Ordering phenomena in quasi-one-dimensional organic conductors

Abstract

Low-dimensional organic conductors could establish themselves as model systems for the investigation of the physics in reduced dimensions. In the metallic state of a one-dimensional solid, Fermi-liquid theory breaks down and spin and charge degrees of freedom become separated. But the metallic phase is not stable in one dimension: as the temperature is reduced, the electronic charge and spin tend to arrange themselves in an ordered fashion due to strong correlations. The competition of the different interactions is responsible for which broken-symmetry ground state is eventually realized in a specific compound and which drives the system towards an insulating state. Here we review the various ordering phenomena and how they can be identified by optic and magnetic measurements. While the final results might look very similar in the case of a charge density wave and a charge-ordered metal, for instance, the physical cause is completely different. When density waves form, a gap opens in the density of states at the Fermi energy due to nesting of the one-dimension Fermi surface sheets. When a one-dimensional metal becomes a charge-ordered Mott insulator, on the other hand, the short-range Coulomb repulsion localizes the charge on the lattice sites and even causes certain charge patterns. We try to point out the similarities and conceptional differences of these phenomena and give an example for each of them. Particular emphasis will be put on collective phenomena which are inherently present as soon as ordering breaks the symmetry of the system.

Thermodynamic anomaly above the superconducting critical temperature in the quasi-one-dimensional superconductorTa4Pd3Te16

“…Despite the fluctuating CDW order being along the b-direction chains it would not necessarily give a strong resistivity boost in this direction. The three-dimensional character of the fluctuations could plausibly induce an inter-chain resistivity bump as instantaneous regions of CDW attempt to order the charge on the neighboring chains, as seen in other q1D systems on approach to spin or charge density wave transitions [10,34,35].…”

Light-Induced Current Oscillations in the Charge-Ordered State of (TMTTF)2SbF6

“…A two-state model assumes that "hot electrons" are generated in the conduction band similar as in inorganic semiconductors. Mori and collaborators [54,55] successfully applied this approach to β -(BEDT-TTF) 3 (HSO 4 ) 2 and (TMET-TTP) 4 PF 6 . The electron system is assumed to be decoupled from the lattice; hence an effective electron temperature T e can be defined.…”

“…The charge-transfer salts (TMTTF) 2 X, where TMTTF stands for tetramethyltetrathiafulvalene and X for a monovalent anion, have been under scrutiny due to their quasi-one-dimensional electronic character and ordering phenomena in the spin and charge sectors [1][2][3][4]. During the last years several comprehensive investigations have been conducted on the optical [5][6][7][8][9] and transport properties [10], the lattice [11,12] and electronic structure [13][14][15] as well as on the magnetic properties [16][17][18][19][20][21].…”

“…Later, this was extended to other organic systems, such as K(TCNQ) [35], where the switching was also recorded optically, expressing a stripe structure of alternating insulating and metallic domains between the two contacts. In the two-dimensional organic salt θ-(BEDT-TTF) 2 CsZn(SCN) 4 [36] and its sister compounds [37] the charge order was melted by applying a current to the crystal [30]. To date, no concept or model could be established that can explain all these observations in organic salts.…”

Comprehensive transport study of anisotropy and ordering phenomena in quasi-one-dimensional(TMTTF)2Xsalts (X=Kohler1, Rose2, Dumm3 et al. 2011Phys. Rev. B

“…The competition of the different interactions upon the charge, spin and lattice degrees of freedom is responsible for which broken-symmetry ground state is eventually realized in a specific compound and which drives the system towards an insulating state. 3 The family of the Fabre and Bechgaard salts have been the focus of enormous efforts during the last three decades because small variations of the molecules or moderate pressure tune the systems from antiferromagnetic insulator to spin-Peierls state, spin-density-wave state and superconductor, from a charge localized semiconductor, charge order and ferroelectricity to a Luttinger and Fermi-liquid metal. [4][5][6][7][8] These compounds are charge transfer salts consisting of stacks of the planar organic molecules TMTTF (which stands for tetramethyltetrathiafulvalene) along the a-axis that are separated in cdirection by monovalent anions.…”