Conduction anisotropy and Hall effect in the organic conductor (TMTTF)2AsF6: Evidence for Luttinger liquid behavior and charge ordering (original) (raw)
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Hall effect in the normal phase of the organic conductors: (TMTSF) 2 ReO 4 vs. (TMTTF) 2 AsF 6
Journal de Physique IV (Proceedings), 2004
We report Hall effect measurements performed in the normal phase and at ambient pressure of (TMTSF) 2 ReO 4 and (more anisotropic) (TMTTF) 2 AsF 6 quasi-1D organic conductors. For T>200 K, the Hall coefficient of (TMTSF) 2 ReO 4 is smoothly temperature-dependent, and its value corresponds to a carrier concentration of one hole/unit cell. On the other hand, the Hall coefficient of (TMTTF) 2 AsF 6 is enhanced above 220 K, and the corresponding carrier concentration is almost 100 times lower than the expected one for one hole/unit cell. Our results give evidence for the existence of a high temperature regime above 200 K in (TMTTF) 2 X salts, where the 1D Luttinger liquid features appear in the transport properties.
The European Physical Journal B, 2001
We report a detailed characterization of quantum Hall effect (QHE) influence on the linear and non-linear resistivity tensor in FISDW phases of the organic conductor (TMTSF)2PF6. We show that the behavior at low electric fields, observed for nominally pure single-crystals with different values of the resistivity ratio, is fully consistent with a theoretical model, which takes QHE nature of FISDW and residual quasi-particle density associated with different crystal imperfection levels into account. The non-linearity in longitudinal and diagonal resistivity tensor components observed at large electric fields reconciles preceding contradictory results. Our theoretical model offers a qualitatively good explanation of the observed features if a sliding of the density wave with the concomitant destruction of QHE, switched on above a finite electric field, is taken into account.
Mid-infrared response of charge-ordered quasi-1D organic conductors (TMTTF) 2 X
Journal de Physique IV (Proceedings), 2005
We investigated the temperature dependence of the charge disproportionation in the charge ordered quasi one-dimensional conductors (TMTTF) 2 AsF 6 and (TMTTF) 2 PF 6 by infrared spectroscopy. In the mid-infrared, we observed a splitting of characteristic vibronic modes below the charge-order transition which can be directly linked to the charge disproportionation on the molecules. From our analysis of these modes we extracted the temperature dependence of the charge disproportionation which is much stronger in (TMTTF) 2 AsF 6 compared to (TMTTF) 2 PF 6. The charge disproportionation is only weakly affected by the spin-Peierls transition in the AsF 6 salts and remains basically unchanged in the PF 6 salts. Therefore, our data confirm that the spin-Peierls and charge-ordered ground state coexist at low temperatures.
2005
We present a detailed study of the Nernst effect Nzx in (TMTSF)2PF6 as a function of temperature, magnetic field magnitude and direction and pressure. As previously reported there is a large resonant-like structure as the magnetic field is rotated through crystallographic directions, the Lebed Magic Angles. These Nernst effect resonances strongly suggest that the transport of the system is effectively "coherent" only in crystallographic planes along or close to the applied field direction. We also present analytical and numerical calculations of the conductivity and thermoelectric tensors for (TMTSF)2PF6, based on a Boltzmann transport model within the semi-classical approximation. The Boltzmann transport calculation fails to describe the experiment data. We suggest that the answer may lie in field induced decoupling of the strongly correlated chains.
