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Volume 570 Issue 7761, 20 June 2019

Freedom of movement

In this week’s issue, Ichiro Takeuchi and his colleagues present evidence for the perfect transmission of electrons through a contact barrier between a normal metal and a topological superconductor. The work represents the observation of Klein tunnelling, a relativistic effect in which a particle can move through a barrier between two materials as if the barrier simply wasn’t there. Once an electron (gold sphere) has tunnelled through the barrier, it picks up a partner electron to form a Cooper pair (seen in the cover image at the far side of the tunnel). As a result, a negatively charged hole (black sphere) is reflected back from the barrier. Generally, there is some scattering of electrons at the barrier suppressing this process. But at the barrier with a topological superconductor, electron scattering is completely forbidden. Perfect electron tunnelling and the hole reflection therefore lead to exact doubling of the conductance, which the team’s results confirm. The researchers found that perfect transmission occurred regardless of the origin of the contact barrier and suggest that the finding could be useful in quantum information processing.

Cover image: Emily Edwards/Joint Quantum Institute

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