Title: Majorana fermions in Topological Insulator Platforms (MajoranaTopIn)
PI: Yoichi Ando
Grant No. 741121
Period: May 2017 – April 2022 (60 months)
Total Budget: EUR 2,406,250

General Summary of the project

Majorana fermions were recently discovered in topological superconductors as exotic quasiparticles having the curious property of being their own antiparticles. They are not only interesting as novel relativistic quasiparticles, but are also useful for realizing fault-tolerant quantum computers, which would revolutionize the future information technologies. However, currently available platforms to materialize Majorana fermions are limited, and the existing platforms have respective drawbacks for actually building qubits for a scalable quantum computer. Also, various unusual properties are predicted for Majorana fermions, but few have been experimentally addressed. To make a leap in the Majorana-fermion research which is technically highly demanding, one needs to grow state-of-the-art materials and tightly combine them with mesoscopic device research. By performing such an integrated research efforts in the same laboratory and by focusing on topological insulators as the materials basis, this project aims to explore new platforms for Majorana qubits and to establish new methodologies to address peculiar physics of Majorana fermions.

Publications

1. Andrea Bliesener, Junya Feng, A. A. Taskin, and Yoichi Ando, Superconductivity in Sn_1-xIn_xTe thin  films grown by molecular beam epitaxy, Phys. Rev. Materials 3 (2019) 101201(R)-(1-5) (Rapid Communications).
2. Ran Tao, Ya-Jun Yan, Xi Liu, Zhi-Wei Wang, Yoichi Ando, Qiang-Hua Wang, Tong Zhang, and Dong-Lai Feng, Direct Visualization of the Nematic Superconductivity in Cu_xBi₂Se₃, Phys. Rev. X 8 (2018) 041024-(1-9).
3. Subhamoy Ghatak, Oliver Breunig, Fan Yang, Zhiwei Wang, Alexey A. Taskin, and Yoichi Ando, Anomalous Fraunhofer Patterns in Gated Josephson Junctions Based on the Bulk-Insulating Topological Insulator BiSbTeSe₂, Nano Lett. 18 (2018) 5124-5131.

Recent Highlight

We have optimized the technology to fabricate topological insulator (TI)-based Josephson junction with Al as the superconducting (SC) electrode, and our devices present a record-high transparency of 0.8 at the TI/SC interface. This progress has yielded a publication in Nano Letters. In these Josephson-junction devices, we were able to tune the chemical potential of the TI surface states to the Dirac point by back gating and to demonstrate that a finite supercurrent is maintained even at the Dirac point, which is important for the future Majorana devices. In addition, we have elucidated in these devices that the anomalous Fraunhofer patterns often observed in TI-based Josephson junctions are mainly due to inhomogeneous supercurrent distributions within the junction, and it is not in itself a signature of Majorana states.