arXiv subjects

Dapeng Yao

Publications and source records attributed to Dapeng Yao.

10 recordsLinked to original sources

arXiv2026

Chirality-Selective Phonon Pumping by Ferroelectric Dynamics

The discovery of chiral phonons has expanded the conventional view of lattice vibrations as passive heat carriers, opening new opportunities for phononic spintronic devices. However, their realization has been largely limited to chiral crystals or to specific regions of momentum space in certain achiral materials. Here, we propose a generic mechanism for generating propagating chiral phonons in an ordinary dielectric through the precession of the electric polarization in an adjacent ferroelectric. The polarization dynamics transfers its intrinsic angular momentum to the lattice via electrostrictive coupling, thereby pumping chirality-selective phonons whose handedness is dictated by that of the polarization precession. For a typical LiNbO$_{3}$$|$Y$_{3}$Al$_{5}$O$_{12}$ bilayer, we find that the pumping efficiency quantified by an interfacial convertance substantially exceeds those of thermally induced chiral-phonon generation in chiral crystals, owing to the strong electrostrictive coupling in ferroelectrics. Our work establishes ferroelectric dynamics as a versatile electrical source of chiral phonons and provides a general route toward electrically programmable chiral-phononic and spintronic functionalities.

cond-mat.mes-hall↗

arXiv2026

Magnetism and Topology from Circularly Polarized Phonon Floquet Engineering

We theoretically show that circularly polarized phonons induce electronic magnetization and drive a topological phase transition via phonon Floquet engineering. Considering the electronic states modulated by circularly polarized phonons on a honeycomb lattice, we show that such lattice dynamics generates an effective next-nearest-neighbor electron hopping, leading to a Haldane-type mass term. Circularly polarized phonon breaks time-reversal symmetry (TRS) and opens a gap at valley points, undergoing phase transition from a trivial insulator to a Chern insulator. Moreover, the orbital and spin magnetizations emerge due to the breaking of TRS. Our results show that circularly polarized phonons serve as an effective magnetic field to engineer magnetism and topology, offering new opportunities for phonon Floquet approaches.

cond-mat.mes-hall↗

arXiv2025

Dynamical Orbital Angular Momentum Induced by Circularly Polarized Phonons

We show that the orbital angular momentum (OAM) of electrons is dynamically induced by circularly polarized phonons. The induced OAM originates from the adiabatic evolution in which electrons acquire Berry phase formulated in terms of the Berry curvature encoded in phonon displacement space. By introducing a tight-binding model with $p$ orbitals on a honeycomb lattice, we show a microscopic picture that ionic rotations modulate orbital overlaps of electrons, and calculate the generated OAM, whose sign depends on phonon chirality. We then construct an effective model for valley phonons with different phonon pseudoangular momenta (PAM) and identity their distinct intervalley-scattering channels. Our model obeys the selection rule between phonons and electrons with the orbital degree of freedom. Extending this framework to $d$-orbital electrons, our model is applied to describe the induced OAM in monolayer transition metal dichalcogenides. Our results reveal a direct orbital generation mechanism that emerges even in materials with weak spin-orbital coupling, opening a new promising way for orbitronics applications.

cond-mat.mes-hall↗

arXiv2025

LMAR: Language Model Augmented Retriever for Domain-specific Knowledge Indexing

Retrieval Augmented Generation (RAG) systems often struggle with domain-specific knowledge due to performance deterioration of pre-trained embeddings and prohibitive computational costs of large language model (LLM)-based retrievers. While fine-tuning data augmentation embedding models offers a promising direction, its effectiveness is limited by the need for high-quality training data and reliable chunking strategies that preserve contextual integrity. We propose LMAR (Language Model Augmented Retriever), a model-agnostic framework that addresses these challenges by combining LLM-guided data synthesis with contrastive embedding adaptation and efficient text clustering. LMAR consists of a two-stage pipeline: (1) Triplet sampling and synthetic data augmentation, where LLMs act as both labeler and validator to ensure high-fidelity supervision throughout the pipeline. Experimental results across multiple domain-specific benchmark datasets demonstrate that LMAR outperforms multiple baseline models, while maintaining moderate hardware requirements and low latency. Its model-agnostic nature further enables seamless integration with emerging RAG architectures and text embedding models, ensuring continual improvements without redesigning the pipeline. These results highlight LMAR as a practical and cost-effective solution for scalable domain-specific adaptation.

cs.IR↗

arXiv2025

Theory of spin magnetization driven by chiral phonons

We construct a general theory of spin magnetization driven by chiral phonons under an adiabatic process, in which atoms rotate around their equilibrium positions with a low phonon frequency. Here the spin magnetization originates from the modulated electronic states with spin-orbital coupling by atomic rotations. Under the adiabatic approximation, the time-dependent spin magnetization can be calculated by a Berry-phase method. In this paper, we focus on its time average, which is evaluated by assuming that the phonon displacement is small. As a result, the time average of the spin magnetization is concisely formulated in the form of the Berry curvature defined in the phonon-displacement space as an intrinsic property of atomic rotations. Our formula for spin magnetization reflects the chiral nature of phonons, and is convenient for $ab$ $initio$ calculations.

