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Nanoseminar in Physics by: Prof. Floris A. Zwanenburg, MESA+ Institute for Nanotechnology, University of Twente, The Netherlands  

Abstract: Our research at the University of Twente focuses on spin and topological physics in silicon and germanium. We aim at controlling the spin states of individual electrons and holes with the ultimate goal of realizing single spin quantum bits as building blocks for future solid-state quantum computers. We make hybrid superconductor-semiconductor devices with Te and Ge nanowires for topological Josephson junctions [1]. In particular, I will show how we use Ge/Si core/shell nanowires to observe Pauli spin blockade [2-4], and to induce a gate-tuneable Josephson supercurrent with a maximum of ~60 nA [5,6]. Near depletion of the nanowire, the supercurrent is carried by single-particle levels of a quantum dot operating in the few-hole regime [5,7,8]. Secondly, in planar silicon we define low-disorder electron quantum dots with Pd gates [9,10], and depletion-mode hole quantum dots in undoped silicon [11]. We have also realized ambipolar charge sensing by fabricating a single-electron transistor next to a single-hole transistor. Using active charge sensing the single-electron transistor can detect the few-charge regime in the hole quantum dot [12].

References:[1] C. Kloeffel et al., Phys. Rev. B 84, 195314 (2011). [2] M. Brauns et al., Applied Physics Letters 109, p. 143113 (2016). [3] F. Froning et al., Applied Physics Letters 113, p. 073102 (2018). [4] M. Brauns et al., Phys. Rev. B 94, 041441(R) (2016). [5] J. Ridderbos et al., Advanced Materials, 1802257, (2018). [6] J. Xiang et al., Nature Nanotechnology 1, 3 (2006). [7] J. Ridderbos et al., Physical Review Materials, 3, 084803 (2019). [8] J. Ridderbos et al., Nano Letters 20, 1, p. 122 (2020). [9] P. C. Spruijtenburg et al., Nanotechnology, (2018). [10] M. Brauns et al., Scientific Reports 8, 5690, (2018). [11] S. V. Amitonov et al., Applied Physics Letters 112, p. 023102 (2018). [12] A. J. Sousa de Almeida et al., Phys. Rev. B 101, 201301(R) (2020).

Introductory talk: "Nanoporous graphene: A novel platform for carbon nanoelectronics" by Dr Isaac Alcón, Postdoctoral Researcher at Theoretical and Computational Nanoscience Group at ICN2