Electron tunneling through a potential barrier is a single-particle quantum effect. The probability of tunneling exponentially depends on the thickness of the barrier (along the tunneling direction), which is why the tunneling current through the gap between the tip and the sample surface is highly sensitive to the gap width. For this reason, if the tunneling current is kept constant while the tip is moved along the surface at a distance of about 0.1 nm from it, a map of the surface topography with subatomic resolution can be obtained.

For the invention of the scanning tunneling microscope (STM), G. K. Binnig and H. Rohrer were awarded the Nobel Prize in 1986.

An even more important mode of operation involves measuring the local current-voltage characteristic (I-V) of the tunnel junction, the derivative of which (dI/dV) provides information about the local density of states in the sample under study. The figures show examples of (dI/dV) measurements while scanning the tip along the surface of the superconductor NbSe₂ and the topological insulator Bi₂Se₃. In the first case, the revealed symmetry of the electron wave function is visible, while in the second case, features at the energy of the Dirac point (DP), the bottom of the conduction band (BCB), and the top of the valence band (BVB) are observed.

A tunnel junction can be formed in the material under investigation using the “break-junction” method. For this purpose, a microcrack is created in the sample in a controlled manner, resulting in two “banks” of the same material connected by a tunnel junction. This technique allows for the creation and study of “S-N-S” and “S-I-S” type tunnel junctions, enabling the investigation of current-voltage characteristics (I-V) and the dependence of differential conductance (dI/dV) in the contact area. From these measurements, several critical characteristics of superconductors can be extracted, such as the quality and magnitude of energy gaps in the spectrum, as well as their anisotropy and temperature evolution.

The experiments setup is made by laboratory staff and have outstanding characteristics. Additionally, the laboratory is developing methods for creating and studying micro- and nanoscale tunnel mesostructures. Using UV- lithography and electronic lithography, tunneling contacts are fabricated on samples as small as a few microns in size, while focused ion beam (FIB) etching enables sample cuts with nanosized precision. Such structures exhibit better homogeneity and more pronounced crystallographic anisotropy compared to their macroscopic counterparts.