This article reviews the static and dynamic properties of spontaneous superstructures formed by electrons. Representations of such electronic crystals are charge density waves (CDW) and spin density waves in inorganic as well as organic low-dimensional materials. A special attention is paid to the collective effects in pinning and sliding of these superstructures, and the glassy properties at low temperature. Charge order and charge disproportionation which occur in organic materials resulting from correlation effects are analysed. Experiments under magnetic field, and more specifically field-induced CDWs are discussed. Properties of meso-and nanostructures of CDWs are also reviewed.

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Electronic crystals: an experimental overview

Superconductivity, that is, the possibility for electrons to flow through a conductor without any energy loss, has been the fuel for a very large number of industrial applications of physics in the twentieth century. Just to mention some of them which are important in current life, we have the power loss energy transfer, the production of very strong magnetic fields for medical imaging or for plasma confinement (the fusion problem) voltage standards, particle accelerators, and magnetic flux sensors.

Organic conductors: from charge density wave TTF-TCNQ to superconducting (TMTSF)2PF6.

We introduce the development of conductive organic molecular assemblies including organic metals, superconductors, single component conductors, conductive films, and conductive liquids, particularl...

Development of Conductive Organic Molecular Assemblies: Organic Metals, Superconductors, and Exotic Functional Materials

The authors have evaluated the temperature dependence of the tight-binding transfer integral between neighbouring cation molecules for some representative compounds of the (TMTSF)2X and (TMTTF)2X families using their recently determined low-temperature and/or high-pressure crystallographic structures. The changes in the transverse integrals in going from the new structures to the ambient temperature and pressure structures are largest for those integrals which show an antibonding character compared to the intrastack interaction. These changes lead to a low-temperature electronic picture which differs markedly from the well known high-temperature description. The transverse bonding and antibonding interactions tend to equalise for the atmospheric pressure supraconductor (TMTSF)2ClO4. The results suggest that the structure of the most metallic TMTTF salt, (TMTTF)2Br, is equivalent at a temperature T1 to the structure of (TMTSF)2X at T=T1 or (TMTTF)2PF6 at T=T1+300K with regard to the values of the transverse transfer integrals.

http://iopscience.iop.org/article/10.1088/0022-3719/19/20/016/pdf

Temperature dependence of the transfer integrals in the (TMTSF)2X and (TMTTF)2X families

Since the first discovery of an organic superconductor, TMTSF 2 PF 6 (TMTSF = tetramethyltetraselenafulvalene) with the superconducting transition temperature ( T c )=0.9 K under 12 kbar, by the su...

Materials viewpoint of organic superconductors

The structural and electrical properties of different (TMTTF) 2 MF 6 compounds are described and the role of the anion size is investigated through the behaviour of the SbF 6 salt for which a critical increase of the resistivity occurs below 154 K. The effects of alloying (TMTTF) 2 SbF 6 with AsF 6 or PF 6 is also studied and we show that this electrical anomaly still exists for small amount of doping. Finally the existence of structural instabilities involving centrosymmetrical anions is briefly discussed Etude des proprietes structurales et electriques de ces sels ou l'on etudie le role de la taille de l'anion, a partir du comportement du sel de SbF 6 pour lequel un accroissement critique de resistivite est observe a 154 K. Effet du dopage de (TMTTF) 2 SbF 6 par AsF 6 ou PF 6 : l'anomalie de resistivite persiste aux faibles taux de dopage. Discussion de l'existence d'instabilites structurales impliquant des anions centrosymetriques

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Structural and electrical properties of (TMTTF)2MF6 salts (M = P, As, Sb). Rôle of the anions

The neutron (1. =1.1750A) high pressure (7 102MPa) and low temperature (1.7K) structure of (TMTSF)2PF6 (Di(2,3,6,7-tetramethyl-1,4,5,8-tetraselenafulvalenium hexafluorophosphate; 2(C10H12Se4)1/2+, PF6 −, Mr=1041.06) is reported. The lattice is triclinic P and cell parameters: The geometry of the Tmtsf stacks changes little under constraint exception made for a shortening in the interplanar spacing. For the titled compound at 7 102 MPa a temperature decrease from 300K to 4K is equivalent to the effect of an extra 2 102MPa applied pressure. However temperature (rather than pressure) is responsible for a small change in the transverse shift of adjacent Tmtsf molecules in a same column. Similarly pressure has little effect on the PF6 − anion disorder at a given temperature. If the low temperature TMTSF packing of (TMTSF)2PF6 (superconducting below ≃ 1.2K and above 9.5 102 MPa) is compared to that of (Tmtsf)2 C104 (superconducting below ≃1,2K at ambient pressure), the intrachain interactions are found...

Low Temperature and High Pressure (1.7K & 7 102 MPa) Structure of the First Superconducting Organic Salt (TMTSF)2 PF6

At T ∼ 24K, the quasi one dimensional organic superconductor (TMTSF)2CϱO4 shows a structural transition leading to a doubling (a × 2b × c) of the unit cell. The neutron average structure (i.e. superlattice reflections not included) at T = 7K has already been published. In the present paper, we report the results of a rigid body refinement of the low temperature (T ∼ 10K) structure from both the earlier set of neutron main reflection intensities and an extra set of X-ray superlattice intensities. This improved structural description clearly shows that the anion orientations alternate in the b direction only and that there is no significant TMTSF displacement from the average position. We compare these results with recent structural data obtained on (TMTSF)2ReO4 which exhibits below T ∼ 180 K an insulating ground state instead of the metallic one for the perchlorate salt.

B. Gallois

Papers

Structural and electrical properties of (TMTTF)2MF6 salts (M = P, As, Sb). Rôle of the anions

Low Temperature and High Pressure (1.7K & 7 102 MPa) Structure of the First Superconducting Organic Salt (TMTSF)2 PF6

Structure of Di-Tetramethyltetraselen-afulvalenium Perchlorate (TMTSF)2 CϱO4 in its Low Temperature (T ∼ 10 K) Ordered Phase

Crystallographic structures of (TMTSF)2 PF6 under constraint: evidence of a change in the electronic structure

Competition between spin-peierls and antiferromagnetic instabilities for cation radical salts of the TTF family: A review of experimental results