Gapless Andreev bound states in the quantum spin Hall insulator HgTe

Abstract

In recent years, Majorana physics has attracted considerable attention in both theoretical and experimental studies due to exotic new phenomena and its prospects for fault-tolerant topological quantum computation. To this end, one needs to engineer the interplay between superconductivity and electronic properties in a topological insulator, but experimental work remains scarce and ambiguous. Here we report experimental evidence for topological superconductivity induced in a HgTe quantum well, a two-dimensional topological insulator that exhibits the quantum spin Hall effect. The ac Josephson effect demonstrates that the supercurrent has a $4\pi$-periodicity with the superconducting phase difference as indicated by a doubling of the voltage step for multiple Shapiro steps. In addition, an anomalous SQUID-like response to a perpendicular magnetic field shows that this $4\pi$-periodic supercurrent originates from states located on the edges of the junction. Both features appear strongest when the sample is gated towards the quantum spin Hall regime, thus providing evidence for induced topological superconductivity in the quantum spin Hall edge states.

arXiv comment16 pages, 5 figures (main text) + 11 pages, 4 figures (SI)

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• $4\pi$-periodic Josephson supercurrent in HgTe-based topological Josephson junctions
• Induced Superconductivity in the Quantum Spin Hall Edge
• Spin polarization of the quantum spin Hall edge states
• High Kinetic Inductance Superconducting Nanowire Resonators for Circuit QED in a Magnetic Field
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• Edge-mode Superconductivity in a Two Dimensional Topological Insulator
• AC Josephson effect in finite-length nanowire junctions with Majorana modes
• Helical edge and surface states in HgTe quantum wells and bulk insulators
• Dynamical detection of Majorana fermions in current-biased nanowires
• Fermion-parity anomaly of the critical supercurrent in the quantum spin-Hall effect
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• Dynamics of Majorana States in a Topological Josephson Junction
• Phenomenology and Dynamics of Majorana Josephson Junction
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• Influence of Topological Edge States on the Properties of Al/Bi2Se3/Al Hybrid Josephson Devices
• Ac Josephson Effect in Topological Josephson Junctions
• Revealing topological superconductivity in extended quantum spin Hall Josephson junctions
• Quantum interference of edge supercurrents in a two-dimensional topological insulator
• Effects of spin-orbit coupling and spatial symmetries on the Josephson current in SNS junctions
• Even-odd flux quanta effect in the Fraunhofer oscillations of an edge-channel Josephson junction

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