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제목: Optical properties of iron-based conductors and superconductors

연사: Prof. Christopher Homes (Condensed Matter Physics and Materials Science Dept., Brookhaven National Laboratory) 

일시: 2014. 4. 21(월) 오후 2:00 ~ 4:00

장소: 삼성학술정보관 7층 Creative learning room

초록: In the high-temperature cuprate superconductors, only a single band is observed at the Fermi level; as a result the optical conductivity may be modeled using a single free-carrier component.  In a simple metal the Drude model usually sufficient; however, electronic correlations and electron-boson coupling in the cuprates require a more generalized form in which the scattering rate and the effective mass are both frequency dependent [1].  The iron-based conductors and superconductors are multiband materials with several bands crossing the Fermi level, resulting in multiple hole and electron pockets at the center and corners of the Brillouin zone, respectively [2].  The presence of multiple bands requires, at a minimum, a “two-Drude” model in which the electron and hole pockets are treated as separate contributions [3]. In general, the two-Drude approach reveals: (i) a strong component associated with the hole pocket with a large scattering rate (nearly incoherent transport) that is essentially temperature independent; (ii) a weaker component associated with the electron pocket whose scattering rate has a strong temperature dependence.  Some recent results using this approach in the pnictide materials BaFe2As2 (TN~138 K) and Ba0.6K0.4Fe2As2 (Tc~38 K) [4] will be discussed, as well as some preliminary findings the iron-chalcogenide systems, Fe1+Te (TN~68 K) and FeTe0.55Se0.45 (Tc~14 K) [5].

*This work done in collaboration with Yaomin Dai, Qiang Li, Jinsheng Wen, Zhijun Xu, Genda Gu, Ricardo Lobo, and Ana Akrap; work supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Contract No. DE-AC02-98CH10886.

[1] A. V. Puchkov, D. N. Basov, and T. Timusk, J. Phys.: Condens. Matter 8, 10049 (1996).
[2] S. Raghu et al., Phys. Rev. B 77, 220503(R) (2008).
[3] D. Wu et al., Phys. Rev. B 81, 100512 (2010).
[4] Y. M. Dai et al., Phys. Rev. Lett. 111, 117001 (2013).
[5] C. C. Homes et al., Phys. Rev. B 81, 180508(R) (2010).