Topological Surface Superconductivity via Josephson Coupling in Bi₂Te₃/Nb

Joseph A. Hlevyack^1,2, Syu-You Guan^3*, Yen-Chen Tsui³, Chiao-An Wang³, Wen-Yu Chen³, Meng-Kai Lin^1,2,4, Yao Li^1,2, Soorya Suresh Babu^1,2, Peng Chen⁵, Ro-Ya Liu^1,2,6, Ji-Eun Lee⁷, Jinwoong Hwang^7,8, Shujie Tang^7,9, Yang Bai^1,2, David Flötotto^1,2, Sung-Kwan Mo⁷, James N. Eckstein^1,2, Peter Abbamonte^1,2, Tien-Ming Chuang³, Tai-Chang Chiang^1,2

¹Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
²Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
³Institute of Physics, Academia Sinica, Taipei, Taiwan
⁴Department of Physics, National Central University, Taoyuan, Taiwan
⁵Tsung Dao Lee Institute, Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shanghai Center for Complex Physics, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
⁶National Synchrotron Radiation Research Center, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
⁷Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, USA
⁸Department of Physics, Kangwon National University, Chuncheon, Korea
⁹State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, China

* Presenter:Syu-You Guan, email:r95222038@gmail.com

Since discoveries of protected conducting surface states, topological superconducting qubits have enchanted quantum science as prime elements in future fault tolerant devices, particularly those based on Josephson junctions containing topological insulators. Still, Josephson coupling is often eclipsed by other proximity effects that can dilute topological superconducting pairing at the nontrivial insulator’s boundaries. Here, however, using an ultralow-temperature scanning tunneling microscope, we detect Josephson physics in topological Bi₂Te₃ films on superconducting Nb. At low temperatures, a previously undetected proximity gap varies little with Bi₂Te₃ thickness, and the density of states exhibits normal and superconducting components. Such observations are rationalized via Josephson pair tunneling through the (nearly) insulating Bi₂Te₃ bulk, creating a rare pure topological superconducting sheet. Our findings establish routes towards accessible topological superconducting states in qubits.

Keywords: topological superconductor, Josephson coupling, superconducting proximity effect, scanning tunneling microscope