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.

Subject headings

NATURVETENSKAP  -- Fysik (hsv//swe)

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

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ref (subject category)

art (subject category)