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Title: Optical properties of A Fe 2 As 2 ( A = Ca , Sr, and Ba) single crystals

The detailed optical properties have been determined for the iron-based materials A Fe 2 As 2 , where A = Ca , Sr, and Ba, for light polarized in the iron-arsenic (a-b) planes over a wide frequency range, above and below the magnetic and structural transitions at T N = 138 , 195, and 172 K, respectively. The real and imaginary parts of the complex conductivity are fit simultaneously using two Drude terms in combination with a series of oscillators. Above T N, the free-carrier response consists of a weak, narrow Drude term, and a strong, broad Drude term, both of which show only a weak temperature dependence. Below T N there is a slight decrease of the plasma frequency but a dramatic drop in the scattering rate for the narrow Drude term, and for the broad Drude term there is a significant decrease in the plasma frequency, while the decrease in the scattering rate, albeit significant, is not as severe. The small values observed for the scattering rates for the narrow Drude term for T $$\ll$$ T N may be related to the Dirac conelike dispersion of the electronic bands. Below T N new features emerge in the optical conductivity that are associated with the reconstruction Fermi surface and the gapping of bands at Δ 1 ≃ 45 – 80 meV, and Δ 2 ≃ 110 – 210 meV. In conclusion, the reduction in the spectral weight associated with the free carriers is captured by the gap structure; specifically, the spectral weight from the narrow Drude term appears to be transferred into the low-energy gap feature, while the missing weight from the broad term shifts to the high-energy gap.
 [1] ;  [2] ;  [3] ;  [3] ;  [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). Condensed Matter Physics and Materials Science Dept.
  2. Univ. of Geneva (Switzerland)
  3. Ames Lab. and Iowa State Univ., Ames, IA (United States). Dept. of Physics and Astronomy
Publication Date:
Report Number(s):
BNL-113461-2017-JA; IS-J-9159
Journal ID: ISSN 2469-9950; PRBMDO; R&D Project: PO016; KC0202020; TRN: US1701213
Grant/Contract Number:
SC0012704; AC02-07CH11358
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 94; Journal Issue: 19; Journal ID: ISSN 2469-9950
American Physical Society (APS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States); Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Swiss National Science Foundation (SNSF)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1333342; OSTI ID: 1342913