Strain tunes surface electron states of TIs
Several academic institutions collaborated on a research that examined the electronic properties of ultra-thin films of topological insulators (TIs) and developed a method to control the surface electronic states for use in energy-efficient spintronic devices.
Topological insulators are new materials with surfaces that host a new quantum state of matter and are insensitive to contaminants, defects, and impurities. Surface electrons in TIs behave like massless Dirac particles in a similar way to electrons in graphene. Moreover, surface currents in topological insulators also preserve their spin orientation and coherence on a macro scale.
At the York-JEOL Nanocentre, scientists from participating institutions—University of York, University of Wisconsin, and University of Cadiz—demonstrated that tensile strain can lift the topological order, while compressive strain can shift in energy the characteristic Dirac point. The researchers used Scanning Tunnelling Microscopy from Wisconsin and aberration corrected Transmission Electron Microscopy from York.
"These inherent properties of TIs, and the interplay between magnetism and proximity to superconductors, make topological insulators a prime platform for the realisation of solid state quantum computing devices," explained Vlado Lazarov of York's Department of Physics. "The ability to control the surface electronic state of the TIs is a crucial step in realising their potential in energy efficient devices. Through our research, we have shown that it is possible to tune the properties using strain."
Professor Lian Li, from UW-Milwaukee, said, "Using these advanced microscopes, we examined the low-angle tilt grain boundaries in Bi2Se3 (0001) films and found that they consist of arrays of alternating edge dislocation pairs."
Along the boundary, these dislocations introduce different types of strain compressive and tensile.
"Through further tunnelling spectroscopy measurements and quantum mechanical calculations, we discovered that Dirac states are enhanced under tensile strain and destroyed under compressive strain," explained Prof. Li. "These findings suggest new ways to control TIs electronic properties, for example, by applying stress."
- Paul Buckley
EE Times Europe
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