arXiv subjects

Bofeng Zhu

Publications and source records attributed to Bofeng Zhu.

5 recordsLinked to original sources

arXiv2026

Dirac branch-cut modes with relativistic transport

Emergent Dirac fields, exhibiting effective relativistic physics, are most commonly associated with bulk and surface states in materials such as graphene and topological insulators. Here we identify a previously unexplored class of Dirac states that propagate along branch-cut defects in a complex Dirac mass field, unlike the well-known Jackiw-Rebbi and Jackiw-Rossi states localized at domain-wall and vortex defects. These traveling-wave defect states, termed Dirac branch-cut (DBC) modes, obey an effective one-dimensional relativistic Dirac equation with a reduced mass determined by the phase difference across the branch cut. Using acoustic metamaterials, we experimentally demonstrate a range of relativistic phenomena exhibited by DBC modes, including relativistic dispersion, energy-independent confinement, Klein tunnelling, and transport along freeform (e.g., spiral) trajectories. Our results establish branch-cut defects as a distinct mechanism for Dirac defect states beyond domain walls and vortices, and extend relativistic Dirac physics from bulk and surface states to propagating modes confined to defect boundaries.

physics.optics↗

arXiv2025

Topological photonic crystal fibre

Photonic crystal fibres (PCFs) are optical fibres that guide light using a modulated dielectric medium. They provide an exceptionally versatile platform for various applications, thanks to the flexibility with which light-guiding can be customised by modifying the fibre geometry. Here, we realise a PCF with guided modes produced by photonic bandstructure topology rather than conventional mode-trapping mechanisms. The design, which is compatible with the stack-and-draw fabrication process, consists of a cross-sectional photonic topological crystalline insulator with a disclination. A bulk-defect correspondence produces degenerate topological modes, lying below the cladding light line. We use various theoretical methods to confirm their topological origins, including a spectral localiser that makes minimal assumptions about the bandstructure. Our experiments on the fabricated topological fibre show it transmitting visible to near-infrared light with low losses of 10--20 dB/km, which do not increase much when the fibre is bent. A comparable solid-core PCF of conventional design exhibits substantially higher bending losses. Optical fibres based on topological modes thus hold promise for improved performance and novel functionalities.

physics.optics↗

arXiv2024

Versatile Braiding of Non-Hermitian Topological Edge States

Among the most intriguing features of non-Hermitian (NH) systems is the ability of complex energies to form braids under parametric variation. Several braiding behaviors, including link and knot formation, have been observed in experiments on synthetic NH systems, such as looped optical fibers. The exact conditions for these phenomena remain unsettled, but existing demonstrations have involved long-range nonreciprocal hoppings, which are hard to implement on many experimental platforms. Here, we present a route to realizing complex energy braids using 1D NH Aubry-André-Harper lattices. Under purely local gain and loss modulation, the eigenstates exhibit a variety of braiding behaviors, including unknots, Hopf links, trefoil knots, Solomon links and catenanes. We show how these are created by the interplay between non-Hermiticity and the lattice's bulk states and topological edge states. The transitions between different braids are marked by changes in the global Berry phase of the NH lattice.

physics.optics↗

arXiv2023

Topological Transitions with an Imaginary Aubry-Andre-Harper Potential

We study one-dimensional lattices with imaginary-valued Aubry-Andre-Harper (AAH) potentials. Such lattices can host edge states with purely imaginary eigenenergies, which differ from the edge states of the Hermitian AAH model and are stabilized by a non-Hermitian particle-hole symmetry. The edge states arise when the period of the imaginary potential is a multiple of four lattice constants. They are topological in origin, and can manifest on domain walls between lattices with different modulation periods and phases, as predicted by a bulk polarization invariant. Interestingly, the edge states persist and remain localized even if the real line gap closes. These features can be used in laser arrays to select topological lasing modes under spatially extended pumping.

quant-ph↗

arXiv2016

A Selective Metasurface Absorber with An Amorphous Carbon Interlayer for Solar Thermal Applications

This paper presents fabrication, measurement and modelling results for a metal-dielectric-metal metasurface absorber for solar thermal applications. The structure uses amorphous carbon as an inter-layer between thin gold films with the upper film patterned with a 2D periodic array using focused ion beam etching. The patterned has been optimised to give high absorptance from 400-1200nm and low absorptance above this wavelength range to minimise thermal radiation and hence obtain higher temperature performance. Wide angle absorptance results are shown and detailed modelling of a realistic nanostructured upper layer results in excellent agreement between measured and modelled results. The use of gold in this paper is a first step towards a high temperature metasurface where gold can be replaced by other refractory metals such as tungsten or chrome.

physics.optics↗