Probing unconventional superconductivity with tunneling Andreev reflection and decay rate spectroscopy

Unconventional superconductivity is essential for realizing various quantum technologies, such as dissipationless transport and topological quantum computing. However, investigating the nature of unconventional superconductivity is still challenging, because most spectroscopic tools measure single-electron spectral function that only indirectly assess superconducting order parameters. Here, we developed a new spectroscopy based on scanning tunneling microscopy and Andreev reflection, which we call tunneling Andreev reflection (TAR), to directly probe the superconducting order parameters [1,2]. By measuring the relative decay rate, we can distinguish Andreev reflection from single quasiparticle tunneling, whose spectroscopic features reflect the nature of underlying superconductivity. We applied decay rate spectroscopy to various superconductors, including conventional and unconventional ones, and compared them with theoretical calculations to identify pairing symmetry [3]. The results show the potential of TAR as a new tool to directly probe superconducting order parameters and identify pairing symmetry.