Transport in a modulated one-dimensional ballistic channel

In this paper we review measurements on a modulated one-dimensional (1D) ballistic channel. We have designed a novel 1D channel with three separate and independently contacted overlaying finger gates. By changing the applied voltages on the overlaying gate fingers, we are able to vary the potential modulation in a ballistic 1D channel. Our experimental results fall into two categories, (i) We show that "the 0.7 structure" [K. J. Thomas et al., Phys. Rev. Lett. 77, 135 (1996)] persists despite a change of the lateral confinement strength by a factor of 2. We have also shown that the 0.7 structure present in two 1D channels in series behaves like a single 1D channel, demonstrating that the 0.7 structure is not a transmission effect through a ballistic channel at zero in-plane magnetic field, (ii) In our versatile system, an open quantum dot can be electrostatically defined by a split-gate, and two overlaying finger gates which introduce entrance and exit barriers to the dot. In this case, we observe continuous and periodic oscillations superimposed upon ballistic conductance steps at zero magnetic field. We ascribe the observed conductance oscillations, when the conductance through the dot G exceeds 2e²/h, to experimental evidence for Coulomb charging effects in an open dot [C.-T. Liang et al., Phys. Rev. Lett. 81, 3507 (1998)]. This is supported by the evolution of the oscillatory features for G > 2e²/h as a function of both temperature and barrier transparency. Moreover, we present clear experimental evidence that coherent resonant transport and Coulomb charging effects co-exist in our system.