Direct Observation of Nodes and Twofold Symmetry in FeSe Superconductor

• Published in: Science (American Association for the Advancement of Science) Vol. 332; no. 6036; pp. 1410 - 1413
• Main Authors: Song, Can-Li, Wang, Yi-Lin, Cheng, Peng, Jiang, Ye-Ping, Li, Wei, Zhang, Tong, Li, Zhi, He, Ke, Wang, Lili, Jia, Jin-Feng, Hung, Hsiang-Hsuan, Wu, Congjun, Ma, Xucun, Chen, Xi, Xue, Qi-Kun
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 17.06.2011; The American Association for the Advancement of Science
• Subjects: Anisotropy; Atoms; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure; Electronics; Electrons; Exact sciences and technology; Imaging; Iron; Josephson effect; Magnetic fields; Materials science; Nanostructure; Nanostructured materials; Observation; Pairing symmetries; Physics; Properties of type I and type II superconductors; Quasiparticles; Reconstruction; Sampling bias; Spectral energy distribution; Spectroscopy; Stoichiometry; Superconductivity; Superconductors; Symmetry; Theory and models of superconducting state; Stoichiometry; Vacancies; Bound state; Iron selenides; Iron based selenides; Scanning tunneling microscopy; Quasiparticles; Energy gap; Electronic structure; Superconductors; Adatoms; Pairing symmetry; Scanning tunneling spectroscopy; Pairing
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1202226

We investigated the electron-pairing mechanism in an iron-based superconductor, iron selenide (FeSe), using scanning tunneling microscopy and spectroscopy. Tunneling conductance spectra of stoichiometric FeSe crystalline films in their superconducting state revealed evidence for a gap function with nodal lines. Electron pairing with twofold symmetry was demonstrated by direct imaging of quasiparticle excitations in the vicinity of magnetic vortex cores, Fe adatoms, and Se vacancies. The twofold pairing symmetry was further supported by the observation of striped electronic nanostructures in the slightly Se-doped samples. The anisotropy can be explained in terms of the orbital-dependent reconstruction of electronic structure in FeSe.