High-resolution scanning tunneling microscope and its adaptation for local thermopower measurements in 2D materials.

We present the design, fabrication and discuss the performance of a new combined high-resolution Scanning Tunneling and Thermopower Microscope (STM/SThEM). We also describe the development of the electronic control, the user interface, the vacuum system, and arrangements to reduce acoustical noise and vibrations. We demonstrate the microscope's performance with atomic-resolution topographic images of highly oriented pyrolytic graphite (HOPG) and local thermopower measurements in the semimetal BiTe.

Signatures of two-dimensional superconductivity emerging within a three-dimensional host superconductor.

Spatial disorder has been shown to drive two-dimensional (2D) superconductors to an insulating phase through a superconductor-insulator transition (SIT). Numerical calculations predict that with increasing disorder, emergent electronic granularity is expected in these materials-a phenomenon where superconducting (SC) domains on the scale of the material's coherence length are embedded in an insulating matrix and coherently coupled by Josephson tunneling. Here, we present spatially resolved scanning tunneling spectroscopy (STS) measurements of the three-dimensional (3D) superconductor BaPb Bi O (BPBO), which surprisingly demonstrate three key signatures of emergent electronic granularity, having only been previously conjectured and observed in 2D thin-film systems.

Phase Separation of Dirac Electrons in Topological Insulators at the Spatial Limit.

In this work we present unique signatures manifested by the local electronic properties of the topological surface state in BiTe nanostructures as the spatial limit is approached. We concentrate on the pure nanoscale limit (nanoplatelets) with spatial electronic resolution down to 1 nm. The highlights include strong dependencies on nanoplatelet size: (1) observation of a phase separation of Dirac electrons whose length scale decreases as the spatial limit is approached, and (2) the evolution from heavily n-type to lightly n-type surface doping as nanoplatelet thickness increases.

Disorder driven metal-insulator transition in BaPb(1-x)Bi(x)O₃ and inference of disorder-free critical temperature.

We performed point-contact spectroscopy tunneling measurements on single crystal BaPb(1-x)Bi(x)O(3) for 0≤x≤0.28 at temperatures T=2-40  K and find a suppression in the density of states at low bias voltages that is characteristic of disordered metals. Both the correlation gap and the zero-temperature conductivity are zero at a critical concentration x(c)=0.