  A shoulder-like feature close to $(0.7\times 2e^{2}/h)$, "the 0.7 structure"
at zero magnetic field was observed in clean one-dimensional (1D) channels
[K.J. Thomas et al., Phys. Rev. Lett. 77, 135 (1996)]. To provide further
understanding of this structure, we have performed low-temperature measurements
of a novel design of 1D channel with overlaying finger gates to study the 0.7
structure as a function of lateral confinement strength and potential profile.
We found that the structure persists when the lateral confinement strength is
changed 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 which shows the 0.7
structure, demonstrating that the 0.7 structure is not a transmission effect
through a ballistic channel at zero in-plane magnetic field.
