Intrinsic Electronic Confinement at Conducting Oxide Interfaces

The discovery of a two-dimensional electron liquid (2DEL), confined at the interface between the two band insulators LaAlO$_{\mathrm{3}}$ (LAO) and SrTiO$_{\mathrm{3}}$ (STO) has generated tremendous research interest [1]. The 2DEL confinement lifts the degeneracy of Ti t$_{\mathrm{2g}}$ orbitals and promotes exotic physical properties [2]. A previous study [3] has demonstrated that a 2DEL is also observed when LAO is alloyed with STO (La,Al)$_{\mathrm{1-}}_{x}$(Sr,Ti)$_{x}$O$_{\mathrm{3}}$ (LASTO:$x)$. The threshold thickness required for the onset of conductivity scales with $x$. We present here a study of magnetotransport and superconductivity at the (LASTO:0.5)/STO interface. The thickness of the 2DEL, measured using perpendicular and parallel critical fields is larger than the one at the LAO/STO interface. This change is due to a modification on the confining potential linked to a reduced charge transfer that is scaling as 1/x. This study supports an intrinsic origin to the formation of the 2DEL in the LAO/STO system. [1] A. Ohtomo, H. Y. Hwang, Nature \textbf{427}, 423 (2004). [2] P. Zubko, S. Gariglio, M. Gabay, P. Ghosez, and J.-M. Triscone, Annual Review of Condensed Matter Physics \textbf{2}, 141 (2011). [3] M.L. Reinle-Schmitt, C. Cancellieri, D. Li, D. Fontaine, M. Medarde, E. Pomjakushina, C.W. Schneider, S. Gariglio, P. Ghosez, J.-M. Triscone, and P.R. Willmott, Nature Communications \textbf{3}, 932 (2012).