  Quantum Hall (QH) edge channels appear not only along the edge of the
electron gas but also along an interface between two QH regions with different
filling factors. However, the fundamental transport characteristics of such
interface channels are not well understood, particularly in the high-frequency
regime. In this study, we investigate the interface plasmon mode along the edge
of a metal gate electrode with ungated and gated QH regions in both integer and
fractional QH regimes using a time-resolved measurement scheme. The observed
plasmon waveform was delayed and broadened due to the influence of the charge
puddles formed around the channel. The charge velocity and diffusion constant
of the plasmon mode were evaluated by analyzing the waveform using a
distributed circuit model. We found that the conductive puddles in the gated
region induce significant dissipation in plasmon transport. For instance, a
fractional interface channel with a reasonably fast velocity was obtained by
preparing a fractional state in the ungated region and an integer state in the
gated region, whereas a channel in the swapped configuration was quite
dissipative. This reveals a high-quality interface channel that provides a
clean path to transport fractional charges for studying various fractional QH
phenomena.
