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

• Published in: Chinese physics B Vol. 25; no. 3; pp. 338 - 341
• Main Author: 郑翌洁 宋俊涛 李玉现
• Format: Journal Article
• Language: English
• Published: 01.03.2016
• Subjects: Conductance; Deltas; Nanostructure; Planes; Reflection; Three dimensional; Topology; Unity; 三维拓扑; 平面结; 振荡行为; 电导; 绝缘体; 超导体; 超导能隙; 钛表面
• ISSN: 1674-1056; 2058-3834; 1741-4199
• DOI: 10.1088/1674-1056/25/3/037301

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. Be- cause of the existence of edge states along each line junction, the conductance for a nanostep junction is suppressed. When the incident energy （e） of an electron is larger than the superconductor gap （A）, 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 e = 0, but decreasing for e = A, 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.