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Wenyan Wang

Publications and source records attributed to Wenyan Wang.

At least 19 recordsLinked to original sources

DISTAL: Distillation and Self-Supervised Pretraining for Structure-Agnostic Materials Property Prediction

Materials property prediction remains difficult in low-data settings, where many target properties are supported by only a limited number of labeled samples. Models with the strongest predictive accuracy often depend on crystal structures, which restricts their use in early-stage screening when structural information is limited or unavailable. To address this challenge, we propose DISTAL, a dual-prior framework for structure-agnostic materials property prediction that combines self-supervised compositional pretraining with structure-aware knowledge distillation. DISTAL first learns transferable compositional representations from a large virtual composition space using 145 composition-derived descriptors. It then distills structural knowledge from a pretrained ALIGNN teacher into a composition-conditioned student. This setting allows structural priors to be used during training without requiring structural inputs at inference. By integrating explicit compositional descriptors, pretrained latent features, and distilled structural features within a unified prediction pipeline, DISTAL captures complementary signals that are difficult to recover from any single representation alone. Across 39 benchmark tasks, the best-performing multimodal configuration combines all three signals, and improves over the reference benchmark on 37 tasks. DISTAL achieves the strongest overall performance among all evaluated feature combinations. These results indicate that compositional pretraining and structural distillation provide complementary priors and offer a practical route to robust composition-only prediction in small-data materials informatics. The source code and the pre-trained models are anonymously available at: https://osf.io/eq96d/overview?view_only=451617f42f7849e08750bd1852b48980 and will be released at the official link after acceptance.

cs.LG

CMCNet: Aligning Ultrasound Image Embeddings with Textual TI-RADS Representations for Fine-Grained Thyroid Classification

Ultrasound is the primary imaging modality for assessing thyroid nodules, and the ACR TI-RADS framework standardizes diagnosis through five ultrasound feature categories that are aggregated into five risk levels (TR1-TR5). Although widely adopted in clinical practice, most deep learning approaches focus on binary malignancy classification, while multi-class prediction and explicit utilization of feature-level supervision remain underexplored, largely due to limited annotated data. In this study, we introduce the STN dataset of 600 thyroid nodules with paired transverse and longitudinal ultrasound images, bounding box annotations, and complete labels for all five TI-RADS feature categories. Following the clinical decision process, we investigate how structured feature information can guide representation learning during training while requiring only images at inference. We demonstrate that text embeddings derived from standardized feature descriptions form a stable surrogate representation for TI-RADS risk levels. Based on this observation, we propose CMCNet, which aligns image embeddings to fixed textual embeddings via a Center-Margin Contrastive Loss that simultaneously promotes intra-class compactness and inter-class separation. Experimental results show that this embedding alignment strategy is more data-efficient and robust than direct multitask learning, and consistently outperforms InfoNCE, center loss, a strong multitask baseline, and a VQA-style multimodal model, particularly in imbalanced settings. The dataset is freely available at doi: 10.5281/zenodo.19125693 and the source code is available at: https://www.healthinformaticslab.org/supp/.

cs.CV

Anomalous Low-temperature Magnetotransport in Kagome Metal CsCr$_3$Sb$_5$ under Pressure

As a unique kagome superconductor displaying clear signatures of strong electronic correlations, CsCr$_3$Sb$_5$ has drawn much attention. Its rich temperature-pressure phase diagram features intertwined orders including pressure-induced superconductivity and two density-wave-like phases, making it an outstanding platform to explore the complex coexistence and competition of multiple quantum orders. At around 30 K, which we designate as $T_3$, a possible anomaly manifesting as a hump in the resistivity has been observed, yet its nature remains largely unexplored due to limited supporting evidence from other probes. Here, we conducted systematic magnetotransport experiments under hydrostatic pressure to investigate the nature of this anomaly. Our results reveal an abundance of intriguing magnetotransport signatures below $T_3$, including a non-trivial temperature dependence of the Hall coefficient, multi-band characteristics, and pressure-enhanced anomalous-Hall-like effect. These signatures bear resemblance to those observed in the charge-density-wave state in the sister compound CsV$_3$Sb$_5$. These findings suggest the possibility of an additional, exotic electronic order in CsCr$_3$Sb$_5$, calling for further detailed investigations.

cond-mat.str-el

Giant critical current peak induced by pressure in kagome superconductor RbV$_{3}$Sb$_{5}$

