Fermi-level electronic structure of a topological-insulator/cuprate- superconductor based heterostructure in the superconducting proximity effect regime

We probe the near Fermi-level electronic structure of tunable topological-insulator (Bi2Se3)/cuprate-superconductor Bi2Sr2CaCu2O8+δ (Tc≃91K) heterostructures in their proximity-induced superconductivity regime. Our careful momentum space imaging provides clear evidence for a two-phase coexistence and a striking lack of any strong d-wave proximity effect expected in this system. Our Fermi surface imaging data identify key contributors in reducing the proximity-induced gap below the 5 meV or to a lower energy range (ΔBSCCO). These results correlate with our observation of momentum space separation between the Bi2Se3 and Bi2Sr2CaCu2O8+δ Fermi surface topologies and mismatch of lattice symmetries in addition to the presence of a small coherence length. These studies not only provide critical momentum space insights into the Bi2Se3/Bi2Sr2CaCu2O8+δ heterostructures, but also set an upper bound on the proximity-induced gap for realizing a much sought out Majorana fermion condition in this system.