Impurity bound-state as a probe of order-parameter symmetry in iron-pnictide superconductors: T-matrix approach

10th International Conference on Materials and Mechanisms of Superconductivity

Ogata, Masao^1 ; Kariyado, Toshikaze^1

Department of Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan^1

关键词: Bogoliubov-de Gennes equations;    Bound state;    Density of state;    Iron pnictide superconductors;    Multiple structures;    Numerical results;    Order parameter symmetry;    Particle-hole asymmetry;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/449/1/012018/pdf
DOI  :  10.1088/1742-6596/449/1/012018

来源: IOP

【 摘 要 】

The impurity induced in-gap bound state in multi-orbital superconductors is discussed based on Bogoliubov-de Gennes equation and T-matrix approximation. It is shown that multiple bound states appear depending on the strength of the impurity potential in the case of unconventional s-wave (or s+ - wave) superconductivity. This result can be used to distinguish between the conventional s-wave and unconventional s-wave states. T-matrix approximation using a simplified model supports the numerical results obtained in the Bogoliubov-de Gennes equation. It is shown that the T-matrix can be block diagonalized when we use orbital representation. As a result, each orbital can make the impurity bound state independently, leading to the multiple structure of the bound states. From the analysis of the T-matrix approximation, we understand the reasons why the bound states always appear pair-wise at the positions of ±ω and why there is a large asymmetry of the two peaks. We also show that the particle-hole asymmetry of the density of states gives rise to the asymmetry with respect to the strength of the impurity potential. The connection between the obtained results and the iron-pnictide superconductors is also provided.