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Electronic Structure Around a Vortex Core in Iron Pnictide Superconductor

Author: XuJian
Tutor: WangQiangHua
School: Nanjing University
Course: Theoretical Physics
Keywords: High-temperature superconductivity Iron-based superconductor (C , e) with a tight-binding model Band-edge effect Flux core Scanning tunneling microscope
CLC: O511.4
Type: Master's thesis
Year: 2011
Downloads: 28
Quote: 0
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Abstract


Was found in the use of scanning tunneling microscopy (STM) studies the iron phosphorus family of high-temperature superconducting materials Ba0.6K0.4Fe2As2 hole doping exists in flux core at the center of a bound state has a negative bias peak. And when a negative bias peak along the tangent away from the flux core, which is divided into two peaks, and finally with the edge of the energy gap together. The above phenomenon in the flux core center the bias bound state exists. In this paper, the effective lattice model, ultra-large-scale calculations of the electronic structure of the same phase of the s-wave (s -) and anti-phase s-wave (s -) pair of iron phosphorus family of superconductors flux core. The final numerical calculation of the tight-binding model, the above asymmetry bound state comes from the band edge effect. The so-called band-edge effect is the bias conductance peak energy is positive (negative) value depends on the Fermi surface close to the electron or hole with the band bottom (top). The first chapter describes the history of the development of the superconductor. The first section describes the conventional the superconductors and unconventional superconductors, namely the copper oxide superconductors and the newly discovered iron-based superconductors. Section II, made a brief introduction to the pairing mechanism in iron-based superconductors. In the second chapter, the basic principles of the STM and its measurement of the flux state. STM is a quantum tunnel effect principle microscopy. Measurements of superconducting material may be assimilated to a point surface NVS (the ordinary metal - vacuum - superconductor) at both ends of the superconducting tunnel junction bias the response to the current process, and according to the differential conductance to determine the characteristics of the superconducting energy gap size, shape, and the pairing symmetry. STM differential conductance measurements of the superconducting flux state seat in the center of flux core will be bound states appear. STM state of flux in hole-doped iron phosphate family superconductors discovered two major phenomenon, negative bias conductance peak flux core at the center of the bound state, as well as away from the flux core, negative conductance peaks split into two peaks, and finally re-integration into the edge of the energy gap. Chapter III describes the theoretical calculation of the electronic structure of the iron phosphorus family of superconductors near the flux core. Tight-binding model will be used to establish an effective s and s - wave pairing lattice model, and experimental qualitative conclusions. And found that this multi-band non-zero bias conductance peak is not sensitive to the phase of the pairing energy gap wave function. First, consider a simple single-band tight-binding model, in order to conduct research on the electronic structure of flux core near, when the Fermi level close with the top / bottom, the conductance peaks of the negative / positive phenomenon, that is, with a side effect. Subsequently, through the study of more energy band, the iron-based superconductors with model (A), to break the the AB symmetry with lattice model (B), five with three-band model and the most complete band structure model, we found that the band-edge effect still exists. This shows that the nature of the band-edge effect is not due to human errors introduced simplified band, but in itself there is a. In the fourth chapter, a summary of the main results of this paper do.

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CLC: > Mathematical sciences and chemical > Physics > Low Temperature Physics > Superconductivity > Superconductors nature
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