Strong Superconducting Proximity Effect in Pb-Bi2Te3 Hybrid Structures

Abstract

To study the interface between a conventional superconductor and a topological insulator, we fabricated Pb-Bi2Te3-Pb lateral and sandwiched junctions, and performed electron transport measurements down to low temperatures. The results show that there is a strong superconducting proximity effect between Bi2Te3 and Pb, as that a supercurrent can be established along the thickness direction of the Bi2Te3 flakes (100~300 nm thick) at a temperature very close to the superconducting Tc of Pb. Moreover, a Josephson current can be established over several microns in the lateral direction between two Pb electrodes on the Bi2Te3 surface. We have further demonstrated that superconducting quantum interference devices can be constructed based on the proximity-effect-induced superconductivity. The critical current of the devices exhibits s-wave-like interference and Fraunhofer diffraction patterns. With improved designs, Josephson devices of this type would provide a test-bed for exploring novel phenomena such as Majorana fermions in the future.

Nearly flat Andreev bound states in superconductor-topological insulator hybrid structures

“…[19][20][21][22][23]. Gate tunable supercurrent has been observed and argued to be due to the TI surface state [19].…”

“…Gate tunable supercurrent has been observed and argued to be due to the TI surface state [19]. Superconducting quantum interference devices based on such junctions have also been demonstrated [22,24]. Thus the flat Andreev bound states at zero energy, and the zero bias conductance peak in the local density of states, predicted here should be experimentally accessible.…”

Topological Insulator Materials

“…6) It is useful to note that such a proximity-induced superconducting state on the surface of a TI has singlet Cooper pairs, but nonetheless it is topologically nontrivial due to the Berry phase born by the surface Dirac electrons; therefore, such a surface can be considered a 2D topological superconductor. There have been a number of experimental reports to confirm the superconducting proximity effect in the topological surface states, 171,231,[260][261][262][263][264][265][266][267][268] but the existence of Majorana fermions has not been elucidated.…”

Superconductivity in textured Bi clusters/Bi2Te3 films

“…Recently, Koren et al observed that the superconductivity below 2-3 K in Bi 2 Se 3 and Bi 2 Te 2 Se films, which was attributed to proximity-induced local superconductivity by small amounts of superconducting Bi inclusions or segregation to the surface with T c of 6.3 K. 24 Furthermore, the strong superconducting proximity effect in Pb-Bi 2 Te 3 -Pb hybrid structures was also reported, 22 in which a supercurrent can be established through 100-300-nm-thick Bi 2 Te 3 flakes at a temperature of ∼7.2 K. Also, it has been observed that PE-induced superconducting state in Bi 2 Se 3 exists over an extended distance of ∼1 μm away from the Pb-Bi 2 Se 3 interface. 21 In regard to this mechanism, the induced superconducting regions [(adjacent to the Bi clusters/Bi 2 Te-3 interfaces, orange regions in Fig.…”