferromagnetic chains along the c-axis. We found a long-range order below 62 mK by specific heat measurement, a steplike increase in susceptibility at this temperature, and a plateau of one-third of the full moment in the M–H curve at 20 mK. We also observed a spin relaxation that obeys the Arrhenius law in the ordered state. The existence of a partially disordered antiferromagnetic state is discussed on the basis of the results.

Crystallographic Aspects of the CDW Instabilities in NbSe3

Charge-density waves (CDW) in some quasi one-dimensional compounds can be depinned from the lattice by an external electric field. In the case of NbSe3, two CDW transitions have been reported with onset temperatures of 144 K and 59 K. From an analysis of the published low-temperature (LT) scanning tunneling microscopy (STM) images, which inherently allow the resolution of domain structures on the atomic scale, an alternative model of the CDW modulated structures in NbSe3 is proposed. In contrast to the existing model, where two incommensurate (IC) modes, q1 = (0,0.241,0) and q2 = (0.5,0.260,0.5) are selectively confined to two of three available structurally distinguished types of bi-capped trigonal prismatic columns, the alternative model [1,2] proceeds from the assumption that both columns of the same pair are alternatively modulated by the two modes, whose IC components add within experimental error into a commensurate value. The observed domains are formed as a result of the different bonding within and between the structural layers, separated by Van der Waals gaps, and of the ability of the two modes to be easily interchanged between two symmetry-related columns of the same type. This assumption is in accord with the published LT STM results, which confirm i.a. the presence of both IC modes above 59 K, where according to the previous model only the q1 contribution should be expected. A pair of two alternatively modulated columns of the same type represents the basic structural unit of the CDW ground state. The two modes can formally be replaced by a single inharmonic modulation, obtained by "beating" between the two IC modes.

Magnetic states of the five-orbital Hubbard model for one-dimensional iron-based superconductors

The magnetic phase diagrams of models for quasi one-dimensional compounds belonging to the iron-based superconductors family are presented. The five-orbital Hubbard model and the real-space Hartree-Fock approximation are employed, supplemented by density functional theory to obtain the hopping amplitudes. Phase diagrams are constructed varying the Hubbard $U$ and Hund $J$ couplings and at zero temperature. The study is carried out at electronic density (electrons per iron) $n = 5.0$, which is of relevance for the already known material TlFeSe$_2$, and also at $n = 6.0$, where representative compounds still need to be synthesized. At $n = 5.0$ there is a clear dominance of staggered spin order along the chain direction. At $n = 6.0$ and the realistic Hund coupling $J/U = 0.25$, the phase diagram is far richer including a variety of ``block'' states involving ferromagnetic clusters that are antiferromagnetically coupled, in qualitative agreement with recent Density Matrix Renormalization Group calculations for the three-orbital Hubbard model in a different context. These block states arise from the competition between ferromagnetic order (induced by double exchange, and prevailing at large $J/U$) and antiferromagnetic order (dominating at small $J/U$). The density of states and orbital compositions of the many phases are also provided.

Charge-orbital-lattice coupling effects in theddexcitation profile of one-dimensional cuprates

We identify dd-excitations in the quasi-one dimensional compound Ca$_2$Y$_2$Cu$_5$O$_{10}$ using resonant inelastic x-ray scattering. By tuning across the Cu L$_3$-edge, we observe abrupt shifts in the dd-peak positions as a function of incident photon energy. This observation demonstrates orbital-specific coupling of the high-energy excited states of the system to the low-energy degrees of freedom. A Franck-Condon treatment of electron-lattice coupling, consistent with other measurements in this compound, reproduces these shifts, explains the Gaussian lineshapes, and highlights charge-orbital-lattice renormalization in the high energy d-manifold.

Tunable harmonic vibrations of quasi one-dimensional conductors induced by sliding charge-density waves

We demonstrate that samples of quasi one-dimensional compounds show torsional vibrations induced by the sliding charge-density wave (CDW). Narrowband noise at the fundamental frequency is found in the vibrations spectra. The result suggests an approach to studies of the CDW dynamics and presents CDW conductors as tunable (ultra)sonic acoustoelectronic generators---unique solids vibrating under dc voltage.

