Superconductors carry electricity without resistance, but figuring out how their electrons pair up can be difficult. That pairing pattern matters: it can help scientists understand a material’s behavior and identify unusual forms of superconductivity.
In a new study, researchers, including MSE professor, Dr. Petro Maksymovych, used computer simulations to examine a technique called tunneling Andreev reflection spectroscopy. In this process, an electron approaching a superconductor can be reflected as a hole, while another electron joins the superconducting current. By measuring how the tunneling signal changes as the probe moves closer to the material, scientists can separate this process from ordinary electron flow.
The simulations show that the signal depends on the superconductor’s pairing pattern. For example, Andreev reflection strongly shapes the signal for one common pattern, called s-wave, but is suppressed for d-wave. In some patterns where the gap changes sign, Andreev reflection and ordinary electron tunneling can both contribute. Stronger coupling between the probe and material can also bring higher-order processes into play.
The result is a kind of spectral fingerprint: a pattern in the measured signal that could help distinguish superconductors with different pairing structures. Because the technique can be used with a scanning tunneling microscope, it may eventually help researchers examine these properties at nearly atomic resolution.
This work is based on simulations, so it does not establish a new experimental diagnostic on its own. But it gives scientists a clearer guide for interpreting future measurements—and a promising way to investigate superconductors whose pairing patterns remain uncertain.
Citation: Maksymovych, P.; Song, S. Y.; Lawrie, B.; Ko, W.; Lado, J. L. Fingerprinting superconductors by disentangling Andreev and quasiparticle currents across tunable tunnel junctions. Arxiv 2026.
