Quasilinear magnetoresistance in an almost two-dimensional band structure

We present a theoretical study of the orbital magnetoresistance in a unixial anisotropic metal within the relaxation-time approximation. The appearance of a new dimensionless scale, delta=4t_perp/epsilon_F, allows the possibility of a new region at intermediate fields where the magnetoresistance is linear in applied magnetic field for currents flowing along the unixial direction. (Here, t_perp characterizes the bandwidth along the unixial direction.) In the limit of large anisotropy (small delta), corresponding to a quasi-two-dimensional metal made up of weakly coupled layers, we obtain an analytic expression for the magnetoresistance valid for all magnetic fields. We test our analytic results numerically and we compare our expressions with the c-axis magnetoresistance of Sr_2RuO_4.