Active Optical Metasurfaces Based on Defect-Engineered Phase-Transition Materials, J. Rensberg, S. Zhang, Y. Zhou, A. S. McLeod, C. Schwarz, M. Goldflam, M. Liu, J. Kerbusch, R. Nawrodt, S. Ramanathan, D. N. Basov, F. Capasso, C. Ronning and M. A. Kats, Nano Letters, 16, 1050 (2016)