arXiv subjects

Lihong Yang

Publications and source records attributed to Lihong Yang.

8 recordsLinked to original sources

arXiv2026

Unusual Dual Flat Bands and two-dimensional Dirac-node Arc State in Kagome Metal Ni3In2S2

Kagome materials are at the frontier of condensed matter physics. An ideal kagome lattice features only one geometrically frustrated flat band spanning the entire momentum space and a single Dirac cone at the Brillouin-zone corners. However, for the first time, here we observe unusual flat-band and Dirac physics in the newly discovered "322" kagome material Ni3In2S2 by combining high-resolution synchrotron- and laser-based angle-resolved photoemission spectroscopy with a micro-focused beam, scanning tunneling microscopy, and first-principles calculations. We resolve two distinct electronic flat-band states located in close proximity to the Fermi level: a robust Topological Surface Flat Band at ~40 meV below the Fermi level on the Sulfur-terminated surface, originating from weak topological insulator states, and a kagome lattice-derived flat band at ~100 meV binding energy with an ultranarrow bandwidth (~5 meV). Instead of the single Dirac cone, the Indium-terminated surface hosts a rare two-dimensional Dirac-node arc state, where the gapless Dirac nodes extend along an open one-dimensional line crossing the Brillouin-zone boundary, exhibiting sharp linear dispersion, exceptionally high Fermi velocity, and pronounced circular dichroism. These findings establish Ni3In2S2 as a unique topological kagome metal in which multiple flat-band states of different physical origin coexist with an unusual Dirac-node arc, opening an avenue for discovering flat-band--driven and topology-enabled quantum phenomena.

cond-mat.mtrl-sci↗

arXiv2026

Yet another doubly refined enumeration of Alternating Sign Matrices

Since the alternating sign matrix conjecture, proposed by Mills, Robbins, and Rumsey in 1982, was proved by Zeilberger and Kuperberg, several refined enumerations have been considered. In particular, Behrend et al. obtained a quadruply refined enumeration by adding certain parameters. In this paper, we revisit the doubly refined enumeration of alternating sign matrices by adding three parameters: the number of $-1$'s, the position of the $1$ in the first row, and the position of the $1$ in the last row. Using Lascoux's formula on symmetry functions, we derive a new determinantal formula for this doubly refined enumeration. Besides the enumeration conjecture, Mills et al. also proposed a decomposition conjecture, which was subsequently proven by Kuperberg. We present a refinement of that decomposition conjecture.

math.CO↗

arXiv2025

A Self-Conjugate Partition Analog of $(t,t+1)$-Core Partitions with Distinct Parts

Simultaneous core partitions have been widely studied in the past 20 years. In 2013, Amdeberhan gave several conjectures on the number, the average size, and the largest size of $(t,t+1)$-core partitions with distinct parts, which was proved and generalized by Straub, Xiong, Nath-Sellers, Zaleski-Zeilberger, Paramonov, and many other mathematicians. In this paper, we introduce a proper self-conjugate partition analog of $(t,t+1)$-core partitions with distinct parts, and derive the number, the average size, and the largest size for such core partitions.

math.CO↗

arXiv2024

A Concept-based Interpretable Model for the Diagnosis of Choroid Neoplasias using Multimodal Data

Diagnosing rare diseases presents a common challenge in clinical practice, necessitating the expertise of specialists for accurate identification. The advent of machine learning offers a promising solution, while the development of such technologies is hindered by the scarcity of data on rare conditions and the demand for models that are both interpretable and trustworthy in a clinical context. Interpretable AI, with its capacity for human-readable outputs, can facilitate validation by clinicians and contribute to medical education. In the current work, we focus on choroid neoplasias, the most prevalent form of eye cancer in adults, albeit rare with 5.1 per million. We built the so-far largest dataset consisting of 750 patients, incorporating three distinct imaging modalities collected from 2004 to 2022. Our work introduces a concept-based interpretable model that distinguishes between three types of choroidal tumors, integrating insights from domain experts via radiological reports. Remarkably, this model not only achieves an F1 score of 0.91, rivaling that of black-box models, but also boosts the diagnostic accuracy of junior doctors by 42%. This study highlights the significant potential of interpretable machine learning in improving the diagnosis of rare diseases, laying a groundwork for future breakthroughs in medical AI that could tackle a wider array of complex health scenarios.