Superconductivity can coexist or compete with other orders such as magnetism or density waves. Optimizing superconductivity requires identifying competing orders that may disrupt Cooper pair coherence. Here, we use the self-field critical current ($I_{\rm c,sf}$) to probe pressure-tuned superconductivity in the kagome superconductor RbV$_3$Sb$_5$. As pressure destabilizes the charge-density wave (CDW) state, $I_{\rm c,sf}$ drastically enhances, peaking near the critical pressure where the CDW state is completely suppressed at zero temperature. Surprisingly, a weaker $I_{\rm c,sf}$ peak emerges within the CDW phase. Near the pressure of the weaker peak, the superconducting phase transition temperature shifts from an increasing trend with pressure to a near plateau. Our analysis suggests the possibility of a sudden change in the CDW pattern or a Lifshitz transition, highlighting the need for microscopic examinations of the CDW state for understanding the pressure evolution of superconductivity in RbV$_3$Sb$_5$.

cond-mat.supr-con

Point-contact Andreev reflection spectroscopy of layered superconductors with device-integrated diamond anvil cells

Superconductors that can be mechanically exfoliated are an interesting platform for exploring superconducting properties tuned by layer thickness. These layered superconductors are also expected to exhibit sensitivity to applied pressure. While pressure has been demonstrated to be an effective way of tuning bulk superconductors, analogous studies on superconducting thin flakes have been limited due to technical challenges. In particular, spectroscopic measurements under pressure remain insufficiently explored. In this work, we functionalized the diamond anvil cell technique for point-contact Andreev reflection spectroscopy (PCAR) measurement on thin-flake materials under pressure, offering the opportunity to obtain spectroscopic information on superconductivity. To validate the feasibility of this method, we have conducted PCAR measurements on iron-selenide thin flakes to extract temperature-dependent superconducting gap values under ambient and high pressure. Combine with the proven magnetotransport capability, our method provides a conceptually simple tool for a detailed examination of thin-flake superconductors under pressure.

cond-mat.supr-con

GrifFinNet: A Graph-Relation Integrated Transformer for Financial Predictions

Predicting stock returns remains a central challenge in quantitative finance, transitioning from traditional statistical methods to contemporary deep learning techniques. However, many current models struggle with effectively capturing spatio-temporal dynamics and integrating multiple relational data sources. This study proposes GrifFinNet, a Graph-Relation Integrated Transformer for Financial Predictions, which combines multi-relational graph modeling with Transformer-based temporal encoding. GrifFinNet constructs inter-stock relation graphs based on industry sectors and institutional ownership, and incorporates an adaptive gating mechanism to dynamically integrate relational data in response to changing market conditions. This approach enables the model to jointly capture spatial dependencies and temporal patterns, offering a comprehensive representation of market dynamics. Extensive experiments on two Chinese A-share indices show that GrifFinNet consistently outperforms several baseline models and provides valuable, interpretable insights into financial market behavior. The code and data are available at: https://www.healthinformaticslab.org/supp/.

cs.CE

Strong coupling between a single-photon and a two-photon Fock state

The realization of strong nonlinear coupling between single photons has been a long-standing goal in quantum optics and quantum information science, promising wide impact applications, such as all-optical deterministic quantum logic and single-photon frequency conversion. Here, we report an experimental observation of the strong coupling between a single-photon and a two-photon Fock state in an ultrastrongly-coupled circuit-QED system. This strong nonlinear interaction is realized by introducing a detuned flux qubit working as an effective coupler between two modes of a superconducting coplanar waveguide resonator. The ultrastrong light--matter interaction breaks the excitation number conservation, and an external flux bias breaks the parity conservation. The combined effect of the two enables the strong one--two-photon coupling. Quantum Rabi-like avoided crossing is resolved when tuning the two-photon resonance frequency of the first mode across the single-photon resonance frequency of the second mode. Within this new photonic regime, we observe the thresholdless second harmonic generation for a mean photon number below one. Our results represent a key step towards a new regime of quantum nonlinear optics, where individual photons can deterministically and coherently interact with each other in the absence of any stimulating fields.

