Résumé:

Single layer back gate graphene filed effect transistors exhibit strong physical magnetoresistance. We measured the maximum magnetoresistance at B=14T within the range R/R=1.5-2, depending on temperature and gate voltage. These values significantly exceed the possible geometrical magnetoresistance estimated for used transistor configuration. The noise measurements at 80 K and 285 K indicated a complex and non-monotonic dependence of 1/f noise on the magnetic field and gate voltage that has never been observed before. In relatively low magnetic fields, B<2 T, the noise decreased with the increasing magnetic field at both temperatures. At high fields B>2 T, the measured spectral noise density increased significantly with increasing magnetic field. The noise amplitude at B=14 T was at least one order of magnitude higher than that at B=0. These dependences cannot be explained by the geometrical effect and, therefore, we conclude that physical (not geometrical) mechanisms are responsible for the observed noise dependence on the magnetic field. Non-monotonic dependence on the magnetic field and a strong increase of noise in high magnetic fields in graphene are very different from what is observed in conventional semiconductors. In particular, GaAs and GaN/AlGaN samples exhibit only a weak dependence of noise on the magnetic field, consistent with the number of carriers fluctuations as the origin of noise in these materials. The reported magnetic field dependence of noise in graphene confirms unconventional nature of noise in graphene.