Modulation of the low-temperature magnetoresistance of Ar-irradiated SrTiO$_3$ via field-effect gate doping

Recent experiments have shown that irradiating single crystal SrTiO$_3$ with Ar ions can create an amorphous surface layer with a quasi-2-dimensional electron gas (Q2DEG) below. We present low-temperature magnetotransport measurements of this Q2DEG system, as a function of gate doping. The magnetoresistance can be tuned as n-type carriers are doped into the interface between the amorphous and crystalline SrTiO$_3$ layers. Anisotropy in the magnetoresistance is also measured with respect to the direction of the applied magnetic field. These results will be compared with the magnetotransport properties of LaAlO$_3$/ SrTiO$_3$ heterostructures, where the possibility of novel magnetic behavior will be discussed.