  Electronic correlation and reconstruction are two important factors that play
a critical role in shaping the magnetic and electronic properties of correlated
low-dimensional systems. Here, we report a competition between the electronic
correlation and structural reconstruction in La1-xSrxTiO3/SrTiO3
heterostructures by modulating material polarity and interfacial strain,
respectively. The heterostructures exhibit a critical thickness (tc) at which a
metal-to-insulator transition (MIT) abruptly occurs at certain thickness,
accompanied by the coexistence of two- and three-dimensional (2D and 3D)
carriers. Intriguingly, the tc exhibits a V-shaped dependence on the doping
concentration of Sr, with the smallest tc value at x = 0.5. We attribute this
V-shaped dependence to the competition between the electronic reconstruction
(modulated by the polarity) and the electronic correlation (modulated by
strain), which are borne out by the experimental results, including
strain-dependent electronic properties and the evolution of 2D and 3D carriers.
Our findings underscore the significance of the interplay between electronic
reconstruction and correlation in the realization and utilization of emergent
electronic functionalities in low-dimensional correlated systems.
