Electrostatic modification of novel materials

Abstract

Electric double layer transistor configurations have been employed to electrostatically modify the physical properties of two novel materials; single crystals of insulating strontium titanate (SrTiO₃) and thin films of amorphous indium oxide (a-InO). First the results of doping SrTiO₃ over broad ranges of temperature and carrier concentration employing an ionic liquid as the gate dielectric are reported. The surprising results are, with increasing carrier concentration, an apparent carrier-density dependent conductor-insulator transition, a regime of the anomalous Hall effect, suggesting magnetic ordering, and finally the appearance of superconductivity. The possible appearance of magnetic order near the boundary between the insulating and superconducting regimes is reminiscent of effects associated with quantum critical behavior in some complex compounds. Secondly, the evolution with carrier concentration of the electrical properties of a-InO thin films has been studied. Carrier variations of up to 7 x 10<super>14</super> carriers-cm<super>-2</super> were achieved again using an ionic liquid as a gate dielectric. The superconductor-insulator transition was traversed, and both the magnitude and the position of large magnetoresistance peak found in the insulating regime were modified. The systematic variation of the magnetoresistance peak with charge concentration was found to be qualitatively consistent with a simulation based on a model involving granularity.