arXiv subjects

Chunqi Zheng

Publications and source records attributed to Chunqi Zheng.

5 recordsLinked to original sources

arXiv2026

Probing mesoscopic nonlocal screening in van der Waals heterostructures with polaritons

Predictive optical modelling of van der Waals (vdW) heterostructures is critical for meta-optics, near-field photonics and quantum technologies. At their buried interfaces, charge transfer and spatially extended screening challenge local descriptions based on layer-by-layer stacking of fixed permittivity tensors. However, such nonlocal corrections have been established mainly for plasmonic systems at ångström-nanometre scales and are often assumed negligible on optical-wavelength scales. Here we challenge this view by uncovering a mesoscopic nonlocal screening regime, extending up to ~140 nm, at buried charge-transfer interfaces in transition-metal dichalcogenide/α-molybdenum trioxide (TMDC/α-MoO3) phonon-polaritonic heterostructures. Using phonon polaritons as an ultrasensitive probe, we quantify charge transfer from polariton-wavelength shifts and find a thickness-independent saturated response as α-MoO3 is thinned. Rather than merely complicating optical modelling, this nonlocal saturation turns a design-level correction into an opportunity by yielding a transferable cross-material metric. Across more than 120 devices, this metric scales linearly with the work-function difference between the TMDC and α-MoO3. We further identify a lattice-mismatch-set energy threshold for charge transfer, revising Anderson-type band alignment for vdW interfaces.

physics.optics↗

arXiv2026

Canalized hyperbolic magnetoexciton polaritons enabled by the Shubnikov-de Haas effect in van der Waals semiconductors

Polariton canalization exhibits highly collimated and diffraction-free propagation characteristics in natural hyperbolic materials, holding great promise for molding the energy flow at nanoscale. Previously, the majority of canalizations are realized in phonon polaritons. Herein, we theoretically explore hyperbolic magnetoexciton polaritons (HMEPs) in van der Waals crystals of WTe2, MoS2, and phosphorene. Based on the Shubnikov-de Haas effect, canalized HMEPs with ultralow group velocity (~10-5c) and super-long lifetime (hundreds of microseconds) are predicted at low temperatures. We also show that the inter-Landau-level transitions and non-local dielectric screening effect significantly modify the optical topologies of canalized HMEPs, manifested by various exotic isofrequency contours (IFCs) including hyperbolic, witch-of-Agnesi, one-sheet, two-fold, and twisted pincerlike IFCs. Our findings reveal the significant effects of magneto-optical transport on hyperbolic polaritons, which not only enrich the interplay mechanism between magnetics and polaritonics, but also provide a promising playground for future developments in hyperbolic materials.

physics.optics↗

arXiv2024

Realizing topologically protected ghost surface polaritons by lattice transformation optics

While conventional surface waves propagate along the surface and decay perpendicularly from the interface, the ghost surface polaritons show oblique propagation direction with respect to the interface. Here, we have discovered topologically protected ghost surface polaritons by applying the lattice transformation optics method to gyromagnetic photonic crystals. By introducing the transformation optics method to periodic systems, we develop the lattice transformation optics method to engineer the band structures and propagation directions of the surface polaritons. We show that a simple shear transformation on the square lattice can tailor the propagation directions with ease. The reversed ghost surface polariton is discovered by setting a negative shear factor. Interestingly, we find the topological invariant Chern number will change sign when the orientation of the Brillouin zone flipped during the transformation. Our findings open up new avenues for studying ghost surface polaritons and provide a general engineering method for periodic systems.

physics.optics↗

arXiv2022

Negative reflection and negative refraction in biaxial van der Waals materials

Negative reflection and negative refraction are exotic phenomena that can be achieved by platforms such as double-negative metamaterial, hyperbolic metamaterial, and phase-discontinuity metasurface. Recently, natural biaxial van der Waals (vdW) materials, which support extremely anisotropic, low-loss, and highly confined polaritons from infrared to visible regime, are emerging as promising candidates for planar reflective and refractive optics. Here, we introduce three degrees of freedom, namely interface, crystal direction, and electric tunability to manipulate the reflection and refraction of the polaritons. With broken in-plane symmetry contributed by the interface and crystal direction, distinguished reflection and refraction such as negative and backward reflection, positive and negative refraction could exist simultaneously and exhibit high tunability. The numerical simulations show good consistency with the theoretical analysis. Our findings provide a robust recipe for the realization of negative reflection and refraction in biaxial vdW materials, paving the way for the polaritonics and interface nano-optics.

physics.optics↗

arXiv2022

Tailoring topological transition of anisotropic polaritons by interface engineering in biaxial crystals

Polaritons in polar biaxial crystals with extreme anisotropy offer a promising route to manipulate nanoscale light-matter interactions. The dynamical modulation of their dispersion is great significance for future integrated nano-optics but remains challenging. Here, we report a momentum-directed strategy, a coupling between the modes with extra momentum supported by the interface and in-plane hyperbolic polaritons, to tailor topological transitions of anisotropic polaritons in biaxial crystals. We experimentally demonstrate such tailored polaritons at the interface of heterostructures between graphene and α-phase molybdenum trioxide (α-MoO3). The interlayer coupling can be electrically modulated by changing the Fermi level in graphene, enabling a dynamic topological transition. More interestingly, we found that the topological transition occurs at a constant Fermi level when tuning the thickness of α-MoO3. The momentum-directed strategy implemented by interface engineering offers new insights for optical topological transitions, which may shed new light for programmable polaritonics, energy transfer and neuromorphic photonics.

physics.optics↗