arXiv subjects

X. Yin

Publications and source records attributed to X. Yin.

6 recordsLinked to original sources

arXiv2025

A decoupled and structure-preserving direct discontinuous Galerkin method for the Keller-Segel Model

In this work, we develop a novel numerical scheme to solve the classical Keller--Segel (KS) model which simultaneously preserves its intrinsic mathematical structure and achieves optimal accuracy. The model is reformulated into a gradient flow structure using the energy variational method, which reveals the inherent energy dissipative dynamics of the system. Based on this reformulation, we construct a structure-preserving discretization by semi-implicit method in time and the direct discontinuous Galerkin (DDG) method in space, resulting in a stable and high-order accurate approximation. The proposed scheme enjoys several desirable properties: (i) energy stability, ensuring discrete free energy dissipation; (ii) exact conservation of mass for the cell density; (iii) positivity preservation of the numerical cell density, enforced via a carefully designed limiter; and (iv) optimal convergence rate, with first-order accuracy in time and $(k+1)$-th order accuracy in space for polynomials of degree $k$. We provide rigorous theoretical analysis that substantiate these properties. In addition, extensive numerical experiments, including benchmark problems exhibiting pattern formation and near blow-up behavior, are conducted to validate the theoretical results and demonstrate the robustness, efficiency, and accuracy of the proposed method. The approach offers a flexible and reliable framework for structure-preserving numerical simulation of chemotaxis models and other gradient flow-type systems.

math.NA↗

arXiv2022

Metasurface-Stabilized Optical Microcavities

We demonstrate stable optical microcavities by counteracting the phase evolution of the cavity modes using an amorphous silicon metasurface as one of the two cavity end mirrors. Careful design allows us to limit the metasurface scattering losses at telecom wavelengths to less than 2% and using a distributed Bragg reflector as metasurface substrate ensures high reflectivity. Our first demonstration experimentally achieves telecom-wavelength microcavities with quality factors of up to 4600, spectral resonance linewidths below 0.4 nm, and mode volumes down to below 2.7$\lambda ^3$. We then show that the method introduces unprecedented freedom to stabilize modes with arbitrary transverse intensity profiles and design cavity-enhanced hologram modes. Our approach introduces the nanoscopic light control capabilities of dielectric metasurfaces to cavity electrodynamics and is directly industrially scalable using widespread semiconductor manufacturing processes.

physics.optics↗

arXiv2021

Slow Light Nanocoatings for Ultrashort Pulse Shaping

Transparent materials do not absorb light but have profound influence on the phase evolution of transmitted radiation. One consequence is chromatic dispersion, i.e., light of different frequencies travels at different velocities, causing ultrashort laser pulses to elongate in time while propagating. Here we experimentally demonstrate ultrathin nanostructured coatings that resolve this challenge: we tailor the dispersion of silicon nanopillar arrays such that they temporally reshape pulses upon transmission using slow light effects and act as ultrashort laser pulse compressors. The coatings induce anomalous group delay dispersion in the visible to near-infrared spectral region around 800 nm wavelength over an 80 nm bandwidth. We characterize the arrays' performance in the spectral domain via white light interferometry and directly demonstrate the temporal compression of femtosecond laser pulses. Applying these coatings to conventional optics renders them ultrashort pulse compatible and suitable for a wide range of applications.

physics.optics↗

arXiv2018

Evidence for unconventional superconductivity in Half-Heusler YPdBi and TbPdBi compounds revealed by London penetration depth measurements

The half-Heusler compounds YPdBi and TbPdBi, while having similar band structure, exhibit different magnetic properties. YPdBi is a diamagnet, while TbPdBi shows antiferromagnetic order below 5.5 K. Both are superconductors with T${_c}\approx$1 K for YPdBi and T${_c}\approx$1.75 K for TbPdBi. Such a contrast in properties between these two compounds opens a question about the effects of band structure or magnetic correlations on superconductivity. Using the combination of a tunnel diode oscillator (TDO) and a commercial dilution refrigerator, we measured temperature dependent magnetic penetration depth $Δλ(T)$ in single crystals of YPdBi and TbPdBi, down to temperatures as low as 0.1K. We found that penetration depths of both compounds do not show exponential temperature dependence and saturation at low temperatures, as expected for conventional BCS superconductors. Instead, in both compounds, the penetration depth can be described by a power law $Δλ(T) = A\times T^{n}$. The coefficient A was found to be about 50$\%$ smaller in TbPdBi, but the exponents are very similar, $n = 2.76\pm 0.04$ in YPdBi and $n = 2.6\pm 0.3$ in TbPdBi, respectively. Our results suggest unconventional superconductivity in both YPdBi and TbPdBi.

cond-mat.supr-con↗

arXiv2018

Polarization-Controlled Coherent Phonon Generation in Acousto-Plasmonic Metasurfaces

Acoustic vibrations at the nanoscale (GHz-THz frequencies) and their interactions with electrons, photons and other excitations are the heart of an emerging field in physics: nanophononics. The design of ultrahigh frequency acoustic-phonon transducers, with tunable frequency, and easy to integrate in complex systems is still an open and challenging problem for the development of acoustic nanoscopies and phonon lasers. Here we show how an optimized plasmonic metasurface can act as a high-frequency phonon transducer. We report pump-probe experiments in metasurfaces composed of an array of gold nanostructures, revealing that such arrays can act as efficient and tunable photon-phonon transducers, with a strong spectral dependence on the excitation rate and laser polarization. We anticipate our work to be the starting point for the engineering of phononic metasurfaces based on plasmonic nanostructures.

cond-mat.mes-hall↗

arXiv2006

New Connections Between 4D and 5D Black Holes

A simple equality is proposed between the BPS partition function of a general 4D IIA Calabi-Yau black hole and that of a 5D spinning M-theory Calabi-Yau black hole. Combining with recent results then leads to a new relation between the 5D spinning BPS black hole partition function and the square of the N=2 topological string partition function.

hep-th↗