K. Douglas Carlson

Organic Superconductors—New Benchmarks

Recent advances in the design and synthesis of organic synthetic metals have yielded materials that have the highest superconducting transition temperatures (Tc ≈ 13 kelvin) reported for these systems. These materials have crystal structures consisting of alternating layers of organic donor molecules and inorganic anions. Organic superconductors have various electronic and magnetic properties and crystal structures that are similar to those of the inorganic copper oxide superconductors (which have high Tc values); these similarities include highly anisotropic conductivities, critical fields, and short coherence lengths. The largest number of organic superconductors, including those with the highest Tc values, are charge-transfer salts derived from the electron donor molecule BEDT-TTF or ET [bis(ethylenedithio)-tetrathiafulvalene]. The synthesis and crystal structures of these salts are discussed; their electrical, magnetic, and band electronic structure properties and their many similarities to the copper oxide superconductors are treated as well.

New cation-anion interaction motifs, electronic band structure, and electrical behavior in .beta.-(ET)2X salts [ET = bis(ethylenedithio)tetrathiafulvalene; X = dichloroiodide, chlorobromoiodide]

Etude structurale des composes du titre. Determination des temperatures de transition metal-isolant

Correlations of Anion Size and Symmetry with the Structure and Electronic Properties of β-(BEDTTTF)2X Conducting Salts with Trihalide Anions X = 13-, 12Br-, 1Br2-

Abstract In the isostructural series of β-(BEDT-TTF)2X organic metals, abbreviated β-(ET)2X, where X is a trihalide anion, I3-, I2Br- or IBr2-, and where ET is bis-(ethylenedithio) tetrathiafulvalene (C10S8H8), the salt containing the disordered asymmetric I2Br- anion has atypical structural and electronic properties compared to those containing the symmetrical and ordered I-3 and IBr2- anions.

Ambient pressure superconductivity at 4–5 K in β-(BEDT-TTF)2AuI2

Abstract Crystals of β-(BEDT-TTF) 2 AuI 2 , derived from the sulfur-based organic donor bis(ethylenedithio) tetrathiafulvalene [BEDT-TTF or “ET”] have been synthesized by electrocrystallization and studied by rf penetration depth measurements at ambient pressure and at temperatures down to 0.45 K. The crystals were found to be superconducting at ambient pressure with T c = 3.93–4.98 K, which represent the highest values of T c thus far observed at ambient pressure for an organic superconductor. Measurements of the upper critical field anisotropy are reported.

The first organic cation-radical salt superconductor (Tc= 4 K) with an organometallic anion: superconductivity, synthesis and structure of κL-(BEDT-TTF)2Cu(CF3)4·TCE

Superconductivity at ambient pressure with onset Tc= 4.00 ± 0.05 K is reported in a unique organic cation-radical salt κL-(ET)2Cu(CF3)4·TCE, [ET = bis(ethylenedithio)tetrathiafulvalene, TCE = 1,1,2-trichloroethane] with the Cu(CF3)4– species being the first Cu3+ and F containing organometallic anion in an organic superconductor.

The crystal structures and physical properties of polymeric (BEDT-TTF)-metallothiocyanates

The crystal structures of two new ET metallothiocyanates [ET or BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene] with polymeric anions are presented: (ET)Cu2(SCN)3 and (ET)Agx(SCN)2 (x = ⋍ 1.6). The former is a second, semiconducting, phase in the ETCuSCN system which also yields superconducting κ-(ET)2Cu(NCS)2 (Tc = 10.4 K).

Inductive And Resistive Studies Of The Ambient Pressure Organic Superconductor β-(BEDT-TTF)2I3

Abstract Inductive studies based on rf penetration depth measurements and resistive studies based on 4-lead electrical resistivity measurements are reported for the sulfur-based ambient pressure superconductor β-(BEDT-TTF)2I3. The inductive studies show that the bulk superconducting transition temperature (Tc) is sample dependent, with values of Tc ranging from 1.2 K to 1.4 K. The critical magnetic fields Hc2 show considerable anisotropy in directions perpendicular and parallel to the crystallographic ab plane. The electrical resistivity as a function of temperature shows linear and quadratic dependences on T and unusual structure near 8 K and 4 K.

Superconducting and Electrical Properties of (Bedt-Ttf)2I3 at Ambient Pressure

Abstract Studies of the of field penetration depths and electrical conductivity are described for the sulfur-based ambient pressure organic superconductor (BEDT-TTF)2I3.

Superconductivity above 2 K At Ambient Pressure in Iododibromide (IBr2 −) Charge-Transfer Salts of Bis (ETHYLENEDITHIO) TETRATHIAFULVALENE, BEDT-TTF

Abstract Crystals of the charge-transfer salt (BEDT-TTF)2IBr2, derived from the sulfur-based organic donor bis(ethylenedithio) tetrathiafulvalene [BEDT-TTF], have been synthesized by electrocrystallization and studied by rf penetration depth measurements at ambient pressure and temperatures down to 0.45 K. One of two phases was found to be superconducting with Tc = 2.3-2.8 K. This phase, denoted as β-(BEDT-TTF)2 IBr2, is isostructural with the superconducting triiodide salt, β-(BEDT-TTF)2I3. Evidence for the existence of a metastable superconducting phase of the BEDT-TTF/IBr2 system with Tc near 4.2 K is given.

ESR Studies of Two BEDT-TTF Based Organic Superconductors, θ-(BEDT-TTF)2I3 and ι-(BEDT-TTF)4Hg2.89Br8

Abstract Variable temperature ESR measurements were carried out on two BEDT-TTF, or ET based organic superconductors, θ-(ET)2I3 and κ-(ET)4Hg2.89 Br8. The line widths of the former salt range from 60 to 80 G at room temperature and decrease with decreasing temperature. The line widths of the latter salt range from 69 to 83 G and increase with decreasing temperature. The spin susceptibilities of both salts are temperature independent. The ESR properties of these two salts are compared with those of other ET based materials.