Recent physics research shows how spin-orbit coupling can rearrange
electronic bands in a solid to make a "topological insulator" a new
quantum phase of matter that is guaranteed to have conductive surfaces
even though its bulk is insulating. What happens if you take a
topological insulator and compress or expand it? A team of researchers
at the University of Pennsylvania has examined this question. They find
that if you expand the material enough, you can manipulate the Dirac
points in the electronic structure and force the material to revert to a
conventional insulator. The authors contrast the effects of mechanical
stress with "chemical stress" induced by replacing ions with similar
ions of larger size. They find that chemical stress is more complicated
than mechanical stress, and that the specific chemistry of each ion in
the material determines its topological band structure. This gives new
guidance for how to harness this new state of matter for applications
in spintronics, catalysis, and quantum computing.
The Valence and conduction energy bands of Bi2Se3
in the (111) plane during the phase transition from topological
insulator to conventional insulator. With increasing strain the
topological band gap closes, forming a Dirac point, and then reopens as
conventional band gap.