quant-ph

On the Spread of Graph-Related Matrices

The spread of a real symmetric matrix is defined as the difference between its largest and smallest eigenvalue. The study of graph-related matrices has attracted considerable attention, leading to a substantial body of findings. In this paper, we investigate a general spread problem related to $A_α$-matrix of graphs. The $A_α$-matrix of a graph $G$, introduced by Nikiforov in 2017, is a convex combinations of its diagonal degree matrix $D(G)$ and adjacency matrix $A(G)$, defined as $A_α (G) = αD(G) + (1-α) A(G)$. Let $λ_1^{(α)} (G)$ and $λ_n^{(α)} (G)$ denote the largest and smallest eigenvalues of $A_α (G)$, respectively. We determined the unique graph that maximizes $λ^{(α)}_1 (G) - β\cdotλ^{(γ)}_n (G)$ among all connected $n$-vertex graphs for sufficiently large $n$, where $0 \leq α< 1$, $1/2\leq γ< 1$ and $0<βγ\leq 1$. As an application, we confirm a conjecture proposed by Lin, Miao, and Guo [Linear Algebra Appl. 606 (2020) 1--22]. In addition, one of main results in [SIAM J. Discrete Math. 38 (2024) 590--608] is a simple corollary of our result by choosing $α= γ= 1/2$ and $β= 1$.

math.CO

Discovery of a new phase in thin flakes of KV$_{3}$Sb$_{5}$ under pressure

We report results of magnetotransport measurements on KV$_3$Sb$_5$ thin flakes under pressure. Our zero-field electrical resistance reveals an additional anomaly emerging under pressure ($p$), marking a previously unidentified phase boundary $T^{\rm \ast}$($p$). Together with the established $T_{\rm CDW}(p)$ and $T_c(p)$, denoting the charge-density-wave transition and a superconducting transition, respectively, the temperature-pressure phase diagram of KV$_3$Sb$_5$ features a rich interplay among multiple phases. The Hall coefficient evolves reasonably smoothly when crossing the $T^{\rm \ast}$ phase boundary compared with the variation when crossing $T_{\rm CDW}$, indicating the preservation of the pristine electronic structure. The mobility spectrum analysis provides further insights into distinguishing different phases. Finally, our high-pressure quantum oscillation studies up to 31 T combined with density functional theory calculations further demonstrate that the new phase does not reconstruct the Fermi surface, confirming that the translational symmetry of the pristine metallic state is preserved.

cond-mat.supr-con

Maximum spread of $K_r$-minor free graphs

The spread of a graph is the difference between the largest and smallest eigenvalue of its adjacency matrix. In this paper, we investigate spread problems for graphs with excluded clique-minors. We show that for sufficiently large $n$, the $n$-vertex $K_r$-minor free graph with maximum spread is the join of a clique and an independent set, with $r-2$ and $n-r+2$ vertices, respectively.

math.CO

Quantum Phase Transition as a Promising Route to Enhance the Critical Current in Kagome Superconductor CsV$_{3}$Sb$_{5}$

Developing strategies to systematically increase the critical current, the threshold current below which the superconductivity exists, is an important goal of materials science. Here, the concept of quantum phase transition is employed to enhance the critical current of a kagome superconductor CsV$_3$Sb$_5$, which exhibits a charge density wave (CDW) and superconductivity that are both affected by hydrostatic pressure. As the CDW phase is rapidly suppressed under pressure, a large enhancement in the self-field critical current ($I_{\rm c,sf}$) is recorded. The observation of a peak-like enhancement of $I_{\rm c,sf}$ at the zero-temperature limit ($I_{\rm c,sf}(0)$) centred at $p^*\approx 20$~kbar, the same pressure where the CDW phase transition vanishes, further provides strong evidence of a zero-temperature quantum anomaly in this class of pressure-tuned superconductor. Such a peak in $I_{\rm c,sf}(0)$ resembles the findings in other well-established quantum-critical superconductors, hinting at the presence of enhanced quantum fluctuations associated with the CDW phase in CsV$_3$Sb$_5$.

cond-mat.supr-con

Large Fermi surface in pristine kagome metal CsV$_3$Sb$_5$ and enhanced quasiparticle effective masses