cs.LG↗

arXiv2022

On a conjecture concerning the shuffle-compatible permutation statistics

The notion of shuffle-compatible permutation statistics was implicit in Stanley's work on P-partitions and was first explicitly studied by Gessel and Zhuang. The aim of this paper is to prove that the triple ${\rm (udr, pk, des)}$ is shuffle-compatible as conjectured by Gessel and Zhuang, where ${\rm udr}$ denotes the number of up-down runs, ${\rm pk}$ denotes the peak number, and ${\rm des}$ denotes the descent number. This is accomplished by establishing an ${\rm (udr, pk, des)}$-preserving bijection in the spirit of Baker-Jarvis and Sagan's bijective proofs of shuffle-compatibility property of permutation statistics. As an application, our bijection also enables us to prove that the pair $({\rm cpk}, {\rm cdes})$ is cyclic shuffle-compatible, where ${\rm cpk}$ denotes the cyclic peak number and ${\rm cdes}$ denotes the cyclic descent number.

math.CO↗

arXiv2021

Partial $γ$-Positivity for Quasi-Stirling Permutations of Multisets

We prove that the enumerative polynomials of quasi-Stirling permutations of multisets with respect to the statistics of plateaux, descents and ascents are partial $γ$-positive, thereby confirming a recent conjecture posed by Lin, Ma and Zhang. This is accomplished by proving the partial $γ$-positivity of the enumerative polynomials of certain ordered labeled trees, which are in bijection with quasi-Stirling permutations of multisets. As an application, we provide an alternative proof of the partial $γ$-positivity of the enumerative polynomials on Stirling permutations of multisets.

math.CO↗

arXiv2021

Quasi-Stirling Permutations on Multisets

A permutation $π$ of a multiset is said to be a {\em quasi-Stirling } permutation if there does not exist four indices $i<j<k<\ell$ such that $π_i=π_k$ and $π_j=π_{\ell}$. Define $$ \overline{Q}_{\mathcal{M}}(t,u,v)=\sum_{π\in \overline{\mathcal{Q}}_{\mathcal{M}}}t^{des(π)}u^{asc(π)}v^{plat(π)},$$ where $\overline{\mathcal{Q}}_{\mathcal{M}}$ denotes the set of quasi-Stirling permutations on the multiset $\mathcal{M}$, and $asc(π)$ (resp. $des(π)$, $plat(π)$) denotes the number of ascents (resp. descents, plateaux) of $π$. Denote by $\mathcal{M}^σ$ the multiset $\{1^{σ_1}, 2^{σ_2}, \ldots, n^{σ_n}\}$, where $σ=(σ_1, σ_2, \ldots, σ_n)$ is an $n$-composition of $K$ for positive integers $K$ and $n$. In this paper, we show that $\overline{Q}_{\mathcal{M}^σ}(t,u,v)=\overline{Q}_{\mathcal{M}^τ}(t,u,v)$ for any two $n$-compositions $σ$ and $τ$ of $K$. This is accomplished by establishing an $(asc, des, plat)$-preserving bijection between $\overline{\mathcal{Q}}_{\mathcal{M}^σ}$ and $\overline{\mathcal{Q}}_{\mathcal{M}^τ}$. As applications, we obtain generalizations of several results for quasi-Stirling permutations on $\mathcal{M}=\{1^k,2^k, \ldots, n^k\}$ obtained by Elizalde and solve an open problem posed by Elizalde.

math.CO↗

arXiv2012

Pressure-Driven Quantum Criticality in An Iron-Selenide Superconductor

The discovery of superconductivity of about 30 K in iron selenides with very large magnetic moments simulates the examination of completing orders. Here we report a finding of pressure- induced suppression of the superconducting transition temperature Tc and enhancement of the temperature of the resistance hump TH through charge transfer between two iron sites with different occupancies. The activation energy for the electric transport of the high-temperature resistance is observed to go to zero at a critical pressure of 8.7 GPa, at which superconductivity tends to disappear and the semiconductor-to-metal transition takes place. Beyond the critical point, the resistance exhibits a metallic behavior over the whole temperature range studied. All these features indicate the existence of quantum criticality in iron-selenide superconductors.

cond-mat.supr-con↗