Origin of pressure induced second superconducting dome in AyFe(2-x)Se(2) [A = K, (TI, Rb)]

• Recent observation of a pressure induced second superconducting phase in A(y)Fe(2-x)Se(2) [A = K, (TI, Rb)] calls for the models of superconductivity that are rich enough to allow for multiple superconducting phases. We propose the model where pressure induces renormalization of band parameters in such a way that it leads to changes in Fermi surface topology even for a fixed electron number. We develop a low-energy effective model, derived from first-principles band-structure calculation at finite pressure, to suggest the phase assignment where a low pressure superconducting state with no hole pocket at the 0 point is a nodeless d-wave state. It evolves into a s(+/-) state at higher pressure when the Fermi surface topology changes and the hole pocket appears. We analyze the pairing interactions using a five band tight binding fitted band structure and find that a strong pairing strength is dependent on pressure. We also evaluate the energy and momentum dependence of neutron spin resonances in each of the phases as verifiable predictions of our proposal.

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NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

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