Quasiparticle doppelgängers

Abstract

Controllable point junctions between different quantum Hall phases are a necessary building block for the development of mesoscopic circuits based on fractionally charged quasiparticles. We demonstrate how particle-hole duality can be exploited to realize such point-contact junctions. We show an implementation for the case of two quantum Hall liquids at filling factors ¼ 1 and à 1 in which both the fractional filling à and the coupling strength can be finely and independently tuned. A peculiar crossover from insulating to conducting behavior as à goes from 1=3 to 1 is observed. These results highlight the key role played on interedge tunneling by local charge depletion at the point contact. DOI: 10.1103/PhysRevLett.103.016802 PACS numbers: 73.43.Jn, 71.10.Pm, 73.21.Hb Fractional quantum Hall (QH) states arise in highquality two-dimensional systems under the influence of quantizing magnetic fields B as a striking consequence of electron-electron interactions [1]. Depending on the fractional value of the filling factor, i.e., the ratio ¼ n=n between the density of charges n and the density of magnetic-flux quanta n ¼ eB=h, the electron system can condense into a variety of strongly correlated quantum liquids characterized by an excitation gap in the bulk and exotic fractionally charged quasiparticles [2]. Thanks to their unique properties, the latter are interesting candidates for novel mesoscopic circuits and QH-based topological qubits [3][4][5][6]. Additionally, several theoretical articles addressed Andreev-like conversion phenomena involving electrons and fractional quasiparticles at the interface between integer and fractional QH phases [7,8]: even device schemes based on these effects were proposed [9]. One crucial building block of these proposals is the point junction between two distinct QH phases. Its experimental realization, however, poses several challenging problems and for this reason the phenomena described above have been largely unexplored so far in experiments.In this Letter we exploit the concept of particle-hole duality [10,11] to realize an integer-to-fractional QH point junctions in which the fractional filling-factor value and the interaction strength can be independently tuned. Tunneling conductance measurements are reported that show an insulating behavior when we couple à ¼ 1=3 QH edges with integer ¼ 1 ones; on the other hand, junctions gradually develop a conducting behavior as à approaches 1. While the insulating behavior is in qualitative agreement with the expected correlation-induced suppression of forward tunneling for fractional edge channels, the observed evolution vs à highlights the peculiar role played by the local filling-factor value determined by depletion in the junction region between the and à regions.The design of our device is based on particle-hole duality [10,11], which is an exact symmetry of the QH system as long as only the first spin-polarized Landau level is occupied and interlevel mixing can be neglected [12]. Duality establishes the occurrence of QH phas...