Electrostatic modulation of anisotropic magnetotransport in Ar+-irradiated SrTiO3: Effects of boundary scattering

We present low temperature, magnetotransport measurements on a quasi-two-dimensional electron gas created by Ar+-irradiation of SrTiO3. We observe negative (positive) magnetoresistance for fields applied in (out of) the plane of the electron gas. By modulating the mobility mu of the electron gas through an electrostatic field, we find the in-plane magnetoresistance is a function of the cyclotron frequency. The negative in-plane magnetoresistance can be explained by a drop in boundary scattering, which occurs as the cyclotron orbits become smaller than the finite thickness of the electron gas. These results elucidate the critical role boundary scattering plays in the magnetotransport of quasi-two-dimensional electron gases. The implications of these results on recent magnetotransport measurements of LaAlO3/SrTiO3 samples are discussed.