cond-mat.mes-hall↗

arXiv2025

Chiral magnon in ferromagnetic chiral crystals

We theoretically propose chiral magnon in ferromagnetic chiral crystals. We show that the crystal chirality is imprinted in orbital angular momentum of magnons which exhibits the opposite signs for opposite chiralities of the crystal. We also show that a finite magnon orbital angular momentum can be induced by a temperature gradient which is a magnonic analogue of the Edelstein effect.

cond-mat.mes-hall↗

arXiv2024

Electric field-induced nonreciprocal spin current due to chiral phonons in chiral-structure superconductors

The recent experiment [R. Nakajima, et al., Nature 613, 479 (2023)] has reported a pair of oppositely polarized spins under an alternating electric current in a superconductor with a chiral structure. However, these behaviors cannot be explained by the conventional Edelstein effect and require a new mechanism. In this Letter, we propose a mechanism of spin current generation under an external electric field due to chiral phonons in a chiral-structure superconductor based on the Bogoliubov de Gennes and the Boltzmann equations. In our mechanism, chiral phonons are induced by electric field due to inversion symmetry breaking and electron-phonon interaction. They work as an effective Zeeman field and hence spin-polarize Bogoliubov quasiparticles in the superconductor. As a result, the spin current carried by quasiparticles flows along the screw axis and shows a quadratic dependence on the electric field at the low-field range, leading to a nonreciprocal spin transport. The spin current also shows a nonmonotonic temperature dependence and has a maximum at around the superconducting transition temperature.

cond-mat.mes-hall↗

arXiv2024

Bayesian Sparse Gaussian Mixture Model in High Dimensions

We study the sparse high-dimensional Gaussian mixture model when the number of clusters is allowed to grow with the sample size. A minimax lower bound for parameter estimation is established, and we show that a constrained maximum likelihood estimator achieves the minimax lower bound. However, this optimization-based estimator is computationally intractable because the objective function is highly nonconvex and the feasible set involves discrete structures. To address the computational challenge, we propose a Bayesian approach to estimate high-dimensional Gaussian mixtures whose cluster centers exhibit sparsity using a continuous spike-and-slab prior. Posterior inference can be efficiently computed using an easy-to-implement Gibbs sampler. We further prove that the posterior contraction rate of the proposed Bayesian method is minimax optimal. The mis-clustering rate is obtained as a by-product using tools from matrix perturbation theory. The proposed Bayesian sparse Gaussian mixture model does not require pre-specifying the number of clusters, which can be adaptively estimated via the Gibbs sampler. The validity and usefulness of the proposed method is demonstrated through simulation studies and the analysis of a real-world single-cell RNA sequencing dataset.

math.ST↗

arXiv2023

Conversion of chiral phonons into magnons in ferromagnets and antiferromagnets

Chiral phonons with atomic rotations converted into electron spins result in a change of spin magnetizations in crystals. In this paper, we investigate a new conversion of chiral phonons into magnons both in ferromagnets and antiferromagnets by spin models with exchange and Dzyaloshinskii-Moriya interactions. The atomic rotations in chiral phonons are treated as slow phonons, which modulate spin-spin interaction and induce time-dependent magnon excitations due to geometric effect within adiabatic approximation. We demonstrate that a non-trivial change of the number of magnons requires breaking of the spin-rotation symmetry around the spin quantization axis. As a result, the clockwise and counterclockwise chiral phonons induce a change of the magnon number with opposite signs, which corresponds to an increasing or decreasing spin magnetizaton due to the chiral nature of the atomic rotations. In particular, in antiferromagnets, the modulation of magnons due to chiral phonons generates a non-zero net magnetization by the proposed effect, which is expect to be observed in experiments.

cond-mat.mes-hall↗

arXiv2022

Chiral-phonon-induced current in helical crystals

In this study, we theoretically show that in a helical crystal, a current is induced by chiral phonons representing the microscopic local rotation of atoms. By treating the rotational motion as a perturbation, we calculate the time-dependent current by using the adiabatic Berry phase method. The time average of the current along the helical axis becomes finite in the metallic phase but it vanishes in the insulating phase. On the other hand, the current in the hexagonal plane changes with time, but its time average vanishes due to the threefold rotation space-time symmetry. We show that the time evolutions of the current follow the space-time symmetries of the helical systems. Moreover, we explain the reason for the vanishing of the time average of the current in the insulating phase from the aspect of the Chern number in the parameter space.

cond-mat.mes-hall↗