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Regular version of the site

Article

Direct observation of ballistic Andreev reflection

Journal of Experimental and Theoretical Physics. 2014. Vol. 119. No. 6. P. 997-1017.
Klapwijk T. M., Ryabchun S.

An overview is presented of experiments on ballistic electrical transport in inhomogeneous super
conducting systems which are controlled by the process of Andreev reflection. The initial experiments based
on the coexistence of a normal phase and a superconducting phase in the intermediate state led to the concept
itself. It was followed by a focus on geometrically inhomogeneous systems like point contacts, which provided
a very clear manifestation of the energy and direction dependence of the Andreev reflection process. The
point contacts have recently evolved towards the atomic scale due to the use of mechanical breakjunctions,
revealing a very detailed dependence of Andreev reflection on the macroscopic phase of the superconducting
state. In presentday research, the superconducting in homogeneity is constructed by clean room technology
and combines superconducting materials, for example, with lowdimensional materials and topological insu
lators. Alternatively, the superconductor is combined with nanoobjects, such as graphene, carbon nano
tubes, or semiconducting nanowires. Each of these “inhomogeneous systems” provides a very interesting
range of properties, all rooted in some manifestation of Andreev reflection.