Probing phase transition in VO with the novel observation of low-frequency collective spin excitation.

VO is well known for its first order, reversible, metal-to-insulator transition (MIT) along with a simultaneous structural phase transition (SPT) from a high-temperature metallic rutile tetragonal (R) to an insulating low-temperature monoclinic (M1) phase via two other insulating metastable phases of monoclinic M2 and triclinic T. At the same time, VO gains tremendous attention because of the half-a-century-old controversy over its origin, whether electron-electron correlation or electron-phonon coupling trigger the phase transition. In this regard, VMgO samples were grown in stable phases of VO (M1, M2, and T) by controlled doping of Mg.

The role of 1-D finite size Heisenberg chains in increasing the metal to insulator transition temperature in hole rich VO.

VO samples are grown with different oxygen concentrations leading to different monoclinic, M1, and triclinic, T, insulating phases which undergo a first order metal to insulator transition (MIT) followed by a structural phase transition (SPT) to the rutile tetragonal phase. The metal insulator transition temperature (T) was found to be increased with increasing native defects. Vanadium vacancy (V) is envisaged to create local strains in the lattice which prevents twisting of the V-V dimers promoting metastable monoclinic, M2 and T phases at intermediate temperatures.