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Thursday, 03 January 2013

Structural disorder affects electron spin in topological insulators

Publishing in Physical Review Letters, ICREA Research Professor Stephan Roche and colleagues describe the relationship between bulk disorder and surface spin texture in topological insulators.

Topological insulators are a fascinating new class of materials that, since their experimental discovery in 2007, have garnered massive attention among researchers. Now, scientists at ICN have taken a step forward in understanding how the structure of topological insulators affects the way that electrons behave inside of them.Dr David Soriano, Dr Frank Ortmann and ICREA Research Professor Dr Stephan Roche, of ICN’s Theoretical and Computational Nanoscience Group, have just published an article in Physical Review Letters in which they unveil a close relationship between bulk disorder (i.e. structural imperfections) and randomisation of the spin texture of surface states in topological insulator thin films.Physicists are racing to understand—and ultimately, exploit—the bizarre behaviour of topological insulators, whose combined insulating/conducting behaviour offers promise for future electronics applications, such as quantum computing. In bulk form, topological insulators have a non-trivial band gap, but their surface states are gapless—in other words, a three-dimensional portion of these materials insulates at its inside (bulk area) but conducts electricity at its surfaces. Experimental researchers use a technique called spin-polarised angle resolved photoemission spectroscopy (SPARPES) to study electron spin behaviour at surfaces.By developing a suitable model, the ICN team analysed the changes in spin texture (i.e. the way that electron spin changes over space and time) in simulated topological insulator thin films as a function of increasing bulk disorder. They showed that the spin polarisation in these materials steadily randomises with increasing disorder and eventually vanishes, as the boundary that typically demarcates spin behaviour at the surface from that at the interior gradually dissolves. Basically, the more pure the structure, the more pure the separation between internal (bulk) electron behaviour and surface electron behaviour. Their results may pave the way for future SPARPES analysis studies of bulk crystallinity in topological insulator thin films.To access the article, “Three-dimensional Models of Topological Insulator Films: Engineering of Dirac Cones and Robustness of Spin Texture”, click here.