STUDY OF NOVEL QUANTUM PHENOMENA OBSERVED AT OXIDES INTERFACES

Abstract

In condensed matter physics the quasi two-dimensional electron gas at the interface of two different insulators, polar LaAlO&#8323 on non-polar SrTiO&#8323 (LaAlO&#8323/SrTiO&#8323) is a spectacular and surprising observation. This phenomenon is LaAlO&#8323 film thickness-dependent and may be explained by the polarization catastrophe model, in which a charge transfer of 0.5e&#8315 from the LaAlO&#8323 film into the LaAlO&#8323/SrTiO&#8323 interface is expected. Here we show that in conducting samples (&#8805 4 unit cells of LaAlO&#8323) there is indeed a ~0.5e&#8315 transfer from LaAlO&#8323 into the LaAlO&#8323/SrTiO&#8323 interface by studying the optical conductivity in a broad energy range (0.5¿35 eV). Surprisingly, in insulating samples (&#8804 3 unit cells of LaAlO&#8323) a redistribution of charges within the polar LaAlO&#8323 sub-layers (from AlO&#8322 to LaO) as large as ~0.5e&#8315 is observed, with no charge transfer into the interface. Hence, our results reveal the different mechanisms for the polarization catastrophe compensation in insulating and conducting LaAlO&#8323/SrTiO&#8323 interfaces.