Browsing by Author "Creuzet, Gerard"
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Item Open Access Homogeneous superconducting state at 8.1 K under ambient pressure in the organic conductor β-(BEDT-TTF)2I3(1985) Creuzet, Francois; Creuzet, Gerard; Jerome, Denis; Schweitzer, Dieter; Keller, Heimo J.We report the observation of the first narrow and complete superconducting transition yet obtained in β-(BEDT-TTF)2I3 at 8.1 K and ambient pressure after pressurization up to 1.5 kbar and a release of the helium gas pressure at low temperature. We show experimental evidences indicating that the metastable state giving rise to homogeneous superconductivity at ambient pressure is not stable above 250 K.Item Open Access Thermal expansion of the organic conductor β-(BEDT-TTF)2I3(1986) Hamzic, Bojana; Creuzet, Gerard; Schweitzer, Dieter; Keller, Heimo J.We report high resolution thermal expansion measurements between 1.2 and 300 K along the c*-axis in the organic conductor β-(BEDT-TTF)2I3 where the superconducting properties are strongly dependent on the way the system is prepared in the pressure-temperature diagram. We clearly observed a strong anomaly at 172 K related to the structural phase transition and the resistivity anomalies reported by several groups. The temperature analysis in the low temperature regime is coherent with a phonon dominant contribution. Finally, the presence of small hysteresis in a large region around the transitions seem to indicate why both the pressure and the temperature cycling may stabilize small regions of the high-Tc phase of the system, as observed.Item Open Access Two superconducting phases in the organic conductor : β-(BEDT-TTF)2I3(1987) Creuzet, Francois; Bourbonnais, Claude; Creuzet, Gerard; Jerome, Denis; Schweitzer, Dieter; Keller, Heimo J.We have shown the first stabilization of homogeneous superconductivity in the β-phase of (BEDT-TTF)2I3 at high temperature and ambient pressure. We propose that the crystallographic transition occuring at 1 bar is responsible of the striking reduction of Tc if no pressure is applied. However, the phase corresponding to the room temperature structure (called β-H) is the only one giving rise to the high-Tc superconductivity and can be frozen at low temperature and atmospheric pressure after the Orsay process. It is worth noting that organic superconductivity is very sensitive to slight changes of physical parameters.Item Open Access Two superconducting phases in the organic conductor: β-(BEDT-TTF)2I3(1986) Creuzet, Francois; Bourbonnais, Claude; Creuzet, Gerard; Jerome, Denis; Schweitzer, Dieter; Keller, Heimo J.We have investigated the nature and the stability of the high-Tc(∼8 K) and low-Tc (∼1.5 K)superconducting phases (respectively called β-H and β-L) of the organic conductor β-(BEDT-TTF)2I3. First, by resistivity measurements and following a well-defined temperature-pressure cycling process, we show that the β-H phase is stabilized at ambient pressure and low temperature, exhibiting a very sharp and complete superconducting transition at 8.1 K and 1 bar. Secondly, an AC-susceptibility study reveals that this state is stable and exhibits bulk superconductivity at high Tc and ambient P as long as the sample is not warmed above 125 K. Finally, we present NMR results on the 1H spin-lattice relaxation rate behaviour in both the β-H phase and the β-L phase.