Spin-induced anomalous magnetoresistance at the (100) surface of   hydrogen-terminated diamond
  We report magnetoresistance measurements of hydrogen-terminated (100)-oriented diamond surfaces where hole carriers are accumulated using an ionic-liquid-gated field-effect-transistor technique. Unexpectedly, the observed magnetoresistance is positive within the range of 2<T<10 K and -7<B<7 T, in striking contrast to the negative magnetoresistance previously detected for similar devices with (111)-oriented diamond surfaces. Furthermore we find: 1) magnetoresistance is orders of magnitude larger than that of the classical orbital magnetoresistance; 2) magnetoresistance is nearly independent of the direction of the applied magnetic field; 3) for the in-plane field, the magnetoresistance ratio defined as [rho(B)-rho(0)]/rho(0) follows a universal function of B/T. These results indicate that the spin degree of freedom of hole carriers plays an important role in the surface conductivity of hydrogen-terminated (100) diamond. 
Yamaguchi Takahide, Yosuke Sasama, Masashi Tanaka, Hiroyuki Takeya,   Yoshihiko Takano, Taisuke Kageura, Hiroshi Kawarada
cond-mat.mes-hall