Quasi-one Dimensional Organic Conductor Research Articles

Charge-Order Phase Transition in the Quasi One-Dimensional Organic Conductor {hbox {(TMTTF)}}_2 {hbox {NO}}_3

Low-dimensional organic conductors show a rich phase diagram, which has, despite all efforts, still some unexplored regions. Charge ordered phases present in many compounds of the {hbox {(TMTTF)}}_2X family are typically studied with their unique electronic properties in mind. An influence on the spin arrangement is, however, not expected at first glance. Here, we report temperature and angle dependent electron spin resonance (ESR) measurements on the quasi one-dimensional organic conductor {hbox {(TMTTF)}}_2 {hbox {NO}}_3. We found that the {hbox {(TMTTF)}}_2 {hbox {NO}}_3 compound develops a peculiar anisotropy with a doubled periodicity (ab'-plane) of the ESR linewidth below about T_{text {CO}}= ({250pm 10})~hbox {K}. This behavior is similar to observations in the related compounds {hbox {(TMTTF)}}_2X (X = {hbox {PF}}_6, {hbox {SbF}}_6 and {hbox {AsF}}_6), where it has been attributed to relaxation processes of magnetically inequivalent sites in the charge-ordered state. For the structural analogous {hbox {(TMTTF)}}_2 {hbox {ClO}}_4, known for the absence of charge order, such angular dependence of the ESR signal is not observed. Therefore, our ESR measurements lead us to conclude that a charge-order phase is stabilized in the title compound below T_{text {CO}} approx 250~hbox {K}.

Topological phase transition in quasi-one dimensional organic conductors.

We explore topological phase transition, which involves the energy spectra of field-induced spin-density-wave (FISDW) states in quasi-one dimensional (Q1D) organic conductors, using an extended Su-Schrieffer-Heeger (SSH) model. We show that, in presence of half magnetic-flux FISDW state, the system exhibits topologically nontrivial phases, which can be characterized by a nonzero Chern number. The nontrivial evolution of the bulk bands with chemical potential in a topological phase transition is discussed. We show that the system can have a similar phase diagram which is discussed in the Haldane’s model. We suggest that the topological feature should be tested experimentally in this organic system. These studies enrich the theoretical research on topologically nontrivial phases in the Q1D lattice system as compared to the Haldane topological phase appearing in the two-dimensional lattices.

Critical dynamics and domain motion from permittivity of the electronic ferroelectric (TMTTF)2AsF6

The quasi one-dimensional organic conductor (TMTTF)2AsF6 shows the charge ordering transition at TCO=101K to a state of the ferroelectric Mott insulator which is still well conducting. We present and interpret the experimental data on the gigantic dielectric response in the vicinity of TCO, concentrating on the frequency dependence of the inverse 1/ε of the complex permittivity ε=ε′+iε′′. Surprisingly for a ferroelectric, we could closely approach the 2nd order phase transition and to deeply reach the critical dynamics of the polarization. We could analyze the critical slowing-down when approaching TCO from both sides and to extract the anomalous power law for the frequency dependence of the order parameter viscosity. Moreover, below TCO we could extract a sharp absorption feature coming from a motion of domain walls which shows up at a frequency well below the relaxation rate.

Hofstadter butterflies and quantized Hall conductance in quasi-one dimensional organic conductors

We explore the structure of the energy spectra of quasi-one dimensional organic conductors subjected to the field-induced spin-density-wave (FISDW) state. We show that the structure of the energy spectra can exhibit Hofstadter butterfly, which is generally believed to appear in two dimensional systems. The phenomenon of the quantized Hall conductance due to FISDW is also investigated. We find that the Hall number L, which is defined by L = σxy/(e2/h), coincides with the number described by FISDW order parameter. The sign reversal of the quantized Hall conductance is discussed theoretically.

Re-entrant magnetic-field–induced charge and spin gaps in the coupled dual-chain quasi–one-dimensional organic conductor perylene2[Pt(mnt)2

An inductive method is used to follow the magnetic-field–dependent susceptibility of the coupled charge density wave (CDW) and spin-Peierls (SP) ordered state behavior in the dual-chain organic conductor perylene2[Pt(mnt)2]. In addition to the coexisting SP-CDW state phase below 8 K and 20 T, the measurements show that a second spin-gapped phase appears above 20 T that coincides with a field-induced insulating phase. The results support a strong coupling of the CDW and SP order parameters even in high magnetic fields, and provide new insight into the nature of the magnetic susceptibility of dual-chain spin and charge systems.

