Integer and Fractional Helical States in the Quantum Hall Effect regime

by Yuval Ronen

at Condensed Matter Seminar

Mon, 05 Jun 2017, 11:30
Physics building (#54) room 207

Abstract

In recent years efforts to observe helical edge states in materials with large spin orbit coupling have accelerated These material once in proximity to an s wave superconductor may under certain conditions manifest a topological superconductive TS phase 1 Consequently Majorana fermions allusive quasiparticles with a non Abelian exchange statistic are expected to emerge Even more interesting are the fractional helical states previously not observed which manifest the more exotic para fermion anyons Though evidence for the presence of Majorana fermions accumulates observations of helical edge transport being a prerequisite for the formation of Majorana quasiparticles are scarce Encouraged by proposals that induce topological superconductivity in 2DEG at the quantum Hall effect QHE regime 2 3 we succeeded to form such the sought after robust chiral helical edge modes in GaAs AlGaAs heterostructures In order to have two adjacent counterpropagating edge modes with opposite spin the 2DEG is embedded in a unique quantum well structure which hosts two weakly interacting electronic sub bands Gating the 2DEG with two half plain gates enable a scenario where two different filling factors are applied to the lower and upper sub bands Landau levels of different sub bands cross at the interface between the two gates thus forming overlapping counter propagating chiral edge modes Two counter propagating edges with opposite spins both in the integer and fractional regime were observed propagating for more than 300 microns without mixing In addition spin protected tunneling was observed depending on spin orientation 1 L Fu and C Kane PRL 100 096407 2008 2 N H Lindner E Berg G Refael and A Stern PRX 2 041002 2012 3 D J Clarke J Alicea and K Shtengel Nature Communication 4 1348 2013

Created on 31-05-2017 by Bar Lev, Yevgeny (ybarlev)
Updaded on 31-05-2017 by Bar Lev, Yevgeny (ybarlev)