Origin of the Spin Density Wave Instability inAFe2As2(A=Ba,Sr) as Revealed by Optical Spectroscopy

Abstract

We performed optical spectroscopy measurement on single crystals of BaFe2As2 and SrFe2As2, the parent compounds of FeAs-based superconductors. Both are found to be quite metallic with fairly large plasma frequencies at high temperature. Upon entering the spin-density-wave state, the formation of partial energy gaps was clearly observed with the surprising presence of two different energy scales. A large part of the Drude component was removed by the gapping of Fermi surfaces. Meanwhile, the carrier scattering rate was even more dramatically reduced. We elaborate that the spin-density-wave instability is more likely to be driven by the Fermi surface nesting of itinerant electrons than a local-exchange mechanism.

Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides

“…This orbital differentiation signals that the material is in the vicinity of an orbital selective Mott transition, as proposed previously for other iron pnictides [14], where xy orbital is effectively insulating while other orbitals remain metallic. In Fig.1(b) we also display mass enhancement extracted from optics [15][16][17][18] and ARPES [19][20][21][22][23][24] measurements, and notice a good agreement between our theory and experiment when available. The effective mass extracted from ARPES and optics should be compared with that of the t2g orbitals which contribute most of the spectral weight at low energy.…”

Low-energy interband transitions in the infrared response of Ba(Fe1−xCoxMaršík1, Wang2, Rössle3 et al. 2013Phys. Rev. B318460View full textAdd to dashboardCite

“…The major features of these spectra are similar as in previous reports. 18,[29][30][31] (i) The Drude-like upturn of σ 1 (ω) toward low energy that contains (at least) two contributions due to charge carriers with smaller and larger scattering rates that have been assigned to the electron-and holelike bands, respectively; [18][19][20] (ii) the pronounced tail in the MIR range and the following upturn toward higher energy that were previously interpreted in terms of inelastic scattering of the charge carriers and an interband transition with a maximum around 5500 cm −1 , respectively. 18,20 With decreasing T the Drude peak becomes narrower and for all samples a sizable spectral weight transfer occurs from the MIR region to higher energies, i.e., beyond the band at 5500 cm −1 .…”

The orbital characters of low-energy electronic structure in iron-chalcogenide superconductor K x Fe2−y Se2

“…While the parent compounds of most iron-based superconductors are metallic [2][3][4], the parent compound of K x Fe 2−y Se 2 superconductor is found to be either insulating or semiconducting [5][6][7][8][9]. The insulating parental phase even exhibits certain Mott-insulator signatures, and it is phase separated from the superconducting phase in the K x Fe 2−y Se 2 superconductor at a mesoscopic scale [7,10].…”