Synopsis: Ultrathin Superconductors Take a Step Up

Single-atomic-step imperfections on the surface of superconducting films behave like Josephson junctions.
Synopsis figure
S. Yoshizawa et al., Phys. Rev. Lett. (2014)

Metal films that are only an atom or two thick can become superconducting at temperatures near absolute zero. However, in these two-dimensional materials, small imperfections such as one-atom-thick elevation changes (“atomic steps”) may end up blocking the flow of supercurrents. A new study of superconducting vortices in metal films provides the first direct evidence that the atomic steps behave like Josephson junctions—structures made of two superconductors separated by a barrier. The results imply that atomic steps allow supercurrents to flow at a restricted rate, which could make them useful as functional elements in future 2D superconducting devices.

In 2010, physicists found that metal films adsorbed on so-called silicon surface reconstructions could behave as superconductors. The discovery came as a surprise, since quantum fluctuations were expected to disrupt superconductivity in 2D structures. A great deal of research is now devoted to testing how robust this superconductivity is. Atomic steps and other surface defects typically have little effect on bulk (3D) superconductors, but they clearly could influence the behavior of these ultrathin materials.

Takashi Uchihashi of the National Institute for Materials Science in Tsukuba, Japan, and his colleagues performed scanning tunneling microscopy measurements of indium films on reconstructed silicon surfaces. Specifically, the team studied the formation of superconducting vortices—supercurrents traveling around a closed loop that appear in certain superconductors when an external magnetic field is applied. The researchers observed that most of the vortices in the film were circular with a nonsuperconducting inner core. However, the vortices located along atomic steps were elliptical in shape, and their cores were superconducting. Numerical simulations showed that this behavior was consistent with the atomic steps providing a Josephson coupling between different terraces of the film.

This research is published in Physical Review Letters.

–Michael Schirber


More Features »


More Announcements »

Subject Areas

SuperconductivityMaterials Science

Previous Synopsis

Soft Matter

Getting the Wrinkles Out

Read More »

Next Synopsis

Related Articles

Synopsis: Tackling Electronic Correlations
Condensed Matter Physics

Synopsis: Tackling Electronic Correlations

A new “first principles” simulation method could broaden the range of strongly correlated materials whose properties can be theoretically predicted. Read More »

Viewpoint: Hydrogen Hides Surprises at High Pressure
Condensed Matter Physics

Viewpoint: Hydrogen Hides Surprises at High Pressure

Measurements of the melting curve of hydrogen at unprecedentedly high pressures call for a refinement of the theories describing the material. Read More »

Synopsis: Graphene Helps Catch Light Quanta

Synopsis: Graphene Helps Catch Light Quanta

The use of graphene in a single-photon detector makes it dramatically more sensitive to low-frequency light. Read More »

More Articles