Ballistic transport in quantum channels modulated with double-bend structures

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Abstract
We report on quantum-mechanical calculations of ballistic transport in finite quantum channels with single and multiple double-bend discontinuities. The channels connect to two semi-infinite two-dimensional electron gases, which serve as emitter and collector when a potential difference is applied. The calculations are performed by use of a transfer-matrix method formulated by using one common basis for all matrices required for the description of the electron states in the finite channel. It is shown that in the quantum channel with a single double-bend discontinuity, at least one conductance peak can be found at an energy below the threshold of the first plateau. These peaks appear due to resonant tunneling via quasibound states at energies below the first transverse mode. It is also shown that in the quantum channel with a multiple double-bend discontinuity the quasibound states in different double-bend regions couple to each other, leading to multiple splits of the conductance peaks. Critical discussions on recent experimental measurements and theoretical calculations on electron transport in doubly bent quantum channels are presented. We emphasize the fact that the quasibound states can be probed by electron transmissions only if the doubly bent channel is of finite length, and only if we also consider the electron states in much wider outside regions connected with the channel.