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

Abstract

We probe the near Fermi level electronic structure of tunable topological insulator (Bi2Se3)-cuprate superconductor Bi2Sr2CaCu2O 8+δ (Tc ≃ 91 K) heterostructures in their proximity induced superconductivity regime. Our careful momentum space imaging provides clear evidence for a twophase coexistence and a striking lack of any strong d-wave proximity effect expected in this system. Our Fermi surface imaging data identifies 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 Bi2Se3 and Bi2Sr2CaCu2O 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 Bi2Se3/Bi2Sr2CaCu2O 8+δ heterostructures, but also set an upper bound on the proximity induced gap for realizing much sought out Majorana fermion condition in this system.

Theoretical study of large proximity-induceds-wave-like pairing from ad-wave superconductor

“…Based on our results, we suggest the discrepancies between the experiments [14][15][16] are due to different interface coupling strengths between Bi 2 Se 3 and BSCCO across the various samples. The observed gap in Ref.…”

“…The change of the pairing symmetry from d-wave in BSCCO to s-wave-like on the surface states from the proximity effect is claimed to reflect a nontrivial coupling in this system 16 . However, two separate experimental groups 14,15 with similar setups do not reproduce the proximity-induced pairing gap on the Bi 2 Se 3 /BSCCO. Earlier tunneling measurements 13 suggest the proximity induced gap at the interface is dwave.…”

“…The chemical potential µ c exhibiting surface states of Bi 2 Se 3 is estimated to be around 0.4eV for the relevant experiment 15 . Noting that Eq.…”

“…We assume only single metallic layer in the Bi 2 Se 3 in our computation, which can be viewed as one of the two dimensional surfaces of the three dimensional topological insulator Bi 2 Se 3 in contact with BSCCO if the bulk band were insulating. The motivations for forming this heterostructure 7,[14][15][16] is to produce effective p ± ip superconductivity, a form of topological superconductivity, on its interface. The edge modes or vertex states of the topological superconductor host the Majorana modes 7 , the simplest anyon which could be useful for quantum computations.…”

“…Recently, the application of the proximity effect to the surface states of a topological insulator (TI), with the goal to produce the topological superconductivity, has stimulated intense theoretical and experimental effort. In addition to s-wave superconductors 7-10 , d-wave superconductors also show interesting proximity effect on the surface states of a TI 9,[11][12][13][14][15][16] . Wang et al 16 observe a surprisingly large s-wave-like pairing gap on the top surface of a seven-quintuple-layerthick Bi 2 Se 3 film on Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) by using angle-resolved photoemission spectroscopy(ARPES).…”