不規則性をもつ結晶，超イオン導電体，非晶質，ガラス，融体の構造解析―不規則系・ランダム系の結晶学―１．周期系における不規則性の解析 有機擬一次元物質の秩序無秩序転移と電荷不均一化

High resolution X-ray structure analyses revealed the condition for the charge ordering (CO) observed in the quasi one-dimensional compounds (TMTTF) 2X. The size and orientational ordering of the counter anion X control the dimerization and tetramerization of TMTTF molecules. The molecular dimerization suppresses the 4kF CO, while the tetramerization assists the 2kF CO. The phase diagram of the electronic states including 2kF and 4kF CO has been proposed associated with magnitudes of the molecular dimerization and tetramerization.

X-ray study of modulated structures of beta-Cu x V 2 O 5

High resolution X-ray study reveals the wave vector change in the modulated structure of the quasi-one dimensional compound beta'-Cu vanadium bronze. Structural modulation of the reduced wave vector q0 = (0, 0.305, 0) emerges below 220 K in beta'-Cu0.29V2O5 . For beta'-Cu0.39V2O5, not the single q modulation but two kinds of modulations were observed. A three-fold superlattice structure with q1 = (0, 0.333, 0) appears below 210 K. An incommensurate modulated structure with q2 = (0, 0.26 ? 0.29, 0) coexists below 175 K, whose satellite intensity and b* component Qb have temperature and passing-time dependencies between 140 K and 175 K. The competition between q1 and q2 modulations was also observed. It seems that the q2 is deeply related to the physical property change between 140 K and 180 K confirmed by the decrease in the magnetic susceptibility and the increase in the resistivity.

Infrared properties of W-doped charge-density-wave material K0.3MoO3

The optical conductivity spectra of quasi-one dimensional compounds K0.3Mo1−xWxO3 (x=0, 0.03 and 0.15) have been studied over broad frequencies. While the DC resistivity measurements indicate no sign of CDW transition in heavily W-doped blue bronze, the optical conductivity spectra still show a single particle gap at around 0.2eV for E parallel to the chain direction. Such impurity effect challenges our understanding about the occurrence of the optical gap with the CDW transition.

Possible AF Order in F-AF Random Alternating Heisenberg Chain

The S = ½ ferromagnetic (F) - antiferromagnetic (AF) random alternating Heisenberg quantum spin chain is investigated by the quantum Monte Carlo method. The randomness is only present on the strong bonds taking values of ′2J randomly, and the weak bonds are uniformly antiferromagnetic with J. The model corresponds to the quasi one-dimensional compound, (CH 3 ) 2 CHNH 3 Cu(Cl x , Br 1 - x ) 3 , whose ground state interpolates the Haldane state of the F-AF alternating spin chain at x = 1 and the singlet-dimer state of the AF-AF alternating spin chain at x = 0. The nonequilibrium relaxation function of the staggered magnetic susceptibility exhibits algebraic divergence in the intermediate region of 0.44 < x < 0.87, which explains the experimental observation of the magnetic phase transition. The results suggest that the antiferromagnetic order becomes critical by the randomness of the bond distributions even in the presence of the rich ferromagnetic bonds.

Tuning anisotropy by impurities: magnetocaloric experiments on CsNi 0.9 Fe 0.1 Cl 3

The magnetic phase diagram of the Fe2+ doped hexagonal ABX3 compound CsNi0.9Fe0.1Cl3 is investigated by heat capacity and magnetocaloric experiments. In spite of the high doping concentration, some phase boundaries appear surprisingly well-defined, while others are broadened significantly. The discussion of this behaviour clarifies the potentials and limitations of doping as a means to manipulate the effective anisotropy in quasi one-dimensional ABX3 compounds.

