Pressure induced high spin-low spin transition in FeSe superconductor studied by x-ray emission spectroscopy and ab initio calculations

FeSe is a simple binary system in the iron based superconducting family and exhibits a significant pressure induced increase in the superconducting transition temperature (T(c)). In addition to pressure effect, spin fluctuations, magnetic ordering, and crystal structure all play vital roles in altering T(c). Even though various experiments and theoretical simulations explain the connection among them and superconductivity, the interplay between these important parameters is still not clearly understood. Here, we report the pressure effect on the spin state of Fe in FeSe superconductor studied using synchrotron x-ray emission spectroscopy at ambient and low temperatures down to 8 K near T(c). Pressure induced high spin to low spin transition was observed at both ambient and low temperatures with continuous suppression of Fe magnetic moments under increasing pressure. The spin transition is closely related to the pressure induced tetragonal to orthorhombic structural transition. (C) 2011 American Institute of Physics. [doi:10.1063/1.3621859]