Andreev reflection without Fermi surface alignment in high-T_cvan der Waals heterostructures

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 d + 8and materials with different Fermi surfaces (Bi 2 Te 3 andgraphite). Both cases reveal tunneling spectra that areconsistent with Andreev reflection. This is confirmed by a 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 thatthe Fermi surface mismatch does not hinder the ability to form transparent interfaces, which is accounted for by the extended Brillouin zone and different lattice symmetries.

Andreev Reflection and Klein Tunneling in High-Temperature Superconductor/Graphene Junctions

“…This variation expected due to the sensitivity of the proximity-effect due to fabrication nonuniformities. Comparable magnitude of ∆ i has been seen in BSCCO heterojunctions with other 2D materials [7,22]. We have observed that the amplitude of conductance oscillations decreases with increase in temperature up to 40 K. This observation is consistent with the temperature dependence of ∆ i reported by others [22].…”

“…Bi 2 Sr 2 Ca 1 Cu 2 O 8+δ (BSCCO) is a layered high-temperature superconductor that has a pseudogap of 40 meV [4]. Proximity-induced superconductivity in graphene and topological insulators from BSCCO has shown to induce a superconducting gap of 15-20 meV [5][6][7]. Characterizing the transport across a BSCCO/graphene junction in response to bias, gating, and temperature can reveal new scattering mechanisms which are important for fundamental understanding and enabling applications such as high-temperature Josephson junctions.…”

Superconducting Proximity Effect in d‐Wave Cuprate/Graphene Heterostructures

“…Using topological insulators grown on a d-wave superconductor and ARPES the groups of T. Valla and Z. Hasan [143,163] concluded that the proximity effect is prohibited in these structures due to Fermi surface mismatch. Burch's group, based on exfoliated dwave/TI devices, transport experiments [164] and theory [14] showed the opposite. To our knowledge, no other topological insulator in proximity with d-wave superconductors has been studied so far, which might be due to the growth conditions making it difficult to combine both class of materials.…”

“…However, as we detail below, ad hoc techniques have recently allowed relieving some of those constraints, enabling the experiential demonstration of the proximity effect in graphene in contact with superconducting cuprates [11][12][13] as well as proximity between graphite and bismuth strontium calcium copper oxide (BSCCO). [14] The above ideas are unfolded hereafter, the review being organized as follows: the specificities of graphene and d-wave superconductors are summarized in Sections 1.1 and 1.2, where in addition the motivation for mixing both types of materials in proximity devices is rationalized. A theoretical section follows (Section 2), which first focuses on the particularities of the proximity effect between d-wave superconductors and trivial metals (Section 2.1) and then on those of the proximity between Dirac materials and conventional superconductors (Section 2.2).…”

Andreev Reflection and Klein Tunneling in High-Temperature Superconductor-Graphene Junctions

“…Bi 2 Sr 2 Ca 1 Cu 2 O 8þδ (BSCCO) is a layered high-temperature superconductor that has a pseudogap of 40 meV [5][6][7]. Proximity-induced superconductivity in graphene and topological insulators from BSCCO has shown to induce a superconducting gap of 15-20 meV [8][9][10]. Characterizing the transport across a BSCCO-graphene junction in response to bias, gating, and temperature can reveal new scattering mechanisms which are important for fundamental understanding and enabling applications such as high-temperature Josephson junctions.…”