Topological defects in the edge-state structure in a bilayer electron system

Abstract

We experimentally demonstrate, for the first time, formation of point-like topological defects in the edge state structure in the quantum Hall effect regime. By using of a selective population technique, we investigate equilibration processes between the edge states in bilayer electron structures with a high tunnelling rate between layers. Unexpected flattening of the I − V curves in perpendicular magnetic field at a specific filling factor combination and the recovery of the conventional nonlinear I − V characteristics in tilted fields give a strong evidence for the existence of topological defects.

Transport Properties in Bilayer Quantum Hall Systems in the Presence of a Topological Defect

“…Such a picture can be destroyed by an in-plane magnetic field component which washes out the above crossing; the I − V curves become then strongly non-linear so signaling the merging of a tunneling process. All the above features in the I − V characteristics appear to be the fingerprints of the presence of a topological defect induced by the different pseudospin configurations in bilayer quantum Hall systems [2].…”

“…More interesting features take place in the transport properties of bilayer systems when also pseudospin (related to the layer index) is involved [6] [9]. Recently the presence of edge state crossings and thus of topological defects has been experimentally evidenced in such systems in a quasi-Corbino geometry [10] at filling ν = 3 [2] by means of a selective population technique. In particular the application of a suitable gate voltage V g and of a magnetic field drives the bilayer in different pseudospin states in the gated and ungated regions, so producing a crossing of the edge states which has been detected in the transport properties.…”

Separately contacted edge states at high imbalance in the integer and fractional quantum Hall effect regime

“…The existence of a gate in this geometry, in particular, allows changing the symmetry of the quantum well, and hence the energy spectrum under the gate [21,22]. Since the structure of edge states corresponds to the structure of the bulk spectrum [27], the quasi-Corbino geometry allows to realize topological defects in the structure of edge states [30]: (i) If the well is asymmetric in the interaction area of the edge states, then edge-state electrons are fully described by the spin and isospin (layer number) orientations [21]. Electrons injected from beneath the gate can also come either from an isospin-polarized state or from a mixed one.…”

A conformal field theory description of magnetic flux fractionalization in Josephson junction ladders

“…It is interesting to notice that the presence of a topological defect has been experimentally evidenced very recently for a two layers quantum Hall system, by measuring the conduction properties between two edge states of the system [21].…”