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

doi:10.1088/1674-1056/25/3/037301

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.

Keywords: topological insulator nanostep junction suppression of Andreev conductance

Received: 05 August 2015
Revised: 10 November 2015
Accepted manuscript online:

PACS:	73.20.At	(Surface states, band structure, electron density of states)
	73.23.-b	(Electronic transport in mesoscopic systems)
	73.25.+i	(Surface conductivity and carrier phenomena)
	73.40.-c	(Electronic transport in interface structures)

Fund: 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).

Corresponding Authors: Yu-Xian Li
E-mail: yxli@mail.hebtu.edu.cn

Cite this article:

Yi-Jie Zheng(郑翌洁), Jun-Tao Song(宋俊涛), Yu-Xian Li(李玉现) Suppression of Andreev conductance in a topological insulator-superconductor nanostep junction 2016 Chin. Phys. B 25 037301

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

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