Electronic correlations are crucial in 2DEG based on STO

I have highlighted a number of studies on the 2DEG that were created about the interfaces based on SrTiO3 compounds. The 2DEG thus obtained have been shown with various interesting ground states including superconducting ones. Here comes a new work [Science, 331 (6019): 886-889] that demonstrates the importance of electronic correlations in determining the transport properties of this 2DEG. This time the 2DEG was introduced by inserting a RO layer, R=La, Pr,Nd,Sm and Y, in the SrTiO3 matrix. It turns out that, the electronic properties of this 2DEG are crucially hinging on the R element. For La, Pr and Nd, it is conducting while for the rest it is insulating.

The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO₃) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local spectroscopic and theoretical results indicate that the interfacial conductivity is dependent on electronic correlations that decay spatially into the SrTiO₃ matrix. Such correlation effects can lead to new functionalities in designed heterostructures.