中国物理B ›› 2016, Vol. 25 ›› Issue (3): 37301-037301.doi: 10.1088/1674-1056/25/3/037301

• CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES • 上一篇    下一篇

Suppression of Andreev conductance in a topological insulator-superconductor nanostep junction

Yi-Jie Zheng(郑翌洁), Jun-Tao Song(宋俊涛), Yu-Xian Li(李玉现)   

  1. College of Physics & Information Engineering and Hebei Advanced Thin Films Laboratory, Hebei Normal University, Shijiazhuang 050024, China
  • 收稿日期:2015-08-05 修回日期:2015-11-10 出版日期:2016-03-05 发布日期:2016-03-05
  • 通讯作者: Yu-Xian Li E-mail:yxli@mail.hebtu.edu.cn
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 11204065 and 11474085) and the Natural Science Foundation of Hebei Province, China (Grant Nos. A2013205168 and A2014205005).

Suppression of Andreev conductance in a topological insulator-superconductor nanostep junction

Yi-Jie Zheng(郑翌洁), Jun-Tao Song(宋俊涛), Yu-Xian Li(李玉现)   

  1. College of Physics & Information Engineering and Hebei Advanced Thin Films Laboratory, Hebei Normal University, Shijiazhuang 050024, China
  • Received:2015-08-05 Revised:2015-11-10 Online:2016-03-05 Published:2016-03-05
  • Contact: Yu-Xian Li E-mail:yxli@mail.hebtu.edu.cn
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 11204065 and 11474085) and the Natural Science Foundation of Hebei Province, China (Grant Nos. A2013205168 and A2014205005).

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摘要： When two three-dimensional topological insulators (TIs) are brought close to each other with their surfaces aligned, the surfaces form a line junction. Similarly, three TI surfaces, not lying in a single plane, can form an atomic-scale nanostep junction. In this paper, Andreev reflection in a TI-TI-superconductor nanostep junction is investigated theoretically. Because of the existence of edge states along each line junction, the conductance for a nanostep junction is suppressed. When the incident energy (ε) of an electron is larger than the superconductor gap (Δ), the Andreev conductance in a step junction is less than unity while for a plane junction it is unity. The Andreev conductance is found to depend on the height of the step junction. The Andreev conductance exhibits oscillatory behavior as a function of the junction height with the amplitude of the oscillations remaining unchanged when ε=0, but decreasing for ε=Δ, which is different from the case of the plane junction. The height of the step is therefore an important parameter for Andreev reflection in nanostep junctions, and plays a role similar to that of the delta potential barrier in normal metal-superconductor plane junctions.

关键词: topological insulator, nanostep junction, suppression of Andreev conductance

Abstract: When two three-dimensional topological insulators (TIs) are brought close to each other with their surfaces aligned, the surfaces form a line junction. Similarly, three TI surfaces, not lying in a single plane, can form an atomic-scale nanostep junction. In this paper, Andreev reflection in a TI-TI-superconductor nanostep junction is investigated theoretically. Because of the existence of edge states along each line junction, the conductance for a nanostep junction is suppressed. When the incident energy (ε) of an electron is larger than the superconductor gap (Δ), the Andreev conductance in a step junction is less than unity while for a plane junction it is unity. The Andreev conductance is found to depend on the height of the step junction. The Andreev conductance exhibits oscillatory behavior as a function of the junction height with the amplitude of the oscillations remaining unchanged when ε=0, but decreasing for ε=Δ, which is different from the case of the plane junction. The height of the step is therefore an important parameter for Andreev reflection in nanostep junctions, and plays a role similar to that of the delta potential barrier in normal metal-superconductor plane junctions.

Key words: topological insulator, nanostep junction, suppression of Andreev conductance

中图分类号:  (Surface states, band structure, electron density of states)

  • 73.20.At
73.23.-b (Electronic transport in mesoscopic systems) 73.25.+i (Surface conductivity and carrier phenomena) 73.40.-c (Electronic transport in interface structures)