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Proliferation of upstream neutral modes in the fractional quantum Hall regime
Hiroyuki Inoue , Anna Grivnin , Yuval Ronen , Moty Heiblum , Vladimir Umansky , Diana Mahalu
Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
The fractional quantum Hall effects (FQHE) provide canonical examples of topological phases of matter, which are correlated planar electrons under strong perpendicular magnetic fields. As a channel of chargeless energy transport therein, upstream neutral edge modes, carrying only energy without net charge and counter-propagating to charge modes, were recently observed in hole-conjugate states (filling ν of the nth Landau level between n+½ and n+1, with n=0, 1, 2), and in the even denominator state 5/2. These unique modes are born due to spontaneous edge reconstruction among multiple bare edge channels - as was theoretically predicted only for hole-conjugate states. Inter-channel impurity scattering, accompanied by Coulomb interaction, leads to channel mixing and, consequently, to the emergence of the upstream neutral modes. Unexpected theoretically, here we report the presence of upstream neutral modes in electron-like fractional quantum Hall states, especially in a Laughlin state of ν=1/3, via sensitive shot noise measurements. Furthermore, and, again unexpected, we also observed transport of chargeless bulk energy modes; though weaker than that of the upstream chiral modes. The proliferation of such neutral modes drastically changes the accepted picture of edge channel transport in the QHE regime. Moreover, these observations may shed new light on a source of decoherence, which prevented thus far observing quantum interference and the fractional statistics of fractional quasiparticles.