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Daniel Rosenbach1 Peter Schüffelgen1 Chuan Li2 Tobias Werner Schmitt1 Michael Schleenvoigt1 Abdur Jalil1 Jonas Kölzer1 Benjamin Bennemann1 Umut Parlak1 Gregor Mussler1 Alexander Brinkman2 Detlev Gruetzmacher1 Thomas Schäpers1

1, Forschungszentrum Jülich GmbH, Jülich, , Germany
2, University of Twente, Enschede, , Netherlands

A novel approach on quantum information processing based on exotic Majorana zero modes in solid state matter holds the great promise to perform fault tolerant computations. Extensive error correction being the bottleneck of other solid state qubits, drives the research on these so-called Majorana qubits. Majorana zero modes reside at the interface of a topological insulator (TI) towards a superconductor (SC). Signatures thereof have already been realized based on tunnel-spectroscopy[1], Josephson irradiation[2] as well as Shapiro response[3] measurements on TI-SC hybrid devices.
Here, we present Majorana signatures in low temperature experiments found in Shapiro response measurements. The three dimensional Bi2Te3 topological insulator thin films were grown by molecular beam epitaxy. TI-SC hybrid devices are fabricated under ultra-high vacuum conditions, yielding a very high interface quality. The interface transparency and the characteristic ICRN product of in-situ defined Josephson junctions have been determined to show superior quantities, when compared to ex-situ fabricated devices.
Next to highly transparent interfaces, thin films need being confined to nanostructures for Majorana devices. A preparation technique to selectively define TI nanoribbons is presented. Measurements on these nanoribbons show conductance fluctuations, when a magnetic field is applied Using Fourier analysis, the origin of these oscillations is investigated. Superconductivity has as well successfully been induced in these selectively grown TI nanoribbons in proximity to an ex-situ deposited SC. Shapiro response measurements on the nanoribbon based Josephson devices will be presented.
A combination of both processes, the selective growth of TI nanoribbons as well as the in-situ fabrication of superconductive electrodes has been established. This novel preparation technique does not only allow for high quality Josephson devices but allows to fabricate highly complex TI-SC hybrids, due to its scalability. This will ultimately result in a reproducible process to define in-situ deposited qubit architectures based on selectively deposited TI nanoribbons.

[1] V. Mourik, K. Zuo, S. M. Frolov, S. R. Plissard, E. P. Bakkers, L. P. Kouwenhoven, Signatures of Majorana fermions in hybrid superconductor-semiconductor nanowire devices, Science, 336 (6084), 2012
[2] J. Wiedenmann, E. Bocquillon, R. S. Deacon, S. Hartinger, O. Herrmann, T. M. Klapwijk, L. Maier, C. Ames, C. Brüne, C. Gould, A. Oiwa, K. Ishibashi, S. Tarucha, H. Buhmann and L. W. Molenkamp, 4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions, Nat. Com., 10303, 2016
[3] R. S. Deacon, J. Wiedenmann, E. Bocquillon, F. Dominguez, T. M. Klapwijk, P. Leubner, C. Brüne, E. M. Hankiewicz, S. Tarucha, K. Ishibashi, H. Buhmann and L. W. Molenkamp, Josephson Radiation from Gapless Andreev Bound States in HgTe-Based Topological Junctions, Phys. Rev. X 7, 021011, 2017

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