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Optical properties of Ba122 iron-based superconductors

Abstract : When a mass of atoms are brought together to form a solid state material, many and various novel phenomena arise in the material due to the strong interactions among nuclei and electrons. For example, spin-density-wave (SDW) or charge-density-wave (CDW) occurs at low temperature in anisotropic, lowdimensional materials or in metals with high density of states at the Fermi level. Superconductivity is exhibited by certain materials when cooling it down to a critical temperature. All these phases can dominate the material solitarily or coexist with each other in one material, indeed, strong coupling or competition may exist among these phases when coexisting with each other in one material. The driving mechanism of these phases and the relations between them are always the center of interest when they are discovered in a new material. Ba1−xKxFe2As2 and Ba(Fe1−xCox)2As2 were discovered as a new family of high-Tc superconductors, the Ba122 system iron-based superconductor. The parent compound of this family is BaFe2As2 which undergoes a spin-density-wave (SDW) transition at about 138 K. When doping the parent compound with holes [Ba1−xKxFe2As2] or electrons [ Ba(Fe1−xCox)2As2], the magnetism is suppressed and superconductivity emerges in this material. In a considerably large doping scale, the SDWphase and superconductivity coexist with each other. In this case, the superconducting paring symmetry and the relations between the coexistent orders in the Ba122 system materials are highly desired. In this thesis, we studied the optical properties of the hole [Ba1−xKxFe2As2] and electron [ Ba(Fe1−xCox)2As2] doped Ba122 system iron-based superconductors. In the optimally K and Co doped samples, we found di erent low frequency optical response. By comparing the optical properties and the doping sites of these two optimally doped samples, we provided strong evidence for an s± pairing symmetry in Ba122 system iron-based superconductors. In the underdoped Ba1−xKxFe2As2 samples, we observed a smaller partial energy gap besides the SDW and superconducting gaps. We studied the temperature and doping dependence of the three gaps, combined with a spectral weight analysis, we concluded that the smaller partial energy gap shares the same electronic states with superconducting condensate, a precursor scenario is preferred for the smaller partial gap. In contrast, the SDW transition depletes the electronic states available for superconducting condensate, acting as a competitive order to the superconductivity.
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Submitted on : Tuesday, September 18, 2012 - 9:55:51 AM
Last modification on : Wednesday, October 14, 2020 - 3:43:08 AM
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  • HAL Id : pastel-00733150, version 1

Citation

Yaomin Dai. Optical properties of Ba122 iron-based superconductors. Superconductivity [cond-mat.supr-con]. Université Pierre et Marie Curie - Paris VI; Chinese Academy of Sciences, 2011. English. ⟨pastel-00733150⟩

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