Fundamental relation between phase and group velocity, and application to the failure of perfectly matched layers in backward-wave structures
Loh, Po-Ru, Ardavan Oskooi, Mihai Ibanescu, Maksim Skorobogatiy, and Steven Johnson. 2009. “Fundamental Relation Between Phase and Group Velocity, and Application to the Failure of Perfectly Matched Layers in Backward-Wave Structures”. Phys Rev E Stat Nonlin Soft Matter Phys 79 (6 Pt 2): 065601.