# Andreev Reflection without Fermi surface alignment in High T$_{c}$-Topological heterostructures

## TL;DR

This study demonstrates that Andreev reflection occurs in high T$_{c}$-topological heterostructures despite Fermi surface mismatch, indicating transparent interfaces can form under these conditions.

## Contribution

It shows that Fermi surface mismatch does not prevent Andreev reflection in heterostructures, expanding understanding of interface transparency in high T$_{c}$ and topological materials.

## Key findings

- Andreev reflection observed despite Fermi surface mismatch
- Magnetic field shifts tunneling features via Doppler effect
- Model with a single parameter explains tunneling into supercurrent

## Abstract

We address the controversy over the proximity effect between topological materials and high T$_{c}$ superconductors. Junctions are produced between Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ and materials with different Fermi surfaces (Bi$_{2}$Te$_{3}$ \& graphite). Both cases reveal tunneling spectra consistent with Andreev reflection. This is confirmed by magnetic field that shifts features via the Doppler effect. This is modeled with a single parameter that accounts for tunneling into a screening supercurrent. Thus the tunneling involves Cooper pairs crossing the heterostructure, showing the Fermi surface mis-match does not hinder the ability to form transparent interfaces, which is accounted for by the extended Brillouin zone and different lattice symmetries.