Infrared studies of charge ordering in quasi one-dimensional organic conductors
2004
Interactions between charge, spin, or lattice degrees of freedom result in the extraordinary rich phase diagram of the quasi one-dimensional (TMTTF)_2X and (TMTSF)_2X charge-transfer salts with ground states like charge order, spin order, anion order, and superconductivity. The focus of this contribution is on the charge-order transition in (TMTTF)_2AsF6 and (TMTTF)_2PF6 which is related to charge disproportionation along the molecular stacks at moderate temperatures T_CO. We investigated this phase transition into a ferroelectric state by infrared spectroscopy. For the first time, the lattice dynamics was explored in the vicinity of T_CO. We observed a splitting of the electron-molecular-vibration coupled totally symmetric intramolecular a_g(ν_3) mode in the charge-ordered state. From this result a charge disproportionation on the TMTTF molecular stacks of about 2:1 in (TMTTF)_2AsF6 and 1.25:1 in (TMTTF)_2PF6 can be estimated. Below T_CO, we found in both compounds new absorption modes in the conductivity spectrum at very low frequencies ν < 100 cm-1.
2017
α-(BEDT-TTF)_2I_3 is a prominent example of charge ordering among organic conductors. In this work we explore the details of transport within the charge-ordered as well as semimetallic phase at ambient pressure. In the high-temperature semimetallic phase, the mobilities and concentrations of both electrons and holes conspire in such a way to create an almost temperature-independent conductivity as well as a low Hall effect. We explain these phenomena as a consequence of a predominantly inter-pocket scattering which equalizes mobilities of the two types of charge carriers. At low temperatures, within the insulating charge-ordered phase two channels of conduction can be discerned: a temperature-dependent activation which follows the mean-field behavior, and a nearest-neighbor hopping contribution. Together with negative magnetoresistance, the latter relies on the presence of disorder. The charge-ordered phase also features a prominent dielectric peak which bears a similarity to relaxo...
Hall effect in the organic conductor (TMTSF)2NO3
Solid State Communications, 1996
Hall effect measurements of the organic conductor (TMTSF),NO, at low temperatures (1.8 I T 17 K) and high magnetic fields (H 5 8.5 T), are reported. The large Hall coefficient R, indicates the semimetallic nature of the spin density wave (SDW) ground state, whereas its positive sign shows the dominance of the hole carriers. Both R, and resistivity increase with decreasing temperature, which suggests the possibility that the carrier concentration is reduced as the temperature is lowered. The field variation of Hall resistance R,, deviates from the linear dependence for T 5 4 K and H 2 3 T. This could be interpreted not only by the temperature induced change in the number of carriers or anisotropy of their mobilities, but also by the possibility that the SDW state might change with the applied magnetic field.
Low-frequency dielectric response in the quasi-one-dimensional organic conductor (TMTSF) 2PF 6
Curr Appl Phys, 2009
A unique and rare opportunity of revealing the nature of the spin-density-wave (SDW) fluctuation in the quasi-one-dimensional organic conductor (TMTSF) 2 PF 6 has been provided by our AC impedance measurements above the SDW transition temperature. A close resemblance of the low-frequency dielectric response in the range between 20 K and the temperature of maximum resistivity T max $ 80 K to that in the SDW ground state was revealed, with quite compatible exponents for their power law dependencies. The SDW fluctuation has thus been identified in the 2D Fermi liquid regime, which can be regarded as a precursor phase of the SDW ground state.
Arxiv preprint arXiv: …, 2011
We have measured the Hall effect on recently synthesized single crystals of quasi-one-dimensional organic conductor TTF-TCNQ, a well known charge transfer complex that has two kinds of conductive stacks: the donor (TTF) and the acceptor (TCNQ) chains. The measurements were performed in the temperature interval 30 K < T < 300 K and for several different magnetic field and current directions through the crystal. By applying the equivalent isotropic sample (EIS) approach, we have demonstrated the importance of the choice of optimal geometry for accurate Hall effect measurements. Our results show, contrary to past belief, that the Hall coefficient does not depend on the geometry of measurements and that the Hall coefficient value is around zero in high temperature region (T > 150 K), implying that there is no dominance of either TTF or TCNQ chain. At lower temperatures, our measurements clearly prove that all three phase transitions of TTF-TCNQ could be identified from Hall effect measurements.