Physics

Upon (Andreev) Reflection

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Science  17 Mar 2000:
Vol. 287, Issue 5460, pp. 1889
DOI: 10.1126/science.287.5460.1889c

Transistor devices containing a semiconductor-superconductor interface would combine the facile control of carrier concentration in the semiconductor with the low-dissipation and low-noise properties of the superconductor. As an electron passes from the semiconductor into the superconductor, it must form a Cooper pair with another electron. A hole, which is created to maintain charge-neutrality, is then retroreflected back along the path of the incoming electron in a process known as Andreev reflection. However, interfaces are not perfect, and most of the incident electrons are specularly reflected, which makes the magnitude of the induced supercurrent difficult to control and limits potential device applications.

Jakob et al. have directly determined the probability of Andreev reflection. They use a point contact to inject a known current of ballistic electrons toward the interface region. The geometry of their device is such that only the retroreflected holes have a high probability of making it back to the point contact region for detection. With this technique, they determine an Andreev reflection probability of 20%. The quantification of Andreev reflection at the semiconductor-superconductor interface raises the prospect of designing and fabricating well-characterized integrated semiconductor-superconductor devices.—ISO

Appl. Phys. Lett.76, 1152 (2000).

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