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Abstract: In the quantum Hall effect regime, taking place in a two-dimensional-electrongas under strong magnetic field, currents flow along the edges of the sample.For some particle-hole conjugate states of the fractional regime, e.g., withfilling between 1-2 and 1 of the lowest Landau level; early predictionssuggested the presence of counter-propagating edge currents in addition to theexpected ones. When this did not agree with the measured conductance, it wassuggested that disorder and interactions will lead to counterpropagating modesthat carry only energy - the so called neutral modes. In addition, a neutralupstream mode Majorana mode was also expected for selected wavefunctionsproposed for the even denominator filling 5-2. Here we report on the directobservation of counter-propagating neutral modes in fillings 2-3, 3-5 and 5-2.This was done by injecting such modes and allowing them to impinge on a narrowconstriction, which partly reflected them, with two main observed effects: aA resultant shot noise proportional to the applied voltage on the injectingcontact; b With simultaneously injecting also a charge mode, the presence ofthe neutral mode was found to significantly affect the Fano factor and thetemperature of the backscattered charge mode. In particular, such observationfor filling 5-2, may single out the non-abelian wavefunctions for the state.



Autor: Aveek Bid, Nissim Ofek, Hiroyuki Inoue, Moty Heiblum, Charles Kane, Vladimir Umansky, Diana Mahalu

Fuente: https://arxiv.org/







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