Critical quadrupole fluctuations and collective modes in iron pnictide superconductors

V. K. Thorsmølle, M. Khodas, Z. P. Yin, Chenglin Zhang, S. V. Carr, Pengcheng Dai, G. Blumberg

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Abstract

The multiband nature of iron pnictides gives rise to a rich temperature-doping phase diagram of competing orders and a plethora of collective phenomena. At low dopings, the tetragonal-to-orthorhombic structural transition is closely followed by a spin-density-wave transition both being in close proximity to the superconducting phase. A key question is the nature of high-Tc superconductivity and its relation to orbital ordering and magnetism. Here we study the NaFe1-xCoxAs superconductor using polarization-resolved Raman spectroscopy. The Raman susceptibility displays critical enhancement of nonsymmetric charge fluctuations across the entire phase diagram, which are precursors to a d-wave Pomeranchuk instability at temperature θ(x). The charge fluctuations are interpreted in terms of quadrupole interorbital excitations in which the electron and hole Fermi surfaces breathe in-phase. Below Tc, the critical fluctuations acquire coherence and undergo a metamorphosis into a coherent in-gap mode of extraordinary strength.

Original languageAmerican English
Article number054515
JournalPhysical Review B
Volume93
Issue number5
DOIs
StatePublished - 16 Feb 2016

Bibliographical note

Publisher Copyright:
© 2016 American Physical Society.

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