Polarization Resolved Raman Spectroscopy Reveals Excitonic Plasma Pairing Glue in the Iron Pnictide Superconductorsby Tommy on 24/10/2014
Critical Charge Fluctuations in Iron Pnictide Superconductors, V. K. Thorsmølle, M. Khodas, Z. P. Yin, Chenglin Zhang, S. V. Carr, Pengcheng Dai and G. Blumberg
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 concomitant spin density wave transition both being in close proximity to the superconducting phase. A key question is the microscopic mechanism 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 shows critical non-symmetric charge fluctuations across the entire phase diagram associated with a hidden ordered state. The charge fluctuations are interpreted in terms of plasma waves of quadrupole intra-orbital excitations in which the electron and hole Fermi surfaces breath in-phase. Below Tc, these plasmons undergo a metamorphosis into a coherent ingap mode of extraordinary strength and at the same time serve as a glue for non-conventional superconducting pairing.
This paper comes with a companion paper discussing some of the parent compounds.
On the origin of the electronic anisotropy in iron pnicitde superconductors, W.-L. Zhang, P. Richard, H. Ding, Athena S. Sefat, J. Gillett, Suchitra E. Sebastian, M. Khodas and G. Blumberg
We use polarization-resolved Raman spectroscopy to study the anisotropy of the electronic characteristics of the iron-pnictide parent compounds AFe2As2 (A = Eu, Sr). We demonstrate that above the structural phase transition at Ts the dynamical anisotropic properties of the 122 compounds are governed by the emergence of xy-symmetry critical collective mode foretelling a condensation into a state with spontaneously broken four-fold symmetry at a temperature T*. However, the mode’s critical slowing down is intervened by a structural transition at Ts, about 80 K above T*, resulting in an anisotropic density wave state.
Well this is going to throw a wrench is some people’s gears. Mechanisms schmeckanisms.
As Mr. Spock would say – fascinating.