Topological insulators (Tis) are a promising candidate for future low-energy electronics technologies, and the 2D or quantum spin hall (QSH) insulator (Bernevig, 2006) has attracted much attention for its 2e^2/h conductance regardless of width. This conductance is characterised by two helical edge states that have correlated spin polarization and momenta (Qi, 2011).
This correlation acts to explicitly prevent backscatter, as a spin-flip is required to scatter into the opposite momentum state. Introduction of magnetic defects breaks time reversal symmetry and allows for such a flip. Therefore, a bath of nuclear spins coupling to the transport electron spins via the hyperfine interaction will disrupt the pristine helical flow. Alternatively, this effect may prove useful, enabling electrical polarization of the bath spins (Bozkurt, 2018). Here we investigate such magnetic defects in the BHZ model using Non-Equilibrium Green’s Functions and look into density and polarization effects.
We find good agreement between Boltzmann and NEGF transport and find that indeed defects oriented collinear to helical edge states are “invisible” to underlying helical states and that antiparallel defects are maximally detrimental.
About the presenter
Jesse Vaitkus is a PhD candidate at RMIT University, studying electron transport in nanodevices using the non-equilibrium Greens function (NEGF) formalism within FLEET’s research theme 1 with Prof Jared Cole. Jesse completed his double BSc. of Nanotechnology and Applied Sciences in 2013 with Distinction, and published his first paper the same year. Jesse completed his Honours degree in 2014, winning the best theory student award.