Three Dimensional Superconductivity in FeSe with Tczero Up to 10.9 K Induced by Internal Strain

Polycrystalline sample FeSe was synthesized by a self-flux solution method which shows a zero resistance temperature up to 10.9 K and a Tconset (90% \rhon, \rhon: normal state resistivity) up to 13.3 K. The decrease of superconducting transition temperature by heat treatment indicates that internal crystallographic strain which plays the same effect as external pressure is the origin of its high Tc. The fluctuation conductivity was studied which could be well described by 3D Aslamazov-Larkin (AL) power law. The estimated value of coherence length \xic=9.2 \AA is larger than the distance between conducting layers (~6.0 \AA), indicating the three-dimensional nature of superconductivity in this compound.