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UID:UW-Physics-Event-2007
DTSTART:20101213T180000Z
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DTSTAMP:20260414T124945Z
LAST-MODIFIED:20101129T205536Z
LOCATION:5310 Chamberlin
SUMMARY:Electronic correlations in the optical properties of the iron-
 based superconductors\, R. G. Herb Condensed Matter Seminar\, Christop
 her Homes\, Brookhaven National Lab
DESCRIPTION:The complex conductivity of the iron-arsenic superconducto
 r BaFe<sub>1.85</sub>Co<sub>0.15</sub>As<sub>2</sub> (T<sub>c</sub> â‰
 … 25 K) and the iron-chalcogenide superconductor FeTe<sub>0.55</sub>Se
 <sub>0.45</sub> (T<sub>c</sub> ≅ 14 K) have been determined over a w
 ide frequency range for light polarized in the planes at a variety of 
 temperatures above and below T<sub>c</sub>. The optical properties of 
 the superconducting materials are compared with their metallic parent 
 compounds\, BaFe<sub>2</sub>As<sub>2</sub> and Fe<sub>1.03</sub>Te. De
 spite being multiband systems\, the low-frequency conductivity in the 
 electron-doped iron-arsenic material is dominated by a single (electro
 n) pocket\, which can be described by a simple Drude model. Not surpri
 singly\, the electron-boson coupling constant λ ≅ 1\, indicating th
 at this material is not strongly correlated. Below T<sub>c</sub> there
  is a clear signature of the superconductivity in the optical conducti
 vity and there is evidence that more than one energy scale is involved
  in the superconductivity. However\, at low temperature (T << T<sub>c<
 /sub>) less than 50% of the free carriers have collapsed into the cond
 ensate indicating that this material is not in the clean limit [1]. In
  contrast\, the low-frequency conductivity of the iron-chalcogenide co
 mpounds is non-Drude at low temperature\, with λ ≅ 5 - 7 in the sup
 erconducting material\, indicating a much greater degree of electronic
  correlation. Below T<sub>c</sub> there is once again evidence for two
  energy scales in the superconductivity - this may be interpreted as e
 ither the isotropic gapping of the electron and hole pockets\, or the 
 anisotropic gapping of the electron pocket (s<sup>+/-</sup> model) [2]
 . Both the iron-arsenic and the iron-chalcogenide materials fall close
  to the universal scaling line for a BCS dirty-limit superconductor in
  the weak-coupling limit\, as do the majority of the high-temperature 
 copper-oxide superconductors.<br>
\n<br>
\n[1] J. J. Tu et al.\, Phys.
  Rev. B <b>82</b>\, 174509 (2010).<br>
\n[2] C. C. Homes et al.\, Phys
 . Rev. B <b>81</b>\, 180508(R) (2010)\; J. Phys. Chem. Solids (in pres
 s).
URL:https://www.physics.wisc.edu/events/?id=2007
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