Dynamic control of topological phase of Dirac semimetallic terahertz metasurface

With the rapid advancement of terahertz technology, multifunctional coding metasurfaces have emerged as a significant research frontier in this domain. However, the rigid geometric structure of traditional metasurfaces poses challenges in accommodating both multifunctionality and dynamic control requirements. This study proposes an adjustable exceptional topological phase coding metasurface device based on Dirac semimetal (DSM). By optimizing the structural parameters to excite multiple exceptional points (EP), the unique topological phase distribution facilitates multi-dimensional control of terahertz waves. The findings demonstrate that, under the incidence of left-handed circularly polarized (LCP) light, the metasurface device can stably generate vortex light with a topological charge of l = 1. In the left- and right-handed circularly polarized channels, the wavefronts of the vortex beam and the split beam are independently controlled, along with digital '0' and '5' dual-channel holographic imaging. The near-field grayscale imaging of the 'little grey dog' image is achieved by utilizing the differentiated absorption characteristics of the EP to LCP. Furthermore, by dynamically adjusting the Fermi level of the DSM, reversible switching of the reflection mode state is accomplished under the same incident conditions. This research provides a theoretical and practical foundation for enhancing the capacity of terahertz communication systems and optimizing terahertz near-field and far-field imaging technologies. It holds significant scientific value and application prospects for advancing the development of independently adjustable multifunctional devices.