Magnetoresistance and hall effect of two-dimensional 2H-NbSe2

Single crystals of two-dimensional 2H-NbSe2, which undergo superconducting transition at T-C=7.1K and charge-density wave (CDW) transition at T-CDW=30K, were synthesized. The resistance residual ratio (RRR=R(300K)/R(8K)) of the samples from different batches varies from 10 to 30, but the superconducting properties hardly change with RRR. The magneto-resistance (MR)is generally small and its temperature and field dependence of MR violate the Kohler's rule that holds for many conventional metals, indicating that the scattering times of charge carriers are no longer isotropic. The steep decrease of Hall coefficient R-H below 50K can be interpreted by the drastic increase of the mean-free-path of electron type charge carrier. The influence of CD W transition on the resistivity and Hall effect is discussed in a two-band model.