Coulomb blockade and Coulomb staircases in CoBi nanoislands on SrTiO3(001).

We successfully fabricated two-dimensional metallic CoBi nanoislands on SrTiO3(001) substrate by molecular beam epitaxy, and systematically investigated their electronic structures by scanning tunneling microscopy and spectroscopyin situat 4.2 K. Coulomb blockade and Coulomb staircases with discrete and well-separated levels are observed for the individual nanoisland, which is attributed to single-electron tunneling via two tunnel junction barriers. They are in excellent agreement with the simulations based on orthodox theory. Furthermore, we demonstrated that the Coulomb blockade becomes weaker with increasing temperature and almost disappears at ∼22 K in our variable temperature experiment, and its full-width at half-maximum of dI/dVpeaks with temperature is ∼6 mV. Our results provide a new platform for designing single-electron transistors that have potential applications in future microelectronics.

Coexistence of Superconductivity and Nontrivial Band Topology in Monolayered Cobalt Pnictides on SrTiO3.

As an intrinsically layered material, FeSe has been extensively explored for potentially revealing the underlying mechanisms of high transition temperature (high-Tc) superconductivity and realizing topological superconductivity and Majorana zero modes. Here we use first-principles approaches to identify that the cobalt pnictides of CoX (X = As, Sb, Bi), none of which is a layered material in bulk form. Nevertheless, all can be stabilized as monolayered systems either in freestanding form or supported on the SrTiO3(001) substrate. We further show that each of the cobalt pnictides may potentially harbor high-Tc superconductivity beyond the Cu- and Fe-based superconducting families, and the underlying mechanism is inherently tied to their isovalency nature with the FeSe monolayer. Most strikingly, each of the monolayered CoX's on SrTiO3 is shown to be topologically nontrivial, and our findings provide promising new platforms for realizing topological superconductors in the two-dimensional limit.

One-Dimensional Frenkel Chain Defects in CsBi4Te6.

Understanding the detailed process of spontaneous formation of intrinsic defects and their ability to tune the electronic structures in functional materials has become a key prerequisite for their technological applications. Here, by using in situ scanning tunneling microscopy, we report the observation of one-dimensional Frenkel chain defects on the cleaved CsBi4Te6 surface due to the migration of Te atoms for the first time. Further scanning tunneling spectroscopy measurements clearly revealed a self-electron doping effect of the Frenkel chain defects, which could directly affect their thermoelectric and superconducting properties. The unique one-dimensional Frenkel tellurium atomic chain defect and its doping effect on the electronic structure observed here not only shed light on tuning the electric properties of a series of tellurides but also possess profound implications for enriching the microscopic details of defect chemistry and materials science.