Magnetic anisotropy of single Mn acceptors in GaAs in an external magnetic field

We investigate the effect of an external magnetic field on the physical properties of the acceptor hole states associated with single Mn acceptors placed near the (110) surface of GaAs. Cross-sectional scanning tunneling microscopy images of the acceptor local density of states (LDOS) show that the strongly anisotropic hole wave function is not significantly affected by a magnetic field up to 6 T. These experimental results are supported by theoretical calculations based on a tight-binding model of Mn acceptors in GaAs. For Mn acceptors on the (110) surface and the subsurfaces immediately underneath, we find that an applied magnetic field modifies significantly the magnetic anisotropy landscape. However, the acceptor hole wave function is strongly localized around the Mn and the LDOS is quite independent of the direction of the Mn magnetic moment. On the other hand, for Mn acceptors placed on deeper layers below the surface, the acceptor hole wave function is more delocalized and the corresponding LDOS is much more sensitive on the direction of the Mn magnetic moment. However, the magnetic anisotropy energy for these magnetic impurities is large (up to 15 meV), and a magnetic field of 10 T can hardly change the landscape and rotate the direction of the Mn magnetic moment away from its easy axis. We predict that substantially larger magnetic fields are required to observe a significant field dependence of the tunneling current for impurities located several layers below the GaAs surface