Topology of Photonic Time Crystals under Complex Refractive Index Modulation

RESUMO

Photonic time crystals, constructed by periodic modulation of electromagnetic parameters in time, hold unique topological properties. Here, we explore permittivity and conductivity co-modulated PTCs (PCM PTCs) by dynamically tuning permittivity and conductivity simultaneously of the spatially-uniform materials, and discover their distinctive non-Hermitian effects. We find that such PCM PTCs hold a global shift of the Floquet spectrum along the imaginary quasifrequency axis, which controls field amplification and decay in both momentum bands and band gaps. By further considering the temporal interface consisting of two different PCM PTCs, we can unveil the relationship between the emergence of topological edge states and momentum band inversion by analyzing the eigenstates at exceptional points. Moreover, the characteristic of the topology of PCM PTCs can also be captured from the complex Dirac mass. Our work studies the topology of PTCs in complex modulation regime, offering new opportunities for manipulating topological edge states in the time domain.