Decay Processes of a Photo-Excited State in a Strong Electron-Phonon Coupling System Trans-[Pt(en)2Cl2](ClO4)2

A quasi one-dimensional compound of halogen-bridged mixed-valence platinum complexes [Pt(en)2][Pt(en)2X2] (ClO4)4 (X=Cl, Br, and I, and en denotes ethylenediamine, hereafter we abbreviate as Pt–X) is known to show a strong charge-transfer (CT) absorption. By the optical excitation of the CT band, one can make a CT exciton on a one-dimensional chain. The CT exciton relaxes, without a barrier, to localized ed exciton (STE) states and the relaxation process was observed as a series of Raman lines followed by a large broad luminescence band. Recent spectroscopic measurement of femtosecond time resolved luminescence by Tomimoto et al. revealed a wave-packet oscillation in an adiabatic potential well associated with a self-trapped exciton. 3) The time constants of cooling from the photo-excited states to the STE states were identified as 0.21 and 0.43 ps for Pt–Cl and Pt–Br, respectively. Recently, optical spectra were measured at a He temperature on a crystal of trans-[Pt(en)2Cl2](ClO4)2 which consists of the same chemical composition as the Pt–Cl. The absorption band observed at the lowest energy of 3.3 eV was due to the d-d transition on a platinum atom. 5) The luminescence spectrum had a Gaussianlike lineshape formed by the superposition of phonon side bands more than 20 series. The energy of phonons observed in the luminescence was quite close to that of a breathing mode of chlorines centered around the platinum ion (44.9meV) observed on the Raman spectrum. On the other hand, no phonon structures were observed on the luminescence of both one-dimensional Pt– Cl and Pt–Br. The electron phonon coupling strength (Huang-Rhys factor) of trans-[Pt(en)2Cl2](ClO4)2 was obtained to be 9.52. These results show that trans[Pt(en)2Cl2](ClO4)2 is a strong electron-phonon coupling system and that one of most suitable materials for the studies of the dynamical decay processes of photo-excited states in a strong electron-phonon coupling system. Special interest is at the point of comparison with onedimensional Pt–X. In this report, time resolved luminescence spectra of trans-[Pt(en)2Cl2](ClO4)2 are for various temperatures and the photo-excited state is shown to be cool-down on the adiabatic potential surface of the excited state at about 1 ns. self-trapp

A Structural Study of the Quasi One-Dimensional Compound (Ca1−xYx)0.82CuO2 Prepared at Room Pressure

A solid solution of the quasi one-dimensional cuprate, (Ca1−xYx)0.82CuO2 (0≤x≤0.435), has been successfully synthesized in an oxygen stream at room pressure. Structural changes have been determined for the basic crystal structure by means of the Rietveld method using powder X-ray diffraction. Upon Y doping, the nearest (intrachain) Cu–Cu distance increases from 1.93 to 1.98 Å, while the next-nearest (interchain) Cu–Cu distance decreases from 3.46 to 3.41 Å. The incommensurate superstructure, originating from differences in the periodic arrangement of the (Ca,Y) atoms and CuO2 chains, has also been examined. The modulation period along the crystal a axis implies that the stoichiometry of the solid solution shifts toward that of the cation-deficient member (Ca1−xYx)0.80CuO2. This compositional discrepancy might be canceled by the large change in the modulation period along the c axis.

X-ray structural study of 4 kF Superlattice in (DIDCNQI) 2Ag

X-ray diffuse scattering study using monochromatic camera revealed c */2 satellite reflections indicating three dimensional 4 k F CDW formation in quasi one-dimensional compound (DIDCNQI) 2Ag below 200 K.

Transverse transport in organic conductors: possible evidence for a Luttinger liquid

We present c-axis resistivity measurements performed on the organic conductors and under pressure. The aim is to probe the density of states of quasi-one dimensional compounds the high temperature properties of which are those of a Luttinger liquid. It is found that the 1-D Luttinger description breaks down below a specific pressure-dependent temperature, giving rise to a transient regime. The Fermi liquid behaviour is however restored at low temperature i.e. around 10 K, as evidenced by NMR measurements. Accordingly, two different energy scales 100 K and 10 K are required to get a fair understanding of all observed physical phenomena. Our interpretation supports the picture of a power law exponent for the correlation functions of the order of 0.25–0.30.

