Charge Dynamics in 122 Iron-Based Superconductors by Aliaksei Charnukha

By Aliaksei Charnukha

This thesis combines hugely exact optical spectroscopy info at the lately stumbled on iron-based high-temperature superconductors with an incisive theoretical research. 3 striking effects are mentioned: (1) The superconductivity-induced amendment of the far-infrared conductivity of an iron arsenide with minimum chemical disease is quantitatively defined via a strong-coupling idea for spin fluctuation mediated Cooper pairing. The formalism built during this thesis additionally describes previous spectroscopic information on extra disordered compounds. (2) an analogous fabrics express a pointy superconductivity-induced anomaly for photon energies round 2.5 eV, orders of importance better than the superconducting power hole. the writer offers a qualitative interpretation of this exceptional commentary, that is in line with the multiband nature of the superconducting country. (3) The thesis additionally develops a entire description of a superconducting, but optically obvious iron chalcogenide compound. the writer indicates that this hugely strange habit should be defined due to the nanoscopic coexistence of insulating and superconducting stages, and he makes use of a mixture of 2 complementary experimental tools - scanning near-field optical microscopy and low-energy muon spin rotation - to without delay photograph the part coexistence and quantitatively verify the part composition. those information have very important implications for the translation of information from different experimental probes.

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By Aliaksei Charnukha

This thesis combines hugely exact optical spectroscopy info at the lately stumbled on iron-based high-temperature superconductors with an incisive theoretical research. 3 striking effects are mentioned: (1) The superconductivity-induced amendment of the far-infrared conductivity of an iron arsenide with minimum chemical disease is quantitatively defined via a strong-coupling idea for spin fluctuation mediated Cooper pairing. The formalism built during this thesis additionally describes previous spectroscopic information on extra disordered compounds. (2) an analogous fabrics express a pointy superconductivity-induced anomaly for photon energies round 2.5 eV, orders of importance better than the superconducting power hole. the writer offers a qualitative interpretation of this exceptional commentary, that is in line with the multiband nature of the superconducting country. (3) The thesis additionally develops a entire description of a superconducting, but optically obvious iron chalcogenide compound. the writer indicates that this hugely strange habit should be defined due to the nanoscopic coexistence of insulating and superconducting stages, and he makes use of a mixture of 2 complementary experimental tools - scanning near-field optical microscopy and low-energy muon spin rotation - to without delay photograph the part coexistence and quantitatively verify the part composition. those information have very important implications for the translation of information from different experimental probes.

Show description

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Extra info for Charge Dynamics in 122 Iron-Based Superconductors

Example text

C Momentum dependence of all superconducting gaps in the out-of-plane direction across several Brillouin zones. Colors indicate the magnitude of the superconducting gap (increasing from green to red). Characteristic points in the Brillouin zone refer to the one-iron unit cell of the Fe sublattice. Adapted with author’s permission from Ref. 5 Superconducting Properties 31 entirety, the existence of multiple electronic bands implies multiple superconducting gaps, and they have indeed been observed; second, the overwhelming majority of the iron-based superconductors exhibit a certain clustering of the magnitudes of the superconducting gaps into two groups.

3. The properties of the minority metallic phase, unlike those of the antiferromagnetic phase, have seen much debate. Even the chemical composition of the metallic phase long remained a mystery. g. Ref. [124]) to the chemical composition of the antiferromagnetic phase but without iron-vacancy order [134]. 5 electron per Fe lattice site (including the iron-vacancy sites), which corresponds to an extremely overdoped case of the 122 iron arsenides, beyond the superconducting dome in Fig. 4 for Ba(Fe1−x Cox )2 As2 .

For example, Fig. 3 Fe2 As2 mapped out with ARPES. Two concentric circular pockets are clearly visible at the point, along with a complex ‘propeller’ structure at the X point of the 1-Fe Brillouin zone. The latter consists of a central electronlike pocket surrounded by four ‘blades’, which have a holelike character and supposedly result from high-temperature Fermi-surface reconstruction due to a nesting instability (good match in their geometrical shape and size) between one of the circular hole pockets at the point and an electron pocket at the X point of the 1-Fe magnetic Brillouin zone (M point of the 2-Fe Brillouin zone corresponding to the real chemical unit cell) [54].

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