Probing helicity and the topological origins of helicity via non-local Hanbury-Brown and Twiss correlations

摘要

Quantum Hall edge modes are chiral while quantum spin Hall edge modes arehelical. However, unlike chiral edge modes which always occur in topologicalsystems, quasi-helical edge modes may arise in a trivial insulator too. Thesetrivial quasi-helical edge modes are not topologically protected and thereforeneed to be distinguished from helical edge modes arising due to topologicalreasons. Earlier conductance measurements were used to identify these helicalstates, in this work we report on the advantage of using the non local shotnoise as a probe for the helical nature of these states as also theirtopological or otherwise origin and compare them with chiral quantum Hallstates. We see that in similar set-ups affected by same degree of disorder andinelastic scattering, non local shot noise "HBT" correlations can be positivefor helical edge modes but are always negative for the chiral quantum Hall edgemodes. Further, while trivial quasi-helical edge modes exhibit negativenon-local "HBT" charge correlations, topological helical edge modes can showpositive non-local "HBT" charge correlation. We also study the non-local spincorrelations and Fano factor for clues as regards both the distinction betweenchirality/helicity as well as the topological/trivial dichotomy for helicaledge modes.