Spectral functions of one-dimensional models of correlated electrons

Using the Ogata-Shiba wave function, the spectral functions of the one-dimensional infinite U Hubbard model are calculated for various concentrations. It is shown that the ``shadow band'' feature due to 2k_F fluctuations becomes more intense close to half-filling. Comparing these results with exact diagonalization data obtained on finite clusters for the finite U Hubbard model and for the t-J model, it is also shown that this feature remains well-defined for physically reasonable values of the parameters (U/t\simeq 10, J/t\simeq 0.4). The ``shadow'' structure in the spectral functions should thus be observable in angle-resolved photoemission experiments for a variety of quasi-one dimensional compounds.

Low-frequency transport and relaxation of charge density waves in (TaSe4)2I crystals

A charge density wave (CDW) occurs in low-dimensional solids as a consequence of the Peierls transition. Various field- and frequency-dependent effects, as well as those of excess noise, are related to CDW transport. We investigate low-frequency (10-10 6 Hz) dielectric relaxation as well as voltage fluctuations as a result of internal dynamic or sliding CDW in quasi one-dimensional chain compound (TaSe4)21 single crystals. The activation energy for normal conduction obtained from low field resistivity was ΔE = 0.122 ± 0.004eV. The most useful expression of dielectric relaxation for a strong damped system with one degree of freedom is e(ω) α(1 + iωτ 0 ) -1 , where relaxation times are distributed at the average τ 0 . τ 0 versus 1/T shows thermal activation ΔE = 0.124 ± 0.004eV. Voltage fluctuations produced by a sliding CDW are found to originate from random thermally activated transitions between metastable states. Noise power spectra between 500Hz and 600kHz at temperatures between 165 and 215K have S(f) α f -α dependence. The distribution of relaxation times and the temperature-dependent shortest relaxation time reflect CDW internal dynamics and the importance of free carriers on it.

Quantization of nonlinear conductance in quasi one-dimensional compound m-TaS3 near Peierls transition temperature

The dependences of differential conductance σd(VDC, T) on DC voltage VDC and temperature T were measured in Peierls conductor m-TaS3 in the presence of strong RF-field near Peierls transition temperature TP2=157.5 K. We observed that 1) the function σd(0,T) has a maximum at T0=146.8 K in addition to the usual one at T=TP2; 2) steps appear in the σd(VDC)-curve at T≥T0. The steps are periodic both in VDC and in σd. Temperature independent magnitude of the steps is [(54±8) kOhm]−1, i.e. 4 times less than the quantum of ballistic conductance 2e2/h.

Evidence of charge-density-wave fluctuations in the low frequency optical conductivity of K0.3MoO3and (TaSe4)2I

Abstract The low temperature charge-density-wave (CDW) ground state has been extensively studied in the model quasi one-dimensional compounds K0.3MoO3 (blue bronze) and (TaSe4)2I. Below the Peierls transition temperature T 3D (183 K and 263 K in blue bronze and (TaSe4)2I, respectively) the conduction electrons exhibit long-range, three-dimensional order, and the interesting low temperature properties, including the pinned mode resonance and bound phonon states, have been clearly established. In contrast, the high temperature metallic state in these compounds has not been characterized nearly as extensively. In this paper we present the results of optical conductivity measurements performed above T 3D in the millimeter and submillimeter frequency range which, when combined with higher frequency infrared to ultraviolet reflectivity measurements, show clear deviations from simple metallic behavior. Futhermore, the pronounced excitations which appear in the spectra below 50 cm−1 for the electric field E polar...

TaTe4]4[PtI6]I2, ein neues quaternäres Tellurid-Iodid mit Kettenstruktur / [TaTe4]4[PtI6]I2, A New Quaternary Telluride-Iodide with Chain Structure

[TaTe4]4[PtI6]I2 was synthesized from the elements at 680°C. Its crystal structure was determined using single crystal methods. The structure of the quasi one-dimensional compound [TaTe4]4[PtI6]I2 (P1̄, Z = 1, a = 16.831(1), b = 17.740(1), c = 19.018(1)Å, α = 93.57°, β = 94.08°, γ = 102.09°) consists of Ta(Te2)2 chains separated by PtI6 groups and I atoms. The formal oxidation state assignment [(Ta5+)(Te2 2-)2]4[(Pt4+)(I-)6](I-)2 indicates that semiconducting properties are to be expected for this material.