Condensed Matter Seminars

Motivated by recent experimental observations of unconventional superconductivity in twisted bilayer and trilayer graphenes, we develop a theory describing the differential conductance between a normal STM tip and a 2D superconductor with an arbitrary gap structure. Our analytical scattering theory accounts for Andreev reflections, which become prominent at larger transmission between the tip and the superconductor. Exploiting the dependence of Andreev reflection on the relative position of the STM tip with respect to the lattice symmetry points, we show that the structure of the superconducting gap can be extracted by combining weak- and strong-tunneling limits of differential conductance. Furthermore, the theory incorporates a tip/impurity-induced scattering potential within the 2D material, which allows us to describe subgap resonances.