Giant enhancement of the in-plane critical field for thin Al films via proximity coupling to a topological insulator

Haoyun Deng

Abstract:

A topological superconducting state can be induced in the surface state of a topological insulator (TI) by way
of proximity coupling to a conventional s-wave superconductor (s-SC). Planar s-SC/TI junction structures were
proposed as a scalable platform for controlled generation and manipulation of Majorana zero mode (MZM),
which holds intriguing promise for fault-tolerant quantum computing. Despite intensive research efforts, the
presence of MZM has not been definitively demonstrated in s-SC/TI/s-SC lateral junctions. A key factor is a
lack of direct measurement and quantitative understanding of the proximity coupling between the s-SC and TI.
Here we report evidence for strong superconducting proximity effect between a three-dimensional strong TI and
Al, a conventional s-SC with minimal intrinsic spin-orbit coupling, in the form of pronounced enhancement of
the in-plane critical field (Hc||) of the thin Al. Specifically, the Hc|| of a 6-nm-thick Al film deposited on a TI is
found to be 2.7 times its Pauli limit and about three times that of a simultaneously deposited reference film on
Si/SiO2. The analysis of the Hc|| enhancement within the Maki theory indicates significant induced spin-orbit
interaction in the Al due to electronic coupling to the TI. Our results revealed a pathway for producing SC/TI
devices of high interfacial electrical transparency conducive for MZM generation and manipulation.