The kagome metal CsV$_3$Sb$_5$ is an ideal platform to study the interplay between topology and electron correlation. To understand the fermiology of CsV$_3$Sb$_5$, intensive quantum oscillation (QO) studies at ambient pressure have been conducted. However, due to the Fermi surface reconstruction by the complicated charge density wave (CDW) order, the QO spectrum is exceedingly complex, hindering a complete understanding of the fermiology. Here, we directly map the Fermi surface of the pristine CsV$_3$Sb$_5$ by measuring Shubnikov-de Haas QOs up to 29 T under pressure, where the CDW order is completely suppressed. The QO spectrum of the pristine CsV$_3$Sb$_5$ is significantly simpler than the one in the CDW phase, and the detected oscillation frequencies agree well with our density functional theory calculations. In particular, a frequency as large as 8,200 T is detected. Pressure-dependent QO studies further reveal a weak but noticeable enhancement of the quasiparticle effective masses on approaching the critical pressure where the CDW order disappears, hinting at the presence of quantum fluctuations. Our high-pressure QO results reveal the large, unreconstructed Fermi surface of CsV$_3$Sb$_5$, paving the way to understanding the parent state of this intriguing metal in which the electrons can be organized into different ordered states.

cond-mat.supr-con

Convert laser light into single photons via interference

Laser light possesses perfect coherence, but cannot be attenuated to single photons via linear optics. An elegant route to convert laser light into single photons is based on photon blockade in a cavity with a single atom in the strong coupling regime. However, the single-photon purity achieved by this method remains relatively low. Here we propose an interference-based approach where laser light can be transformed into single photons by destructively interfering with a weak but super-bunched incoherent field emitted from a cavity coupling to a single quantum emitter. We demonstrate this idea by measuring the reflected light of a laser field which drives a double-sided optical microcavity containing a single artificial atom-quantum dot (QD) in the Purcell regime. The reflected light consists of a superposition of the driving field with the cavity output field. We achieve the second-order autocorrelation g2(0)=0.030+-0.002 and the two-photon interference visibility 94.3%+-0.2. By separating the coherent and incoherent fields in the reflected light, we observe that the incoherent field from the cavity exhibits super-bunching with g2(0)=41+-2 while the coherent field remains Poissonian statistics. By controlling the relative amplitude of coherent and incoherent fields, we verify that photon statistics of reflected light is tuneable from perfect anti-bunching to super-bunching in agreement with our predictions. Our results demonstrate photon statistics of light as a quantum interference phenomenon that a single QD can scatter two photons simultaneously at low driving fields in contrast to the common picture that a single two-level quantum emitter can only scatter (or absorb and emit) single photons. This work opens the door to tailoring photon statistics of laser light via cavity or waveguide quantum electrodynamics and interference.

quant-ph

Current direction dependent magnetotransport in CuTe

Despite being a layered, easily-exfoliated compound, copper monotelluride (CuTe) features an unusual quasi-one-dimensional charge density wave below $T_{\rm CDW}\approx335$ K. Within a CuTe layer, the electrical resistivity depends sensitively on the direction of the electrical current. Here, we use magnetotransport to probe the metallic state of CuTe with two distinct in-plane current directions. When the current flows along the $a$-axis ($I//a$), the magnetoresistance exhibits a downward curvature as the magnetic field increases. On the other hand, when the current is along the $b$-axis ($I//b$), the magnetoresistance shows the opposite curvature. Our analysis uncovers a violation of Kohler scaling, but only for $I//a$. Shubnikov-de Haas oscillations are detected at low temperatures. Our results shed light on the nature of the metallic state in CuTe with the development of the charge density wave.

cond-mat.str-el

The Mollow triplets under few-photon excitation

Resonant excitation is an essential tool in the development of semiconductor quantum dots (QDs) for quantum information processing. One central challenge is to enable a transparent access to the QD signal without post-selection information loss. A viable path is through cavity enhancement, which has successfully lifted the resonantly scattered field strength over the laser background under \emph{weak} excitation. Here, we extend this success to the \emph{saturation} regime using a QD-micropillar device with a Purcell factor of 10.9 and an ultra-low background cavity reflectivity of just 0.0089. We achieve a signal to background ratio of 50 and an overall system responsivity of 3~\%, i.e., we detect on average 0.03 resonantly scattered single photons for every incident laser photon. Raising the excitation to the few-photon level, the QD response is brought into saturation where we observe the Mollow triplets as well as the associated cascade single photon emissions, without resort to any laser background rejection technique. Our work offers a new perspective toward QD cavity interface that is not restricted by the laser background.

quant-ph

Similarities and Differences in the Fermiology of Kagome Metals AV$_{3}$Sb$_{5}$ (A=K, Rb, Cs) Revealed by Shubnikov-de Haas Oscillations

