Bruno Hilti

Conducting and superconducting salts based on BEDTTTF and on some unsymmetrical tetrachalcogenafulvalenes

Abstract The physical properties of conducting and superconducting salts based on bis(ethylenedithio) tetrathiafulvalene and on some unsymmetrical tetrathiafulvalenes (containing ethylenedithio-,ethylenedioxy-,vinylenedithio-,dimethylethylenedithio-, and pyrazino- as additional heterogroups) are reportd. β-, υ-, and τ-phases are found to be the most important.

Observation of the coherence peak of 1H-NMR relaxation rate in the superconducting state of (MDT-TTF)2Aul2

Abstract We have investigated the superconductivity in the organic conductor, (MDT-TTF)2Aul2 (Tc = 4.1 K) from the temperature dependence of 1H nuclear relaxation rate, 1 T 1 , measured by the field cycling method. The nuclear relaxation above 3 K is well characterized by a single relaxation time for nearly two decades. In the normal state, the standard Korringa relaxation holds. 1 T 1 just below Tc showed a clear enhancement, followed by a falling-off at lower temperatures. This behavior is just as predicted in the BCS theory (coherence peak) and implies that this material is a conventional superconductor with an isotropic gap. The decay of the nuclear magnetization below 3 K appeared non-sinle exponential. This is explained as the effect of trapped vortices.

Transparent electrically conductive composite materials: Methods of preparation and their application

One possibility to obtain transparent, electrically conductive materials is the crystallization of conducting charge-transfer-complexes (CT-complexes) in a polymer matrix in the form of needle-or dendrite-like structures. With tetraselenotetracene chloride ((TSeT)2Cl), a radical cation salt, as electroconductive filler, we have access to a thermally stable, highly conductive material, with values of the bulk conductivity of the composite material up to 1 S/cm at a loading of the conductive complex below 1 %(w/w). The preparation of such composite structures as free standing (cast) films and in the form of very thin coated layers is presented and their electrical, optical and mechanical properties are discussed. In addition we show their potential use for display electrodes, transparent heating elements, and for antistatic applications.

Conducting and Superconducting Salts Based on Some Symmetrical and Unsymmetrical Donors

Conducting and superconducting salts based on bis(ethylenedithio)tetrathiafulvalene, ehtylenedithioselenatrithiafulvalene, ethylenedioxyethylenedithiotetrathiafulvalene, and ethylenedioxyvinylenedithiotetrathiafulvalene were prepared and studied.

Physical properties in the normal state of the molecular superconductor κ-(BEDT)2Cu2(CN)3

Abstract We have investigated the electrical, spectroscopic and magnetic properties of the κ-phase molecular conductor κ -(BEDT) 2 Cu 2 (CN) 3 between room temperature and the liquid He 4 temperature range. We have shown that an intermittent superconducting materials is present around or below 4 K which presents above this temperature limited spin fluctuations. The influence of disorder inside the anionic layers is discussed with respect to the X-ray crystal structure, and also the intrinsic effects due to temperature or pressure to explain this situation. Finally, the specific behaviour of the ESR linewidth at low temperature is analysed as a magnetic precursor regime of the supposed superconducting ground state.

Synthesis, superconductivity and X-ray data of the complex of the non symmetrical 4,5-d4-4′,5′-h4-BEDT-TTF with copper rhodanide

Abstract The specific synthesis of the non symmetrical donor 4,5-d 4 -4′5′-h 4 -Bis-(ethylenedithio)-TTF (d 4 ,h 4 -BEDT-TTF) and some preliminary structural data and physical properties of its κ-complex with Cu(SCN) 2 are described.

Electrical conduction and electronic structures of novel tetrathionaphthalene derivatives

The electrical conduction of pristine (undoped) and iodine doped vacuum deposited films of the novel donors, dibenzodithiotetra‐thionaphthalene and dibenzodithiotetraselenonaphthalene were measured. The electronic structures of these donor compounds were examined experimentally by ultraviolet photoelectron spectroscopy and theoretically by semiempirical MO calculations and compared with the corresponding data of tetrathiotetracene.

Structures and conductivities of a series of new charge transfer salts with tetraselenotetracene (TSeT): TSeT(PF6)0.5, TSeT(AsF6)0.5, TSeT(PF6)0.4, TSeT(AsF6)0.43

Abstract The new charge transfer salts TSeT(PF6)0.5, TSeT(PF6)0.4, TSeT(AsF6)0.5 and TSeT(AsF6)0.43 have been prepared. Their crystal structures and semiconducting electrical conductivities are reported and discussed in the context of the search for superconducting materials analogous to TMTSeF(PF6)0.5.

Transparent electrically conductive composites by in situ crystallization of (TSeT)2Cl in a polymer matrix

A new chemical pathway was found which offers access to the thermostable, highly conductive tetraselenotetracene chloride radical cation salt (TSeT)2Cl. This pathway allows the in-situ crystallization of (TSeT)2Cl in a vitrifying polymer matrix. So highly conductive films (σ= 1–5 Scm-1) with networks of (TSeT)2Cl crystallites of a 1: 1000 aspect ratio could be prepared at a fairly low percolation threshold of 0.4 – 1.6 % w/w. These films show metallic conductivity behavior in the 60 – 400 K range.

Magnetic penetration depth of the k-phase family of organic superconductors

Abstract The magnetic penetration depth, λ, of a series of k -phase organic superconductors has been investigated by complex susceptibility measurements. It has been found that the so-called 10-K superconductors, k -(BEDT-TTF) 2 Cu(NCS) 2 and k -(BEDT-TTF) 2 Cu[N(CN) 2 ]Br, have similar characteristics: power-law temperature-dependence at low temperatures and macroscopic parallel penetration depth, λ (200μm). k -(BEDT-TTF) 2 Ag(CN) 2 H 2 O with T c of 5 K has a smaller value of λ (80μm). k -(MDT-TTF) 2 AuI 2 with T c of 4.3 K has a further smaller depth (less than 20μm). These results indicate that the interlayer superconducting coupling is strongly dependent on the compound among the k -phase family; superconductive dimensionality is the highest in k -(MDT-TTF) 2 AuI 2 but trends two-dimensional in k -(BEDT-TTF) 2 CuX [X=(NCS) 2 and [N(CN) 2 ]Br].