  In this paper, the reflected group delay from a multilayer structure where
Dirac semimetal is coated on one-dimensional photonic crystal (1D PC) separated
by a spacer layer is investigated theoretically. It is shown that the group
delayof reflected beam in this structure can be significant enhanced negatively
and can be switched from negative to positive. The enhanced group delay
originates from the steep phase change caused by the excitation of Tamm
plasmons at the interface between the Dirac semimetal and spacer layer. It is
clear that the positive and negative group delay can be actively tuned through
the Fermi energy and the relaxation time of the Dirac semimetal. We believe
this enhanced and tunable delay scheme is promising for fabricating optical
delay devices and other applications at middle infrared band.
