arXiv subjects

Chenwen Yang

Publications and source records attributed to Chenwen Yang.

5 recordsLinked to original sources

arXiv2026

Dynamic Chirality in Photonic Time Crystals

Temporal modulation offers a fundamentally distinct degree of freedom for active wave control beyond static spatial structuring. Photonic time crystals (PTCs), based on periodic modulation of electromagnetic parameters in time, have expanded photonic band engineering from space to time by enabling controlled energy exchange between light and the modulation. Yet, the use of PTCs to synthesize rotational dynamics and thereby control chirality and circular dichroism (CD) remains largely unexplored. Here, we propose a spatiotemporal PTC whose central cylindrical element is driven by an azimuthally traveling-wave permittivity modulation. Although the structure is geometrically static, its dielectric profile evolves as an effectively rotating pattern in time. This synthetic rotation lifts a static modal degeneracy and produces two nondegenerate counter-rotating states with opposite orbital angular momenta. These chiral modes selectively couple to left- and right-circularly polarized light, giving rise to tunable CD. In addition, the spatiotemporal modulation induces orbital angular-momentum conversion between the Floquet replica bands. Our work reveals the microscopic origin of dynamic chiral response and establishes a strategy for reconfigurable chiral photonics without mechanical motion.

physics.optics↗

arXiv2026

Chiral switching of elastic spin via dynamic encirclement of exceptional points

Dynamically encircling exceptional points (EPs) enables chiral state conversion in classical wave systems. However, whether this mechanism can be extended to chiral spin conversion has remained elusive. Here we demonstrate chiral switching of elastic spin via dynamic encirclement of EPs in a non-Hermitian micropolar (Cosserat) metamaterial. The interplay between micropolar chirality and anisotropic loss generates EPs with a nontrivial Riemann-sheet topology. Encircling these EPs converts the elastic spin, with the final spin sign dictated solely by the handedness of the encircling trajectory. Our results establish a fundamental route for the selective manipulation of elastic spin, opening avenues for non-Hermitian spin phononics and broader applications in other wave systems.

physics.class-ph↗

arXiv2023

Hybrid Spin and Anomalous Spin-Momentum Locking in Surface Elastic Waves

Transverse spin of surface waves is a universal phenomenon which has recently attracted significant attention in optics and acoustics. It appears in gravity water waves, surface plasmon-polaritons, surface acoustic waves, and exhibits remarkable intrinsic spin-momentum locking, which has found useful applications for efficient spin-direction couplers. Here we demonstrate, both theoretically and experimentally, that the transverse spin of surface elastic (Rayleigh) waves has an anomalous sign near the surface, opposite to that in the case of electromagnetic, sound, or water surface waves. This anomalous sign appears due to the hybrid (neither transverse nor longitudinal) nature of elastic surface waves. Furthermore, we show that this sign anomaly can be employed for the selective spin-controlled excitation of symmetric and antisymmetric Lamb modes propagating in opposite directions in an elastic plate. Our results pave the way for spin-controlled manipulation of elastic waves and can be important for a variety of areas, from phononic spin-based devices to seismic waves.

physics.app-ph↗

arXiv2022

Universal Relations of Energy Flow, Acoustic Spin and Torque for Near-Field Acoustic Tweezers

Acoustic spin, radiation torque, energy flow, and reactive power are of significant importance from both fundamental and practical aspects, responsible for flexible tweezer manipulations and near-field sound directionality. Nevertheless, the intrinsic relations among these physical quantities are far from clear. Here, we prove the universal geometric relations among them in acoustics, independent on wave structure details. Particularly, we connect acoustic spin and torque to the cross product of time-averaged energy flow and reactive power, as well as to the local vorticity of energy flow. These relations are universally valid, verified in a variety of different acoustic systems. We also demonstrate the multipole mechanical torques and forces generated in three acoustic near-field sources: Janus, Huygens and Spin sources, applying on small lossy particles. These universal geometric relations uncover hidden locking relations beyond simple spin-momentum locking of near-field waves, and show the basic principles between the acoustic spin, radiation torque, and energy flow, reactive power.

cond-mat.other↗

arXiv2022

Elastic Valley Spin Controlled Chiral Coupling in Topological Valley Phononic Crystals

Distinct from the phononic valley pseudo-spin, the real physical spin of elastic waves adds a novel tool-kit capable of envisaging the valley-spin physics of topological valley phononic crystals from a local viewpoint. Here, we report the observation of local elastic valley spin as well as the hidden elastic spin-valley locking mechanism overlooked before. We demonstrate that the selective one-way routing of valley phonon states along the topological interface can be reversed by imposing the elastic spin meta-source at different interface locations with opposite valley-spin correspondence. We unveil the physical mechanism of selective directionality as the elastic spin controlled chiral coupling of valley phonon states, through both analytical theory and experimental measurement of the opposite local elastic spin density at different interface locations for different transport directions. The elastic spin of valley topological edge phonons can be extended to other topological states and offers new tool to explore topological metamaterials.

cond-mat.mes-hall↗