Magnetic and Electric Properties of Organic Conductors Probed by 13C-NMR Using Selective-Site Substituted Molecules

Quasi-One and quasi-two dimensional organic conductors consisting of TTF derivatives such as BEDT-TTF (bis-(ethylene-dithio)-tetra-thia-fulvalene) and TMTCF (C = S; TMTTF: tetra-methyl-tetra-thia-fulvalene, C = Se; TMTSF: tetra-methyl-tetra-selena-fulvalene) have been well investigated in condensed matter physics because of interest in the emerging electric and magnetic properties, such as the spin density wave, charge order, superconductivity, anti-ferromagnetism, and so on. To probe the electronic state, nuclear magnetic resonance (NMR) is one of the most powerful tools as the microscopic magnetometer. A number of 13C-NMR studies have been performed of the double-site central 13C=13C bond substituted molecules. However, problems with the coupled spin system of 13C=13C complicated the interpretation for observations on NMR. Therefore, single-site 13C-enriched molecules are desired. We summarize the problem of Pake doublet and the preparation of the single-site 13C-susbstituted BEDT-TTF and TMTCF molecules. We also demonstrate the superiority of 13C-NMR of the single-site 13C-susbstituted molecule utilizing the hyperfine coupling tensor.

77Se-NMR study of quasi-one dimensional organic conductor (TMTSF)2X

Quasi-one dimensional organic conductor (TMTSF)2X with octahedral anions X = PF6, AsF6, and SbF6 have been studied by NMR measurements at the Se-sites which are substantially responsible for conductivity in this system. Close resemblances in the temperature dependence of the spin-lattice relaxation rate 1/T1 and the evolution of internal field in the SDW state were observed in the three measured compounds. The existence of the sub-phases in the SDW phase of all these compounds, which is evidenced by T1 but not from spectrum measurements, indicates that this is a common feature among (TMTSF)2X system with an incommensurate SDW wave number and is associated with dynamic property rather than static one.

Phase diagram of the field-induced spin density wave state in [formula omitted] deduced from the specific heat measurements

We have measured the specific heat of the quasi-one dimensional organic conductor ( TMTSF ) 2 ClO 4 . The clear phase diagram of the field-induced spin density wave state was obtained from the density plot of the specific heat. We observed the reentrance to the metallic state and the tetracritical behavior quite clearly, though there is no evidence of the ”tree-like” structure.

Inhomogeneous superconductivity in quasi-one dimensional organic conductors and ropes of carbon nanotubes

Abstract It has been reported that, in quasi-one dimensional organic conductors, superconductivity may coexist macroscopically with non-superconducting states giving rise to an inhomogeneous phase. We investigate, based on the time-dependent Ginzburg–Landau theory, the effect of disorder on the stability of the superconducting phase in such a mixed state. We also focus on the interplay between superconductivity and disorder in ropes of carbon nanotubes. We show that the superconducting transition temperature in quasi-one organic conductors is reduced by disorder but does not obey the Abrikosov–Gorkov law. However, and contrary to what is expected, disorder can further superconductivity in ropes of carbon nanotubes.

Hall Effect in Quasi One-Dimensional Organic Conductors

We study the Hall effect in a system of weakly coupled Luttinger Liquid chains, using a Memory function approach to compute the Hall constant in the presence of umklapp scattering along the chains. In this approximation, the Hall constant decomposes into two terms: a high-frequency term and a Memory function term. For the case of zero umklapp scattering, where the Memory function vanishes, the Hall constant is simply the band value, in agreement with former results in a similar model with no dissipation along the chains. With umklapp scattering along the chains, we find a power-law temperature dependance of the Hall constant. We discuss the applications to quasi 1D organic conductors at high temperatures.

Role of the Dimerized Gap Due to Anion Ordering in the Quantized Hall Phases of Quasi-One Dimensional Organic Conductors

Role of the Dimerized Gap Due to Anion Ordering in the Quantized Hall Phases of Quasi-One Dimensional Organic Conductors

Effect of Electron Correlation on Angular Dependence of Magnetoconductivity

An effect of electron correlation is studied in an angular dependence of magnetoconductivity of quasi one-dimensional organic conductors. We investigate the effect of both quasi-particle’s lifetime and velocity due to the electron correlation near SDW in the magnetoconductivity. We found that the momentum dependence of lifetime strongly suppresses the one-dimensional axis magnetoconductivity at a magic angle θ=45°. On the other hand, the change of the momentum dependence of the velocity originating from the electron correlation enhances the interchain magnetoconductivity at θ=0°. These effects are explained from the momentum dependence of lifetime and velocity over the electron’s commensurate orbital on Fermi surface at the magic angles.

Spin susceptibility of one-dimensional extended Hubbard model at quarter filling

The ground-state property of one-dimensional extended Hubbard model is investigated at quarter filling. By using spin-charge factorized wave function in the U → ∞ limit, the effective exchange coupling J eff and spin susceptibility χ are calculated as a function of nearest-neighbor Coulomb interaction V. It is found that J eff is suppressed by the effect of V through charge fluctuation. The results indicate these quantities have no singularities at the transition point because of the Berezinskii–Kosterlitz–Thouless-type transition of charge ordering. We also confirm the results by exact diagonalization method in the realistic parameter range. The relevance to the experiments on quasi one-dimensional organic conductor ( DI-DCNQI ) 2 Ag is discussed.

