A tunnel junction between helical edge states, realized via a constriction in a quantum spin Hall system, can be exploited to steer both charge and spin current into various terminals. We investigate the effects of disorder on the transmission coefficient Tp of the junction by modeling disorder with a randomly varying (complex) tunneling amplitude Γp=|Γp|exp[iϕp]. We show that, while for a clean junction Tp is only determined by the absolute value |Γp| and is independent of the phase ϕp, the situation can be quite different in the presence of disorder: phase fluctuations may dramatically affect the energy dependence of Tp of any single sample. Furthermore, analyzing three different models for phase disorder (including correlated ones), we show that not only the amount but also the way the phase ϕp fluctuates determines the localization length ξloc and the sample-averaged transmission. Finally, we discuss the physical conditions in which these three models suitably apply to realistic cases.
Physical Review B
- Pub Date:
- September 2014
- Electronic transport in mesoscopic systems;
- Electronic structure of disordered solids;
- Condensed Matter - Mesoscale and Nanoscale Physics
- 14 pages, 7 figures