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Abstract

An experimental analysis of the negative magnetoresistance due
to weak localization in a dense hexagonal lattice of antidots
created from a two-dimensional electron gas formed at an
AlGaAs/GaAs heterojunction is presented. The low-field
magnetoresistance is perfectly described by the conventional
theory for disordered conductors, using the phase coherence
length l(phi) and a B-independent prefactor alpha as adjustable
parameters. An unusual T-1/4 dependence is found for l(phi),
which is in contradiction to the predictions of' most of' the
models proposed for phase breaking processes. A saturation of
l(phi) is observed below 600 mK. Surprisingly, alpha, which
determines the amplitude of the weak localization correction to
the conductivity. exhibits high values ( 1.5<α<6), and a
behavior that cannot be explained by current theories of weak
localization in disordered Conductors nor in ballistic systems.
We explain semiclassically our results in terms of' electrons
trapped in the unit cells formed by the neighboring antidots,
such that the length of the interfering paths is limited by the
geometry of the cell. In this case. the weak localization and
negative magnetoresistance are more likely to be determined by
a specific dimension of the system rather than any decoherence
process.