Metal-to-insulator transition in Ruddlesden-Popper-type Sr_n+1V_nO_3n+1 (n = 1, 2) epitaxial thin films as a function of strain and VO₂ stacking layer number

A series of Ruddlesden-Popper-type Sr_n+1V_nO_3n+1 (n = 1, 2) (001) epitaxial thin films was grown on LaAlO₃ and LaSrGaO₄ substrates with tensile and compressive epitaxial strains, respectively. The decrease in VO₂ stacking layer number n and the increase in the interlayer distance between the (VO₂)_n layers resulted in metal-to-insulator transition. The sheet conductance of a single (VO₂)_n layer in Sr_n+1V_nO_3n+1 (n = 1, 2) was close to the well-known Ioffe-Regel limit, which suggests their two-dimensional electrical conduction. From resistivity and magnetoconductance measurements, it is found that renormalized electron-electron interaction and/or the Kondo effect were enhanced with the decrease in n, and possible quantum interference effects like weak localization were induced with the increase in the interlayer distance.