Abstract:A robust zero-energy bound state (ZBS) in a superconductor, such as a Majorana or Andreev bound state, is often a consequence of non-trivial topological or symmetry related properties, and can provide indispensable information about the superconducting state. Here we use scanning tunneling microscopy/spectroscopy to demonstrate, on the atomic scale, that an isotropic ZBS emerges at the randomly distributed interstitial excess Fe sites in the superconducting Fe(Te,Se). This ZBS is localized with a short decay length of ~ 10 Å, and surprisingly robust against a magnetic field up to 8 Tesla, as well as perturbations by neighboring impurities. We find no natural explanation for the observation of such a robust zero-energy bound state, indicating a novel mechanism of impurities or an exotic pairing symmetry of the iron-based superconductivity.Main Text: Superconductivity arises from the macroscopic quantum condensation of electron pairs. The symmetry of the wave-function of these pairs is one of the most essential aspects of the microscopic pairing mechanism. Since the impurity-induced local density of states (DOS) is sensitive to the pairing symmetry, it can be used to test the symmetry of the order parameter and to probe the microscopic pairing mechanism. Being a local probe with atomic resolution, scanning tunneling microscopy/spectroscopy (STM/S) (1) has played a key role in this respect, especially in the study of high-TC cuprate superconductors (2,3).Since its discovery, new compounds of iron-based superconductor (IBSC) continue to be found. However, the pairing symmetry remains a central unresolved issue. So far,

A method, by which periodic two-dimensional arrays of identical metal clusters of nanometer size and spacing could be spontaneously obtained by taking advantage of surface mediated clustering, is reported. The versatility of the method is demonstrated for a broad range of metals on Si(111)-(7 x 7) substrates. In situ scanning tunneling microscopy analysis of In clusters, combined with first-principles total energy calculations, unveils unique initial-stage atomic structures of the surface-supported clusters and the vital steps that lead to the success of this method. A strong interaction between the clusters and the surface holds the key to the observed cluster sizes.

Organic–inorganic hybrid perovskite solar cells are found to be sensitive to moisture, oxygen, UV light, light soaking, heat, electric field, etc.