Role of the dimerized gap due to anion ordering in the quantized hall phases of quasi-one dimensional organic conductors

Hall resistance and magnetic torque measurements have been carried out in the field-induced spin-density-wave (FISDW) phase of deuterated (TMTSF)2ClO4 for various cooling rates through the anion ordering temperature. We have found that the Hall resistance in the intermediate cooled state shows a phase transition from the non-quantized Hall phase to the quantized Hall phase (n=1) with hysteresis. We have also found that the magnetic torque in the non-quantized Hall phase rapidly decreases with increasing cooling rate. These results suggest that there is a new phase transition from the non-quantized Hall phase to the quantized Hall phase in (TMTSF)2ClO4.

Effect of the dimerized gap due to anion ordering in the field-induced spin-density-wave of quasi-one dimensional organic conductors

We have measured Hall resistance and magnetic torque in the field-induced spin-density-wave (FISDW) phase of deuterated (TMTSF) 2 ClO 4 for various cooling rates through the anion ordering temperature. The Hall resistance with the magnetic field parallel to c* is not sensitive to cooling rate above 16T. On the other hand, the Hall resistance between 9 and 14 T rapidly and continuously decreases with increasing cooling rate. This result means that the Hall resistance in the semimetallic SDW phase between 9 and 14 T is not quantized in the intermediate cooled states. A new phase transition from the non-quantized phase to the quantized (n = 1) Hall phase exists with hysteresis of the Hall resistance. Moreover, the new phase boundary is shifted towards a lower field when the cooling rate is increased. We have also found that the magnetic torque in the non-quantized phase rapidly decreases with increasing cooling rate. A possible ground state of non-quantized and Hall phase of the FISDW phase of (TMTSF) 2 ClO 4 is discussed from the viewpoint of the peculiar SDW nesting vector.

Hall effect in quasi one-dimensional organic conductors

We study the Hall effect in a system of weakly coupled Luttinger Liquid chains, using a Memory function approach to compute the Hall constant in the presence of umklapp scattering along the chains. In this approximation, the Hall constant decomposes into two terms: a high-frequency term and a Memory function term. For the case of zero umklapp scattering, where the Memory function vanishes, the Hall constant is simply the band value, in agreement with former results in a similar model with no dissipation along the chains. With umklapp scattering along the chains, we find a power-law temperature dependance of the Hall constant. We discuss the applications to quasi 1D organic conductors at high temperatures.

Uniaxial strain investigation on the metal-insulator transition of (EDO-TTF) 2PF 6

The quasi-one dimensional organic conductor (EDO-TTF) 2PF 6 shows the novel metal-insulator transition, which complies with the cooperative features of the tetramerization of EDO-TTF, the charge ordering of 0110 pattern, and the ordering of anion at ca. 280 K. In this paper, the effect of the uniaxial strain on the metal-insulator transition of (EDO-TTF) 2PF 6 was investigated by means of the transport measurement. In low pressure region, the transport behavior was differently modified depending on the direction of the compression. In the cases that the strain was applied along the b and a′ axes within the donor layer (intralayer), the transition temperature ( T MI) was slightly decreased or not changed and the jump of resistivity was suppressed with increasing the strain. Contrary, the T MI was enhanced remarkably to above 340 K by the strain along the interlayer direction. The present results indicate that the strain along the interlayer direction is more effective for stabilization of insulating phase than those along the interlayer directions. It has been reported that the intralayer direction is expanded while the interlayer distance is shortened below T MI because the anion slightly inserts into the donor layer by means of the low temperature X-ray measurement at ambient pressure. The enhancement of the metal-insulator transition by the uniaxial strain along the interlayer direction is consistent with this anisotropic distortion of the unit cell through the transition. With applying the large strain along each direction, the insulating phase was suppressed and the metallic phase appeared around the room temperature. The metal-insulator transition occurred below about 200 K with the feature of the second-order.

Quantum Capacitance Effects in Carbon Nanotube Field-Effect Devices

Carbon nanotube (CNT) based transistors, for example, are especially interesting for both fundamentals of quantum transport and technology. They are quasi one-dimensional organic conductors in which electrons can propagate ballistically over very long distances. A CNT can be used as a nanometric channel for a device in which electron transmission can be modulated by a suitable gate potential, just like in standard FET devices. In this work the coherent transport properties of a coaxially gated semiconducting CNT were calculated using an ab-initio approach based on a self-consistent density-functional tight-binding method and the non-equilibrium Green's function formalism we have previously implemented.

Functional and Highly Spatially Resolved ESR Imaging

Electron spin resonance imaging is a technique using similar principles to the established nuclear magnetic resonance imaging; however, the very fast electron-spin relaxation time constants of the former are an experimental challenge. In order to obtain T2-weighted as well as functional images spatially resolved in the micrometer range, we use temperature-dependent pulsed X-band ESR and the back-projection reconstruction method. We present here recent results of our imaging project focussing on quasi one-dimensional organic conductors, where even pulsed conduction electron-spin resonance is possible.

Non‐magnetic anion substitution in (TMTSF) 2 ClO 4 : consequences on superconductivity

The influence of non magnetic impurities on the superconductivity of the quasi-one dimensional organic conductor (TMTSF)2ClO4 is investigated. Non magnetic impurities are added through the substitution of up to 3% of the ClO4 anions by ReO4 anions. Transverse resistivity and magnetoresistance measurements were performed in the superconducting state down to 100 mK. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)