Abstract
We have been studying the variation of thermodynamic and transport properties as β-(BEDT-TTF) 2 I 3 evolves from the ambient-pressure-cooled, structurally metastable low T c ( β L ) phase to the high T c ( β H ) phase. Annealing at ambient pressure for about a hundred hours near 100 K removes the β L -associated incommensurate superstructure that forms below T 175 (≈175 K at ambient pressure). We find from measurements of the temperature dependent Hall coefficient and heat capacity that long term annealing also suppresses the lower temperature T 20 transition (≈20 K) that occurs in the β L phase, leading to bulk β H phase superconductivity. The results are consistent with the opening of the Fermi surface (FS) at T 20 in non-annealed samples but are not consistent with a 50% reduction in FS area for non-annealed β L phase samples (compared to the area of the Fermi Surface in the β H phase) or significant localization at T 175 . Finally, we compare these results to our measurements of the temperature dependent Hall coefficient and T c under pressure.
Published Version
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