Fluctuating Cooper pairs in FeSe at temperatures exceeding double T c

Abstract

Temperature dependencies of excess conductivity, , have been studied in detail for three FeSe0.94 textured polycrystalline samples prepared by partial melting and solid state reaction. It was revealed that both and its temperature dependence are extremely sensitive to the method of sample preparation. Then, it was shown that in the range from the superconducting transition temperature T c ~9 K up to the characteristic temperature T 01 ~19 K, obeys the classical fluctuation theories of Aslamazov–Larkin (AL) and Hikami-Larkin (Maki-Thompson (MT) term) pointing to the existence of fluctuating Cooper pairs in FeSe at temperatures exceeding double T c . Like in cuprates, AL–MT crossover at is observed, which means the appearance of 3D–2D dimensional transition at this temperature. This allows us to determine the coherence length along the c-axis, ξ c (0) ~3 Å, and a set of additional samples’ parameters, including the phase relaxation time, , of fluctuating Cooper pairs (FCPs), within a simple two-dimensional free-carrier picture. It was shown that in FeSe coincides with that found for YBa2Cu3O suggesting that the nature of superconducting fluctuations is very similar for these high-temperature superconductors of different types.