Materials with AV$_3$Sb$_5$ (A=K, Rb, Cs) stoichiometry are recently discovered kagome superconductors with the electronic structure featuring a Dirac band, van Hove singularities and flat bands. These systems undergo anomalous charge-density-wave (CDW) transitions at $T_{\rm CDW}$~80-100 K, resulting in the reconstruction of the Fermi surface from the pristine phase. Although comprehensive investigations of the electronic structure via quantum oscillations (QOs) have been performed on the sister compounds CsV$_3$Sb$_5$ and RbV$_3$Sb$_5$, a detailed QO study of KV$_3$Sb$_5$ is so far absent. Here, we report the Shubnikov-de Haas QO study in KV$_3$Sb$_5$. We resolve a large number of new frequencies with the highest frequency of 2202 T (occupying ~54% of the Brillouin zone area in the $k_x$-$k_y$ plane). The Lifshitz-Kosevich analysis further gives relatively small cyclotron effective masses, and the angular dependence study reveals the two-dimensional nature of the frequencies with a sufficient signal-to-noise ratio. Finally, we compare the QO spectra for all three AV$_3$Sb$_5$ compounds collected under the same conditions, enabling us to point out the similarities and differences across these systems. Our results fill in the gap of the QO study in KV$_3$Sb$_5$ and provide valuable data to understand the band structure of all three members of AV$_3$Sb$_5$.

cond-mat.supr-con

Anomalous Hall effect and two-dimensional Fermi surfaces in the charge-density-wave state of kagome metal RbV$_3$Sb$_5$

AV$_3$Sb$_5$ (A=Cs, K, Rb) are recently discovered superconducting systems ($T_{\rm c}\sim0.9-2.5$ K) in which the vanadium atoms adopt the kagome structure. Intriguingly, these systems enter a charge-density-wave (CDW) phase ($T_{\rm CDW}\sim80-100$ K), and further evidence shows that the time-reversal symmetry is broken in the CDW phase. Concurrently, the anomalous Hall effect has been observed in KV$_3$Sb$_5$ and CsV$_3$Sb$_5$ inside the novel CDW phase. Here, we report a comprehensive study of a high-quality RbV$_3$Sb$_5$ single crystal with magnetotransport measurements. Our data demonstrate the emergence of anomalous Hall effect in RbV$_3$Sb$_5$ when the charge-density-wave state develops. The magnitude of anomalous Hall resistivity at the low temperature limit is comparable to the reported values in KV$_3$Sb$_5$ and CsV$_3$Sb$_5$. The magnetoresistance channel further reveals a rich spectrum of quantum oscillation frequencies, many of which have not been reported before. In particular, a large quantum oscillation frequency (2235 T), which occupies $\sim$56% of the Brillouin zone area, has been recorded. For the quantum oscillation frequencies with sufficient signal-to-noise ratio, we further perform field-angle dependent measurements and our data indicate two-dimensional Fermi surfaces in RbV$_3$Sb$_5$. Our results provide indispensable information for understanding the anomalous Hall effect and band structure in kagome metals AV$_3$Sb$_5$.

cond-mat.supr-con

Nodeless superconductivity in kagome metal CsV$_{3}$Sb$_{5}$ with and without time reversal symmetry breaking

The kagome metal CsV$_{3}$Sb$_{5}$ features an unusual competition between the charge-density-wave (CDW) order and superconductivity. Evidence for time-reversal symmetry breaking (TRSB) inside the CDW phase has been accumulating. Hence, the superconductivity in CsV$_{3}$Sb$_{5}$ emerges from a TRSB normal state, potentially resulting in an exotic superconducting state. To reveal the pairing symmetry, we first investigate the effect of nonmagnetic impurity. Our results show that the superconducting critical temperature is insensitive to disorder, pointing to conventional $s$-wave superconductivity. Moreover, our measurements of the self-field critical current ($I_{c,sf}$), which is related to the London penetration depth, also confirm conventional $s$-wave superconductivity with strong coupling. Finally, we measure $I_{c,sf}$ where the CDW order is removed by pressure and superconductivity emerges from the pristine normal state. Our results show that $s$-wave gap symmetry is retained, providing strong evidence for the presence of conventional $s$-wave superconductivity in CsV$_{3}$Sb$_{5}$ irrespective of the presence of the TRSB

cond-mat.supr-con