Superconductivity and electronic fluctuations in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ studied by Raman scattering

Abstract

Using polarization-resolved electronic Raman scattering we study under-doped, optimally-doped and over-doped Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ samples in the normal and superconducting states. We show that low-energy nematic fluctuations are universal for all studied doping range. In the superconducting state, we observe two distinct superconducting pair breaking peaks corresponding to one large and one small superconducting gaps. In addition, we detect a collective mode below the superconducting transition in the B${}_{2g}$ channel and determine the evolution of its binding energy with doping. Possible scenarios are proposed to explain the origin of the in-gap collective mode. In the superconducting state of the under-doped regime, we detect a re-entrance transition below which the spectral background changes and the collective mode vanishes.

11 pages, 6 figures

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Cited by in corpus (7)

• On the Remarkable Superconductivity of FeSe and its Close Cousins
• Short-range nematic fluctuations in Sr1-xNaxFe2As2 superconductors
• Elastoresistance measurements on CaKFe${}_4$As${}_4$ and KCa${}_2$Fe${}_4$As${}_4$F${}_2$ with the Fe site of $C_{2v}$ symmetry
• Interplay between nematicity and Bardasis-Schrieffer modes in the short-time dynamics of unconventional superconductors
• Many-body physics-induced selection rules: application to Raman spectroscopy
• The role of orbital nesting in the superconductivity of Iron-based Superconductors
• Signatures of Bardasis-Schrieffer mode excitation in Third-Harmonic generated currents