Giant anisotropic magnetoresistance in insulating ultrathin (Ga,Mn)As
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Molecular-beam epitaxy grown, 5 nm thick annealed Ga0.95Mn0.05As films demonstrate transition from metallic to insulating state for sheet resistances near resistance quantum, which we connect with the two-dimensional hole localization. Below the metal-insulator transition we found the giant anisotropic magnetoresistance (GAMR) effect, which depends on the orientation of magnetization to crystallographic axes and demonstrates the twofold symmetry angular dependence. The GAMR manifests itself in positive magnetoresistance near 50% at T=1.7 K for H// crystallographic direction in contrast to smaller negative magnetoresistance for H// direction. We connect the GAMR with formation of high- and low-resistance states with different localization due to anisotropic spin-orbit interaction.