Importance of structural distortions in enhancement of transition temperature in FeSe\(_{1-x}\)Te\(_{x}\) superconductors

Temperature (12K \(\le\) T \(\le\) 300K) dependent extended X-ray absorption fine structure (EXAFS) studies at the Fe K edge in FeSe\(_{1-x}\)Te\(_x\) (x = 0, 0.5 and 1.0) compounds have been carried out to understand the reasons for increase in T\(_C\) upon Te doping in FeSe. While local distortions are present near superconducting onset in FeSe and FeSe\(_{0.5}\)Te\(_{0.5}\), they seem to be absent in non superconducting FeTe. Of crucial importance is the variation of anion height. In FeSe\(_{0.5}\)Te\(_{0.5}\), near superconducting onset, the two heights, \(h_{Fe-Se}\) and \(h_{Fe-Te}\) show a nearly opposite behaviour. These changes indicate a possible correlation between Fe-chalcogen hybridization and the superconducting transition temperature in these Fe-chalcogenides.