2018/10/15 by Mingyang Chen, Qingkun Tang, Xiaoyu Chen +8 · 18 citations
Business, Management and Accounting · Materials Science · Mathematics · Physics and Astronomy · #Band gap #Condensed matter physics #Cooper pair #Corporate Taxation and Avoidance #Electron #Fermi surface #Iron-based superconductors research #Mathematics #Pairing #Physics #Quantum mechanics #Quasiparticle #Rare-earth and actinide compounds #Sign (mathematics) #Superconductivity #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.99.014507
published in Physical review. B./Physical review. B 99(1) (American Physical Society) · 10 pages, 6 figures
arxiv created 2018/10/15 · openalex created_date 2018/10/26 · openalex publication_date 2019/01/10 · arxiv updated 2019/01/16 · openalex updated_date 2026/08/05
In many unconventional superconductors the pairing of electrons is driven by the repulsive interaction, which leads to the sign reversal of superconducting gaps along the Fermi surfaces or between them. However, to measure this sign change is not easy and straightforward. It is known that, in superconductors with sign reversal gaps, nonmagnetic impurities can break Cooper pairs leading to the quasiparticle density of states in the superconducting state. The standing waves of these quasiparticles will interfere with each other leading to the quasiparticle interference (QPI) pattern which carries the phase message reflecting also the superconducting gap structure. Based on the recently proposed defect-bound-state QPI technique, we explore the applicability of this technique to a typical iron-based superconductor FeTe0.55Se0.45 with roughly equivalent gap values on the electron and hole pockets connected by the wave vector q2=(0,\ensuremathπ). It is found that, on the negative energy side, with the energy slightly below the gap value, the phase reference quantity |g(q,\ensuremath-E)|cos(\ensuremathθq,+E\ensuremath-\ensuremathθ_q,\ensuremath-E) becomes negative and the amplitude is strongly enhanced with the scattering vector q2, but that corresponding to the scattering between the electron-electron pockets, namely q3=(\ensuremathπ,\ensuremathπ), keeps all positive. This is well consistent with the theoretical expectation of the s^\ifmmode±\else\textpm\fi pairing gap and thus serves as a direct visualization of the sign reversal gaps. This experimental observation is also supported by the theoretical calculations with the Fermi surface structure and s^\ifmmode±\else\textpm\fi pairing gap.