Wednesday, June 19, 2013

1306.4305 (M. Bendele et al.)

Interplay of the electronic and lattice degrees of freedom in
A_{1-x}Fe_{2-y}Se_{2} superconductors under pressure

M. Bendele, C. Marini, B. Joseph, G. M. Pierantozzi, A. S. Caporale, E. Pomjakushina, K. Conder, A. Krzton-Maziopa, T. Irifune, T. Shinmei, S. Pascarelli, A. Bianconi, P. Dore, N. L. Saini, P. Postorino
The local structure and electronic properties of Rb$_{1-x}$Fe$_{2-y}$Se$_2$ are investigated by means of site selective polarized x-ray absorption spectroscopy at the iron and selenium K-edges as a function of pressure. A combination of dispersive geometry and novel nanodiamond anvil pressure-cell has permitted to reveal a step-like decrease in the Fe-Se bond distance at $p\simeq11$ GPa. The position of the Fe K-edge pre-peak, which is directly related to the position of the chemical potential, remains nearly constant until $\sim6$ GPa, followed by an increase until $p\simeq 11$ GPa. Here, as in the local structure, a step-like decrease of the chemical potential is seen. Thus, the present results provide compelling evidence that the origin of the reemerging superconductivity in $A_{1-x}$Fe$_{2-y}$Se$_2$ in vicinity of a quantum critical transition is caused mainly by the changes in the electronic structure.
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