Magnetoconductance of independently tunable tunnel-coupled double quantum wires

We report on our recent experimental studies of vertically coupled quantum point contacts subject to in-plane magnetic fields. Using a novel flip-chip technique, mutually aligned split gates on both sides of sub-micron thick double quantum well heterostructure define a closely coupled pair of ballistic one-dimensional (1D) constrictions. We observe quantized conductance steps due to each quantum well and demonstrate independent control of each 1D constriction width. In addition, a novel magnetoconductance feature at similar to 6 T is observed when a magnetic field is applied perpendicular to both the current and growth directions. This conductance dip is observed only when 1D subbands are populated in both the top and bottom constrictions. This data is consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of 1D subbands. (C) 2000 Elsevier Science B.V. All rights reserved.