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1. Characterization of VO2 Reconfigurable Linear-to-Circular Polarization Converter

   https://doi.org/10.1109/USNC-URSI52151.2023.10238101  

   West, David; Lust, Mark; Ghalichechian, Nima (July 2023, IEEE)
2. Tuning of Optical Phonons in α-MoO3–VO2 Multilayers

   https://doi.org/doi.org/10.1021/acsami.1c12320  

   Dereshgi, Sina; Larciprete, Maria; Centini, Marco; Murthy, Akshay; Tang, Kechao; Wu, Junqiao; Dravid, Vinayak; Aydin, Koray (October 2021, ACS applied materials interfaces)

   Merging the properties of VO2 and van der Waals (vdW) materials has given rise to novel tunable photonic devices. Despite recent studies on the effect of the phase change of VO2 on tuning near-field optical response of phonon polaritons in the infrared range, active tuning of optical phonons (OPhs) using far-field techniques has been scarce. Here, we investigate the tunability of OPhs of α-MoO3 in a multilayer structure with VO2. Our experiments show the frequency and intensity tuning of 2 cm–1 and 11% for OPhs in the [100] direction and 2 cm–1 and 28% for OPhs in the [010] crystal direction of α-MoO3. Using the effective medium theory and dielectric models of each layer, we verify these findings with simulations. We then use loss tangent analysis and remove the effect of the substrate to understand the origin of these spectral characteristics. We expect that these findings will assist in intelligently designing tunable photonic devices for infrared applications, such as tunable camouflage and radiative cooling devices. 

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3. Reliability of VO2-Based mmWave Switches Under 100 Million Thermal Cycles

   https://doi.org/10.1109/TDMR.2023.3249771  

   Chen, Shangyi; Lust, Mark; Roo, Annie; Ghalichechian, Nima (June 2023, IEEE Transactions on Device and Materials Reliability)
4. Effects of charge fluctuation and charge regulation on the phase transitions in stoichiometric VO2

   https://doi.org/10.1038/s41598-020-73447-9  

   Joshi, Siddharth; Smieszek, Nicholas; Chakrapani, Vidhya (October 2020, Scientific Reports)

   Abstract Detailed electrical and photoemission studies were carried out to probe the chemical nature of the insulating ground state of VO₂, whose properties have been an issue for accurate prediction by common theoretical probes. The effects of a systematic modulation of oxygen over-stoichiometry of VO₂from 1.86 to 2.44 on the band structure and insulator–metal transitions are presented for the first time. Results offer a different perspective on the temperature- and doping-induced IMT process. They suggest that charge fluctuation in the metallic phase of intrinsic VO₂results in the formation of e⁻and h⁺pairs that lead to delocalized polaronic V³⁺and V⁵⁺cation states. The metal-to-insulator transition is linked to the cooperative effects of changes in the V–O bond length, localization of V³⁺electrons at V⁵⁺sites, which results in the formation of V⁴⁺–V⁴⁺dimers, and removal of$$\pi^{*}$$ ${\pi }^{\ast }$screening electrons. It is shown that the nature of phase transitions is linked to the lattice V³⁺/V⁵⁺concentrations of stoichiometric VO₂and that electronic transitions are regulated by the interplay between charge fluctuation, charge redistribution, and structural transition. 

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5. Probing the Critical Nucleus Size in the Metal-Insulator Phase Transition of VO2

   https://doi.org/10.1103/PhysRevLett.129.245701  

   Jin, Lei; Shi, Yin; Allen, Frances I.; Chen, Long-Qing; Wu, Junqiao (December 2022, Physical Review Letters)