  Phase competition in correlated oxides offers tantalizing opportunities as
many intriguing physical phenomena occur near the phase transitions. Owing to a
sharp metal-insulator transition (MIT) near room temperature, correlated
vanadium dioxide (VO2) exhibits a strong competition between insulating and
metallic phases that is important for practical applications. However, the
phase boundary undergoes strong modification when strain is involved, yielding
complex phase transitions. Here, we report the emergence of the nanoscale M2
phase domains in VO2 epitaxial films under anisotropic strain relaxation. The
phase states of the films are imaged by multi-length-scale probes, detecting
the structural and electrical properties in individual local domains. Competing
evolution of the M1 and M2 phases indicates a critical role of lattice-strain
on both the stability of the M2 Mott phase and the energetics of the MIT in VO2
films. This study demonstrates how strain engineering can be utilized to design
phase states, which allow deliberate control of MIT behavior at the nanoscale
in epitaxial VO2 films.
