Pure electronic control of metal-insulator transition in VO₂

The strong electronic correlation in d-orbitals enforces VO₂ to undergo a metal-to-insulator transition (MIT) at T_MIT (~341 K). The control of T_MIT by carrier doping or modifying strain is a well-known technique that enhances the applicability of VO₂ and offers a platform for a better understanding of MIT. However, it is hard to control MIT without affecting any changes to the lattice. For example, the control of MIT in VO₂ by elemental doping, strain, or oxygen vacancy creation all affect the lattice parameters of VO₂. In this work, we present VO₂-based modulation-doped heterostructures to control the MIT in VO₂. Atomically sharp and coherently strained single-crystalline VO₂ (001) heterostructures were grown with VO₂ thicknesses from 1.5 nm to 9.5 nm which result in a coherent reduction of T_MIT by ~65 K. Using Hall measurements, we show that the reduction in MIT corresponds to an increase in electron densities without any measurable changes in the lattice parameter (C_R). HAXPES spectra of V_2p and V_3d further confirm the existence of interfacial band bending of VO₂ due to carrier doping. We show that the MIT in VO₂ is robust even in the presence of carrier densities as high as 9x10²¹ cm^-3. Our studies open the possibility of studying MITs in correlated electron materials under pure electronic control.