A van der Waals Heterojunction Approach to the Superconducting Proximity Effect

The superconducting proximity effect is a topic of ongoing interest. Its application to topological insulators could lead to exotic forms of superconductivity that are fundamentally interesting and potentially useful. Because topological materials are often air sensitive and also prone to surface damage, the coupling to a superconductor requires careful management of the interfaces. In this talk, I will describe our efforts in creating gentle, lithography-free, van der Waals-transfer based approaches in creating and probing proximitized heterostructures. Supported by the Penn State MRSEC, our team developed the methods to synthesize and measure the surface of (Bi,Sb)₂Te₃/graphene/Ga thin films, where Ga is the superconductor and the interfaces are atomically sharp. We constructed a clean graphite/thin h-BN tunnel junction inside a glovebox, transferred it to the (Bi,Sb)₂Te₃/graphene/Ga film and used transport tunneling spectroscopy to show clear signatures of proximity-induced superconductivity in the Dirac surface state of the (Bi,Sb)₂Te₃ film and discrete tunneling conductance jumps that correspond to the addition of a single vortex (Li et al, Nat. Mater. 22, 570–575 (2023). We also developed a “via” contact approach to create a clean, van der Waals-like interface between a 3D superconductor and a 2D material. NbN-graphene-NbN Josephson junctions made this way show gate-tunable supercurrent and performance comparable to conventional methods (Li et al, submitted). These transfer-based methods offer a lithography-free, damage-free, and glovebox compatible approach to the studies of superconductivity at sensitive surfaces and interfaces.

In collaboration with:
Cequn Li, Yifan Zhao, Alex Vera, Hemian Yi, Shalini Kumari, Zijie Yan, Chengye Dong, Tim Bowen, Ke Wang, H. Wang, Jessica Thompson, Danielle Reifsnyder Hickey, Joshua Robinson, Cuizu Chang, Penn State University
Omri Lesser, Yuval Oreg, The Weizmann Instutite of Science, Israel
K. Watanabe and T. Taniguchi, The National Institute for Materials Science, Japan

This work is supported by the Penn State Materials Research Science and Engineering Center under award NSF-DMR 2011839.