Andreev Reflection in Scanning Tunneling Spectroscopy of Unconventional Superconductors

Abstract

We evaluate the differential conductance measured in a scanning tunneling microscopy (STM) setting at arbitrary electron transmission between an STM tip and a two-dimensional (2D) superconductor with arbitrary gap structure. Our analytical scattering theory accounts for Andreev reflections, which become prominent at larger transmissions. We show that this provides complementary information about the superconducting gap structure beyond the tunneling density of states, strongly facilitating the ability to extract the gap symmetry and its relation to the underlying crystalline lattice. We use the developed theory to discuss recent experimental results on superconductivity in twisted bilayer graphene.

6+8 pages, 2+1 multi-panel figures; published version

References in corpus (5)

• Flat Bands in Slightly Twisted Bilayer Graphene
• Evidence for unconventional superconductivity in twisted bilayer graphene
• High-temperature topological superconductivity in twisted double layer copper oxides
• Pairing symmetry of twisted bilayer graphene: a phenomenological synthesis
• Current- and field-induced topology in twisted nodal superconductors

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• Phonon-mediated intrinsic topological superconductivity in Fermi arcs
• Probing superconductivity with tunneling spectroscopy in rhombohedral graphene
• Andreev reflection in normal metal/charge-4e superconductor junctions
• Tunneling spectra of impurity states in unconventional superconductors
• Atomic scale imaging of sign-changing order parameter in superconducting FeSe with Tunneling Andreev Reflection
• Momentum-resolved spectroscopy of superconductivity with the quantum twisting microscope