  The interface between the polar LaAlO$_3$ and nonpolar SrTiO$_3$ layers has
been shown to exhibit various electronic and magnetic phases such as two
dimensional electron gas, superconductivity, magnetism and electronic phase
separation. These rich phases are expected due to the strong interplay between
charge, spin and orbital degree of freedom at the interface between these
complex oxides, leading to the electronic reconstruction in this system.
However, until now all of these new properties have been studied extensively
based on the interfaces which involve a polar LaAlO$_3$ layer. To investigate
the role of the A and B cationic sites of the ABO$_3$ polar layer, here we
study various combinations of polar/nonpolar oxide (NdAlO$_3$/SrTiO$_3$,
PrAlO$_3$/SrTiO$_3$ and NdGaO$_3$/SrTiO$_3$) interfaces which are similar in
nature to LaAlO$_3$/SrTiO$_3$ interface. Our results show that all of these new
interfaces can also produce 2DEG at their interfaces, supporting the idea that
the electronic reconstruction is the driving mechanism for the creation of the
2DEG at these oxide interfaces. Furthermore, the electrical properties of these
interfaces are shown to be strongly governed by the interface strain and strong
correlation effects provided by the polar layers. Our observations may provide
a novel approach to further tune the properties of the 2DEG at the selected
polar/nonpolar oxide interfaces.
