Giant negative magnetoresistance in two-dimensional antidot arrays: ballistic orbital effect and ballistic weak localization

The negative magnetoresistance (MR) in two-dimensional dense antidot arrays has been studied. In order to enhance negative MR, we employed very dense triangular lattices of anisotropic antidots, and realized large negative MR without any oscillatory structures. The negative MR survived even above 100K, and depended on the current direction. So that, the main part of negative MR originates from classical orbital effect. At low temperatures and low magnetic fields, the negative MR have another temperature-sensitive component due to ballistic weak localization. It seems to show no logarithmic behavior.