Abstract
Frequency analysis of the rf emission of oscillating Josephson supercurrent is a powerful passive way of probing properties of topological Josephson junctions. In particular, measurements of the Josephson emission enable the detection of topological gapless Andreev bound states that give rise to emission at half the Josephson frequency rather than conventional emission at . Here, we report direct measurement of rf emission spectra on Josephson junctions made of HgTe-based gate-tunable topological weak links. The emission spectra exhibit a clear signal at half the Josephson frequency . The linewidths of emission lines indicate a coherence time of 0.3–4 ns for the line, much shorter than for the line (3–4 ns). These observations strongly point towards the presence of topological gapless Andreev bound states and pave the way for a future HgTe-based platform for topological quantum computation.
- Received 17 August 2016
DOI:https://doi.org/10.1103/PhysRevX.7.021011
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Long sought in high-energy physics, Majorana particles (particles that are their own antiparticles) can emerge in condensed matter systems and are promising candidates for future fault-tolerant quantum computation. They have therefore generated immense experimental and theoretical investigations. To engineer Majorana particles, one may use a topological insulator (a material that behaves as an insulator in its interior but as a conductor on its surface) in combination with superconducting and ferromagnetic materials. Though this recipe is well known, major experimental challenges have hampered the unambiguous demonstration of the existence of Majorana particles and of their properties. We address one of these hurdles by studying superconductivity and electrical currents in the topological insulator mercury telluride (HgTe).
One of the challenges is how to induce superconductivity at the interface between the superconductor and the topological insulator. Insight into this superconductivity can be gained by studying a device known as a Josephson junction, where two superconductors are coupled by a thin insulating barrier. This creates a supercurrent, an electrical current that can flow indefinitely. Special features of this current can reveal properties of the underlying superconductivity. Importantly, the supercurrent in a topological junction is predicted to oscillate at half of the frequency of a nontopological junction. We observe this fractional Josephson effect in a junction formed by connecting superconducting electrodes of aluminum to an HgTe quantum well.
This result establishes HgTe as a propitious platform to create and manipulate Majorana excitations, a prerequisite for a scalable fault-tolerant topological quantum computation.