Metal-insulator transitions in strained single quantum wells of ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_{x}V{O}_3$

Metal-insulator transitions (MITs) are ubiquitous in strongly correlated electron systems. However, there is an unexplored area of study: the artificially confined systems of strained quantum wells that are comprehensively studied in semiconductors for practical device applications. Here we have systematically studied quantum wells of ${\mathrm{Sr}}_{1–x}{\mathrm{La}}_{x}V{O}_3$, a compound that evolves from a $3d^1$ metal ($\mathrm{SrV}{O}_3$) to a $3d^2$ Mott insulator ($\mathrm{LaV}{O}_3$). The two-dimensional confinement is shown to enhance the stability of the insulating phase, shifting the critical MIT value of $x$ from $x=0$.82 for the bulk to around $x=0.50$ at a thickness of 4 unit cells (u.c.); below 3 u.c. the insulating state merges with the newly emerging $d^1$ Mott insulator state ($x=0$). The Mott insulator states are further stabilized by a tensile epitaxial strain, presumably due to the enhanced correlation in selectively occupied $d_{xy}$ orbitals. These findings pave the way for exploring Mott physics in an artificially confined system of a strongly correlated electron system.