Andreev reflection and bound state formation in a ballistic two-dimensional electron gas probed by a quantum point contact

Hiroshi Irie, Clemens Todt, Norio Kumada, Yuichi Harada, Hiroki Sugiyama, Tatsushi Akazaki, and Koji Muraki
Phys. Rev. B 94, 155305 – Published 12 October 2016
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Abstract

We study coherent transport and bound state formation of Bogoliubov quasiparticles in a high-mobility In0.75Ga0.25As two-dimensional electron gas (2DEG) coupled to a superconducting Nb electrode by means of a quantum point contact (QPC) as a tunable single-mode probe. Below the superconducting critical temperature of Nb, the QPC shows a single-channel conductance greater than the conductance quantum 2e2/h at zero bias, which indicates the presence of Andreev-reflected quasiparticles, time-reversed states of the injected electron, returning back through the QPC. The marked sensitivity of the conductance enhancement to voltage bias and perpendicular magnetic field suggests a mechanism analogous to reflectionless tunneling—a hallmark of phase-coherent transport, with the boundary of the 2DEG cavity playing the role of scatterers. When the QPC transmission is reduced to the tunneling regime, the differential conductance vs bias voltage probes the single-particle density of states in the proximity area. Measured conductance spectra show a double peak within the superconducting gap of Nb, demonstrating the formation of Andreev bound states in the 2DEG. Both of these results, obtained in the open and closed geometries, underpin the coherent nature of quasiparticles, i.e., phase-coherent Andreev reflection at the InGaAs/Nb interface and coherent propagation in the ballistic 2DEG.

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  • Received 11 February 2016
  • Revised 11 September 2016

DOI:https://doi.org/10.1103/PhysRevB.94.155305

©2016 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Hiroshi Irie1,*, Clemens Todt1, Norio Kumada1, Yuichi Harada1,†, Hiroki Sugiyama2, Tatsushi Akazaki1,‡, and Koji Muraki1

  • 1NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
  • 2NTT Device Technology Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan

  • *Corresponding author: irie.hiroshi@lab.ntt.co.jp
  • Present address: Global Innovation Centre, Kyushu University, 6-1 Kasuga-koen Kasuga, Fukuoka 816-8580, Japan.
  • Present address: Department of Social Design Engineering, National Institute of Technology Kochi College, 200-1 Monobe Otsu, Nankoku, Kochi 783-8508, Japan.

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Issue

Vol. 94, Iss. 15 — 15 October 2016

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