Vanadium dioxide (VO2) has posed many lingering questions about the origin of its characteristic insulator to metal transition (IMT). VO2 is known to undergo first order IMT around the transition temperature 340 K, accompanied by the structural transition from the rutile (R) metallic to the insulating monoclinic (M1) phase. The nature of the IMT in VO2 has remained controversial whether Peierls assisted or correlation driven involving electron-lattice and electron-electron interactions, respectively. VO2 exhibits several insulating phases (monoclinic M1, M2, and triclinic T), and the study of these phases is important for understanding the true nature of the IMT in VO2. These insulating phases have small but discernible crystallographic differences in the vanadium chains forming the dimers.

We have studied structural, electrical, ultrafast-reflectivity, and electronic structure properties of the T-phase Cr-doped VO2 and the M1-phase pure VO2 thin films, both grown by pulsed laser deposition under identical conditions. An intermediate M2 structure is observed in the Cr-doped VO2, while the pure VO2 directly goes from the insulating monoclinic M1 structure to a metallic rutile R structure, manifested by temperature-dependent Raman spectroscopy.

The IMT in VO2 is accompanied by a transition from infrared (IR) transparent (insulating phase) to IR opaque (metallic phase). A decrease in the IR transmittance of the VO2 with an increase in the temperature is directly associated with the vanishing of the VO2 insulating band gap. Bandgap in VO2 mainly arises due to the V-V dimerization and the strong electron correlations present within the V-V dimers. Transition in IR transmittance makes VO2 a potential candidate for the manufacturing of energy-saving smart thermochromic windows. Tailoring of the IMT and associated optical properties was made possible via electron-doped (W) and hole-doped (Tb) atoms.

Dr. Suhail Majid is currently working as a Postdoc Fellow at the Department of Physics, KFUPM, Saudi Arabia. He did his Ph.D. from Aligarh Muslim University in joint collaboration with UGC-DAE CSR, Indore, India. He has studied the electronic structure of novel oxide-based thin films using synchrotron sources at RRCAT and DSEY, Germany, and conducted postdoctoral research at Academia Sinica, Taiwan, where he worked in the area of high-pressure ultrafast Physics to explore the dynamics of materials at high pressure and on an ultrafast timescale.

Dr. Suhail has worked in the field of experimental condensed matter physics, studied novel materials meant for both physics understanding and technological applications. He has worked on various transport, optical, and spectroscopic techniques during his research tenure.

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