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Wednesday, July 10th 2019

1:25 pm:

While signatures of Majorana bound states have been observed in one-dimensional systems, there is an ongoing effort to find alternative platforms that can be easily scalable. In this talk, I will present a novel experimental approach based on two-dimensional materials. Using a Josephson junction made of HgTe quantum well coupled to thin-film aluminum, we can tune between a trivial and a topological superconducting state by applying an in-plane magnetic field and controlling the phase difference ϕ across the junction. First, I will recapitulate our supercurrent measurement in the context of spatially varying order parameter of the induced superconductor. Then, I will delve into the observation of its topological transition by measuring the tunneling conductance at the edge of the junction. At low fields, we observe a minimum in the tunneling spectra near zero bias, consistent with a trivial superconductor. However, as the magnetic field increases, the tunneling conductance develops a zero-bias peak which persists over a range of ϕ that expands systematically with increasing magnetic fields. Our observations are consistent with theoretical predictions for this system and with full quantum mechanical numerical simulations. This work provides a new platform for probing topological superconducting phases which can be generalized to other two-dimensional systems with spin-orbit coupling.

References

H. Ren, F. Pientka, S. Hart, A. T. Pierce, M. Kosowsky, L. Lunczer, R. Schlereth, B. Scharf, E. M. Hankiewicz, L. W. Molenkamp, B. I. Halperin, and A. Yacoby, “Topological superconductivity in a phase-controlled Josephson junction”, Nature (London) 569, 93 (2019). https://doi.org/10.1038/s41586-019-1148-9

S. Hart, H. Ren, M. Kosowsky, G. Ben-Shach, P. Leubner, C. Brüne, H. Buhmann, L. W. Molenkamp, B. I. Halperin, and A. Yacoby, “Controlled finite momentum pairing and spatially varying order parameter in proximitized HgTe quantum wells”, Nature Physics 13, 87 (2017). https://doi.org/10.1038/nphys3877

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