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

摘要

We probe the near Fermi-level electronic structure of tunable topological-insulator (Bi_2Se_3)/cuprate-superconductor Bi_2Sr_2CaCu_2O_(8+δ) (T_c (≌) 91 K) 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 ((« )△_(BSCCO)). These results correlate with our observation of momentum space separation between the Bi_2Se_3 and Bi_2Sr_2CaCu_2O_(8+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 Bi_2Se_3/Bi_2Sr_2CaCu_2O_(8+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.