Tunable Superluminal and Subluminal Reflected Group Delay in an Air-Weyl Semimetal Film-Weyl Semimetal Substrate Layered System

In this work, we theoretically investigate the superluminal and subluminal reflected group delay in an air-Weyl semimetal film-Weyl semimetal substrate layered structure by using the
$4\times $
4 transfer matrix method. We show a tunable transition between positive and negative group delays of reflection pulse in this layered structure by controlling the properties of the Weyl Semimetal layer, and we also reveal its mechanism to modify the propagation properties of the light pulse reflected from this structure. It is demonstrated that the reflected group delays are tunable from positive to negative values and vice versa, which are adjusted by tuning the incident angle, thickness of Weyl semimetal film, tilt parameter, and Fermi energy. The control of the magnitude and the sign of the reflected group delay of light propagation represent a key point in slow and fast light technologies. Our results are helpful in controlling pulse propagations and are useful for the design of Weyl semimetal-based delay devices.