The Study Of Point-contact Spectroscopy In Fe-pnictide Superconductors

The Fe-based superconductors is another type of new high-temperature super-conductors different from the cuprate high-temperature superconductors, it provided a newplatform for the study of high-temperature superconducting mechanism, where the keyproblem is to determine the symmetry of the electron pairing. Although more and moreexperiments show that the Fe-based superconductor iss±wave pairing, but point-contactspectroscopy experiments found that not only the zero-bias conductance peak, but also thevariety of coherent peaks with different samples and the direction of the interface. And itis different compared with thes±-wave symmetry. The point-contact spectroscopy is animportant experiment to determine the pairing symmetry, and the zero-bias conductancepeak is an important basis for determining the cuprate superconductors d-wave pairing.How to understand the experimental results of the point-contact spectroscopy in Fe-basedsuperconductor to determine the pairing symmetry is the purpose of this article.When the Fe-based superconductors iss±-wave pairing, there is the zero energybound state in a specific direction on the surface and the bound state is caused thecoupling between the two band, it is similar to zero energy bound state of d-wavesuperconductors in the [110] direction. The bound state is very sensitive to the surfacedirection, and they exist only in a small area near the [100] direction, the energy of thebound state exists in the other direction is a finite energy. We used two methods to provethe existence of the bound state and compared the experimental results.The paper is organized as following: first the paper introduced the research status ofFe-based superconductors, focusing on various experimental results and theoreticalanalysis of the point-contact spectroscopy, and given the specific issue of the paper. Thenthe paper introduced the basic theory, including the Bogoliubov-de Gennes(BdG) equationand Blonder-Tinkham-Klapwijk(BTK) basic theory. Then the two-band model and methodwere introduced, and the conditions for the existence of the zero energy bound states isobtained through used approximate to calculate the BdG equation of the superconductingsystem. The surface bound states of different interface were discussed when the Fe-based superconductors is thes±-wave pairing. And within the framework of the BTK theory, thepaper used a simplified model obtained the tunneling conductance formula. Thecalculation results were compared with the experimental datas to explain the relationshipbetween the different experimental results and bound state. Finally, the paper summarizedand gived conclusions.