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Scientists make first direct images of topological insulator’s edge currents

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Posted June 19, 2013
This graphic depicts the tiny loop of a scanning SQUID, or superconducting quantum interference device (silver), which detects magnetic fields (red) created by an edge current (blue) in a topological insulator. Credit: Greg Stewart

This graphic depicts the tiny loop of a scanning SQUID, or superconducting quantum interference device (silver), which detects magnetic fields (red) created by an edge current (blue) in a topological insulator. Credit: Greg Stewart

Researchers at a SLAC/Stanford institute have made the first direct images of electrical currents flowing along the edges of a topological insulator – a recently discovered state of matter with potential applications in information technology.

In these strange solid-state materials, currents flow only along the edges of a sample while avoiding the interior. Using an exquisitely sensitive detector they built, scientists from the Stanford Institute for Materials and Energy Sciences (SIMES) were able to sense the weak magnetic fields generated by the edge currents and tell exactly where the currents were flowing.

“Now no one can doubt that they exist,” said Kathryn A. “Kam” Moler, the SIMES and Stanford University physics professor who led the research, which was published Sunday in Nature Materials.

The scientists surveyed a tiny rectangular piece of mercury telluride, a semiconductor that becomes a topological insulator when cooled to nearly absolute zero in the presence of an electric field.

Post-doctoral researcher Katja Nowack and graduate student Eric Spanton, first and second authors on the team’s research report, scanned the sample surface with a SQUID, or superconducting quantum interference device – a microscope for detecting magnetic fields. The team’s custom-made SQUID was 100 million times more sensitive to magnetic moments than the best commercial version.

Read more at: Phys.org

 

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