Fig. 1

Schematic of quadratic band touchings in a system that is slightly doped to give a finite E F. One can distinguish the contribution of low-energy Drude excitations near E F as well as virtual and real interband transitions

Schematic of quadratic band touchings in a system that is slightly doped to give a finite E F. One can distinguish the contribution of low-energy Drude excitations near E F as well as virtual and real interband transitions