Giant negative magnetoresistance in semiconductors doped by multiply   charged deep impurities
  A giant negative magnetoresistance has been observed in bulk germanium doped with multiply charged deep impurities. Applying a magnetic field the resistance may decrease exponentially at any orientation of the field. A drop of the resistance as much as about 10000% has been measured at 6 T. The effect is attributed to the spin splitting of impurity ground state with a very large g-factor in the order of several tens depending on impurity. 
S.D. Ganichev, H. Ketterl, W. Prettl, I.A. Merkulov, V.I. Perel, I.N.   Yassievich, A.V. Malyshev