Perfect Andreev reflection due to the Klein paradox in a topological superconducting state

Seunghun Lee; Valentin Stanev; Xiaohang Zhang; Drew Stasak; Jack Flowers; Joshua S Higgins; Sheng Dai; Thomas Blum; Xiaoqing Pan; Victor M Yakovenko; Johnpierre Paglione; Richard L Greene; Victor Galitski; Ichiro Takeuchi

doi:10.1038/s41586-019-1305-1

Perfect Andreev reflection due to the Klein paradox in a topological superconducting state

Nature. 2019 Jun;570(7761):344-348. doi: 10.1038/s41586-019-1305-1. Epub 2019 Jun 19.

Authors

Seunghun Lee^{1

2}, Valentin Stanev^{1

2

3}, Xiaohang Zhang^{1

2}, Drew Stasak¹, Jack Flowers¹, Joshua S Higgins^{2

4}, Sheng Dai⁵, Thomas Blum⁶, Xiaoqing Pan^{5

6

7}, Victor M Yakovenko^{3

4

8}, Johnpierre Paglione^{2

4}, Richard L Greene^{2

4}, Victor Galitski^{3

4

8}, Ichiro Takeuchi^{9

10

11}

Affiliations

¹ Department of Materials Science and Engineering, University of Maryland, College Park, MD, USA.
² Center for Nanophysics and Advanced Materials, University of Maryland, College Park, MD, USA.
³ Joint Quantum Institute, University of Maryland, College Park, MD, USA.
⁴ Department of Physics, University of Maryland, College Park, MD, USA.
⁵ Department of Materials Science and Engineering, University of California, Irvine, CA, USA.
⁶ Department of Physics and Astronomy, University of California, Irvine, CA, USA.
⁷ Irvine Materials Research Institute, University of California, Irvine, CA, USA.
⁸ Condensed Matter Theory Center, University of Maryland, College Park, MD, USA.
⁹ Department of Materials Science and Engineering, University of Maryland, College Park, MD, USA. takeuchi@umd.edu.
¹⁰ Center for Nanophysics and Advanced Materials, University of Maryland, College Park, MD, USA. takeuchi@umd.edu.
¹¹ Department of Physics, University of Maryland, College Park, MD, USA. takeuchi@umd.edu.

PMID: 31217601
DOI: 10.1038/s41586-019-1305-1

Abstract

In 1928, Dirac proposed a wave equation to describe relativistic electrons¹. Shortly afterwards, Klein solved a simple potential step problem for the Dirac equation and encountered an apparent paradox: the potential barrier becomes transparent when its height is larger than the electron energy. For massless particles, backscattering is completely forbidden in Klein tunnelling, leading to perfect transmission through any potential barrier^2,3. The recent advent of condensed-matter systems with Dirac-like excitations, such as graphene and topological insulators, has opened up the possibility of observing Klein tunnelling experimentally^4-6. In the surface states of topological insulators, fermions are bound by spin-momentum locking and are thus immune from backscattering, which is prohibited by time-reversal symmetry. Here we report the observation of perfect Andreev reflection in point-contact spectroscopy-a clear signature of Klein tunnelling and a manifestation of the underlying 'relativistic' physics of a proximity-induced superconducting state in a topological Kondo insulator. Our findings shed light on a previously overlooked aspect of topological superconductivity and can serve as the basis for a unique family of spintronic and superconducting devices, the interface transport phenomena of which are completely governed by their helical topological states.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.
Research Support, Non-U.S. Gov't