Context
Progress in quantum computing stems from major advances in materials science and engineering, and their integration into novel fabrication techniques to develop scalable solid-state qubits architectures. Over the last decade, a plethora of solid-state quantum devices have been developed by combining multiple materials with inherently different properties within the same device - heterogeneous integration. This is a significant challenge in materials science, where quantum device operation with high performance requires a very high purity of the interface between two different materials. Any structural defect and roughness at the interface could compromise the ability to detect and manipulate quantum states in solid-state devices.
Project
The goal of this thesis is to develop a scalable material platform where quantum properties can be engineered simply by tailoring the crystal structure of a single atomic element –
Tin (Sn) – and achieve interfaces with the highest quality. Topological insulator/semimetal phases can be tailored in diamond cubic α-Sn by controlling strain
[1, 2] while body-centered tetragonal β-Sn behaves as a superconductor at temperatures below 4 K
[3]. Currently, a controlled switch between α/β-Sn phases is out of reach in a conventional thin film geometry. This thesis will establish the growth of defect-free one-dimensional (1D) Sn nanowires (NWs) on a Silicon wafer using a molecular beam epitaxy (MBE) system. In NWs a precise control over the growth of α/β-Sn phases (
i.e. topological/superconductor phases) becomes possible, resulting in defect-free atomically-sharp interfaces with the highest structural quality. This will provide a truly
homogeneous integration of multiple states of matter in solid-state quantum devices, paving the way to explore the fundamental processes in topological quantum computation
[4], spintronics
[5], and quantum photonics
[6].
Competences to be acquired (i) Epitaxial growth of Sn NW arrays using MBE and chemical vapor deposition (CVD) tools.
(ii) Structural characterization of the materials down to the atomic-level.
(iii) Fabrication of single NW devices in a cleanroom facility.
(iv) Magneto-transport measurements of the NW device at cryogenic temperatures (<1 K).
Required skills
Background in solid-state physics and materials science, interest in performing experiments in the lab, working in a collaborative team, and contributing to international collaborations.
Starting date Fist quarter of 2025.
PhD fundingThe thesis was funded for its entire duration (3 years).
SupervisorDr. Simone Assali (CEA-IRIG/PHELIQS, Grenoble).
Further reading 1. Elemental Topological Insulator with Tunable Fermi Level: Strained α-Sn on InSb(001).
2. Revisiting the physical origin and nature of surface states in inverted-band semiconductors.
3. Dramatic enhancement of superconductivity in single-crystalline nanowire arrays of β-Sn.
4. Topological Quantum Computation - From Basic Concepts to First Experiments.
5. Switching of a Magnet by Spin-Orbit Torque from a Topological Dirac Semimetal.
6. Josephson junction infrared single-photon detector.
References
[1] A. Barfuss, L. Dudy, M. R. Scholz, H. Roth, P. Höpfner, C. Blumenstein, G. Landolt, J. H. Dil, N. C. Plumb, M. Radovic, A. Bostwick, E. Rotenberg, A. Fleszar, G. Bihlmayer, D. Wortmann, G. Li, W. Hanke, R. Claessen, and J. Schäfer
Elemental Topological Insulator with Tunable Fermi Level: Strained 𝛼-Sn on InSb(001)
Physical Review Letters, 2013
[2] Alexander Khaetskii, Vitaly Golovach, and Arnold Kiefer
Revisiting the physical origin and nature of surface states in inverted-band semiconductors
Physical Review B, 2022
[3] Ying Zhang, Chi Ho Wong, Junying Shen, Sin Ting Sze, Bing Zhang, Haijing Zhang, Yan Dong, Hui Xu, Zifeng Yan, Yingying Li, Xijun Hu & Rolf Lortz
Dramatic enhancement of superconductivity in single-crystalline nanowire arrays of Sn
Scientific Reports, 2016
[4] Ady Stern and Netanel H. Lindner
Topological quantum computation - From basic cConcepts to first experiments
Science, 2013
[5] Jinjun Ding, Chuanpu Liu, Vijaysankar Kalappattil, Yuejie Zhang, Oleksandr Mosendz, Uppalaiah Erugu, Rui Yu, Jifa Tian, August DeMann, Stuart B. Field, Xiaofei Yang, Haifeng Ding, Jinke Tang, Bruce Terris, Albert Fert, Hua Chen, Mingzhong Wu
Switching of a Magnet by Spin-Orbit Torque from a Topological Dirac Semimetal
Advanced Materials, 2021
[6] Evan D. Walsh, Woochan Jung, Gil-Ho Lee, Dmitri K. Efetov, Bae-Ian Wu, K.-F. Huang, Thomas A. Ohki, Takashi Taniguchi, Kenji Watanabe, Philip Kim, Dirk Englund, Kin Chung Fong
Josephson junction infrared single-photon detector
Science, 2021