Hybridization of sub-gap states in one-dimensional superconductor / semiconductor Coulomb islands
E. C. T. O'Farrell,1 A. C. C. Drachmann,1 M. Hell,1, 2 A. Fornieri,1 A. M. Whiticar,1 E. B. Hansen,1 S. Gronin,3, 4 G. C. Gardener,3, 4 C. Thomas,3, 4 M. J. Manfra,3, 5, 6, 4 K. Flensberg,1 C. M. Marcus,1 and F. Nichele1
1Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute, University of Copenhagen, Denmark
2Division of Solid State Physics and NanoLund,Lund University, Sweden
3Department of Physics and Astronomy and Station Q Purdue, Purdue University, USA
4Birck Nanotechnology Center, Purdue University, USA
5School of Materials Engineering, Purdue University, USA
6School of Electrical and Computer Engineering, Purdue University, USA
The prediction that a topological superconductor might be realized by combining accessible and well understood materials [1, 2] prompted an intense experimental effort into superconductor-semiconductor hybrid systems. We present measurements of one-dimensional superconductor-semiconductor Coulomb islands, fabricated by gate confinement of a two-dimensional InAs heterostructure with an epitaxial Al layer. When tuned via electrostatic side gates to regimes without sub-gap states, Coulomb blockade reveals Cooper-pair mediated transport. When sub-gap states are present, Coulomb peak positions and heights oscillate in a correlated way with magnetic field and gate voltage, as predicted theoretically, with (anti) crossings in (parallel) transverse magnetic field indicating Rashba-type spin-orbit coupling. Overall results are consistent with a picture of overlapping Majorana zero modes in finite wires.
[1] R. M. Lutchyn, J. D. Sau, and S. D. Sarma, Phys. Rev. Lett. 105, 077001 (2010).
[2] Y. Oreg, G. Refael, and F. von Oppen, Phys. Rev. Lett. 105, 177002 (2010).