Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 22: Low-dimensional Systems - Materials

TT 22.3: Talk

Thursday, March 29, 2007, 10:00–10:15, H18

Drude response and evidence of a density-wave state in the β″−(ET)₂SF₅CH₂CF₂SO₃ organic superconductor — •Stefan Kaiser¹, Natalia Drichko¹, Martin Dressel¹, and John Schlueter² — ¹1. Physikalisches Institut, Universität Stuttgart, 70550 Stuttgart, Germany — ²Material Science Division, Argonne National Laboratory, Argonne, Illinois 60439-4831, U.S.A.

The quasi-two-dimensional organic superconductor β″−(ET)₂SF₅CH₂CF₂SO₃ is a prominent example of highly correlated electron systems. It raises interest because it forms a density-wave state around 140 K proposed by [Nam et al., PRL 87, 117001]. Previous optical measurements do not show a Drude contribution. Here we present reflectance measurements at frequencies down to 10 cm⁻¹ and temperatures down to 1.8 K, well below the superconducting transisition T_c=5.2 K. Already at room temperature a Drude behavior is observed which grows for lower temperatures. For light polarized in the high reflecting direction a pronounced gap opens around 200 cm⁻¹ for T<125 K. This we relate to the density-wave-gap driven by the nesting of the quasi-one-dimensional Fermi surface. The gap shows a slight anisotropy.