Dual-band flexible THz metamirror for spin-selective flips

Metasurfaces with in-plane structure asymmetry have been widely investigated for realizing chiral characteristics which rarely exist in natural materials. The chiral metamirror, a novel metasurface, responds differently to the handedness of the designed circularly polarized waves. However, previously reported chiral metamirrors are limited to reflecting the circularly polarized waves with fixed polarization in a narrow band, severely restricting their potential engineering applications. Herein, we have experimentally demonstrated a dual-band spin-selection flips THz chiral metamirror with huge circular dichroism (CD) by constructing the asymmetry unit cells. Notably, the proposed chiral metamirror enables the realization of the flips of the spin-selective reflected waves in the two operating bands. Moreover, the circular polarization selection efficiency (CPSE) can be controlled flexibly, as well as the strong CD, by adjusting the configuration of the unit cells. Even more important, the distribution of the currents in the two arms of the unit cell with different bands has revealed the inner mechanism of chirality. Furthermore, compared with other traditional devices, we have fabricated the flexible metadevice for facilitating integration by introducing the modified polyimide (MPI). The results show that the chiral characteristic of spin-selective reflected waves can be completely controlled by precisely designing the unit cells of chiral metamirror, which has shown a great application prospect in many fields, such as electronic devices and bio-sensors.