arXiv subjects

Yongqian Wang

Publications and source records attributed to Yongqian Wang.

7 recordsLinked to original sources

arXiv2026

V2A-DPO: Omni-Preference Optimization for Video-to-Audio Generation

This paper introduces V2A-DPO, a novel Direct Preference Optimization (DPO) framework tailored for flow-based video-to-audio generation (V2A) models, incorporating key adaptations to effectively align generated audio with human preferences. Our approach incorporates three core innovations: (1) AudioScore-a comprehensive human preference-aligned scoring system for assessing semantic consistency, temporal alignment, and perceptual quality of synthesized audio; (2) an automated AudioScore-driven pipeline for generating large-scale preference pair data for DPO optimization; (3) a curriculum learning-empowered DPO optimization strategy specifically tailored for flow-based generative models. Experiments on benchmark VGGSound dataset demonstrate that human-preference aligned Frieren and MMAudio using V2A-DPO outperform their counterparts optimized using Denoising Diffusion Policy Optimization (DDPO) as well as pre-trained baselines. Furthermore, our DPO-optimized MMAudio achieves state-of-the-art performance across multiple metrics, surpassing published V2A models.

cs.SD↗

arXiv2025

Strongly enhanced topological quantum phases in dual-surface AlO$_x$-encapsulated MnBi$_2$Te$_4$

The topological quantum phases in antiferromagnetic topological insulator MnBi$_2$Te$_4$ hold promise for next-generation spintronics, but their experimental realization has been constrained by challenges in preparing high-quality devices. In this work, we report a new wax-assisted exfoliation and transfer method that enables the fabrication of MnBi$_2$Te$_4$ heterostructures with both surfaces encapsulated by AlO$_x$. This strategy strongly enhances the topological quantum phases in MnBi$_2$Te$_4$ flakes. We observe the robust axion insulator state in even-layer device with wide zero Hall plateau and high longitudinal resistivity, and the quantum anomalous Hall effect in odd-layer device with large hysteresis and sharp plateau transition. These results demonstrate that the combination of wax exfoliation and AlO$_x$ encapsulation provides great potentials for exploring novel topological quantum phenomena and potential applications in MnBi$_2$Te$_4$ and other two-dimensional materials.

cond-mat.mtrl-sci↗

arXiv2025

Tailoring Neel orders in Layered Topological Antiferromagnets

In the two-dimensional limit, the interplay between Neel order and band topology in van der Waals topological antiferromagnets can give rise to novel quantum phenomena in the quantum anomalous Hall state, including the cascaded quantum phase transition and spin-modulation effect. However, due to the absence of net magnetization in antiferromagnets, probing the energetically degenerate Neel orders has long remained a significant challenge. Inspired by recent advances in realizing the quantum anomalous Hall effect in AlOx-capped layered topological antiferromagnet MnBi2Te4, we demonstrate deterministic control over the Neel order through surface anisotropy engineering enabled by the AlOx capping layer. By tuning the surface anisotropy, we uncover paritydependent symmetry breaking states that manifest as distinct odd-even boundary architectures, including 180 degree domain walls or continuous spin structures. Comparative studies between AlOx-capped and pristine odd-layer MnBi2Te4 flakes using domain-resolved magnetic force microscopy reveal pronounced differences in coercivity and magnetization-reversal dynamics. Notably, an unconventional giant exchange bias, which arises from perpendicular magnetic anisotropy rather than traditional interface pinning mechanisms, is observed for the first time. Our findings establish a pathway for manipulating Neel order through surface modification in A-type antiferromagnets, offering new opportunities for spintronic devices and quantum information technologies.

cond-mat.mes-hall↗

arXiv2024

Second harmonic generation induced by gate voltage oscillation in few layer MnBi2Te4

Nonlinear charge transport, such as nonreciprocal longitudinal resistance and nonlinear Hall effect, has attracted considerable interest in probing the symmetries and topological properties of new materials. Recent research has revealed significant nonreciprocal longitudinal resistance and nonlinear Hall effect in MnBi2Te4, an intrinsic magnetic topological insulator, induced by the quantum metric dipole. However, the inconsistent response with charge density and conflicting C3z symmetry requirement necessitate a thorough understanding of factors affecting the nonlinear transport measurement. This study uncovers an experimental factor leading to significant nonlinear transport signals in MnBi2Te4, attributed to gate voltage oscillation from the application of large alternating current. Additionally, a methodology is proposed to suppress this effect by individually grounding the voltage electrodes during second-harmonic measurements. The investigation underscores the critical importance of assessing the impact of gate voltage oscillation before determining the intrinsic nature of nonlinear transport in 2D material devices with an electrically connected operative gate electrode.

cond-mat.mtrl-sci↗

arXiv2024

Towards the Quantized Anomalous Hall effect in AlO$_x$-capped MnBi$_2$Te$_4$

The quantum anomalous Hall effect in layered antiferromagnet MnBi$_2$Te$_4$ harbors a rich interplay between magnetism and topology, holding a significant promise for low-power electronic devices and topological antiferromagnetic spintronics. In recent years, MnBi$_2$Te$_4$ has garnered considerable attention as the only known material to exhibit the antiferromagnetic quantum anomalous Hall effect. However, this field faces significant challenges as realizing quantized transport at zero magnetic fields depends critically on fabricating high-quality device. In this article, we address the detrimental influences of fabrication on MnBi$_2$Te$_4$ by simply depositing an AlO$_x$ thin layer on the surface prior to fabrications. Optical contrast and magnetotransport measurements on over 50 samples demonstrate that AlO$_x$ can effectively preserve the pristine state of the samples and significantly enhance the anomalous Hall effect towards quantization. Scaling analysis reveals the Berry curvature dominated mechanism of the anomalous Hall effect at various magnetic configurations. By adjusting the gate voltage, we uncover a gate independent antiferromagnetism in MnBi$_2$Te$_4$. Our experiment not only pave the way for fabricating high-quality transport devices but also advance the exploration of exotic quantum physics in 2D materials.

cond-mat.mtrl-sci↗

arXiv2024

Antiferromagnetic Quantum Anomalous Hall Effect Modulated by Spin Flips and Flops

The interplay between nontrivial band topology and layered antiferromagnetism in MnBi2Te4 has opened up a new avenue for exploring topological phases of matter. Representative examples include the quantum anomalous Hall effect and axion insulator state observed in odd and even number layers of MnBi2Te4, when the top and bottom surfaces have parallel and antiparallel spin alignments respectively. The rich and complex spin dynamics associated with the van der Waals antiferromagnetic order is expected to generate novel topological phases and phase transitions that are unique to MnBi2Te4. Here we fabricate a device of 7-septuple-layer MnBi2Te4 covered with AlOx capping layer, which enables the investigation of antiferromagnetic quantum anomalous Hall effect over wide parameter spaces. By tuning the gate voltage and perpendicular magnetic field, we uncover a cascade of quantum phase transitions that can be attributed to the influence of spin configurations on charge transport. Furthermore, we find that an in-plane magnetic field enhances both the coercive field and exchange gap of the surface state, in sharp contrast to that in ferromagnetic quantum anomalous Hall state. We propose that these peculiar features arise from the spin flip and flop transitions inherent to van der Waals antiferromagnet. The versatile tunability of the quantum anomalous Hall effect in MnBi2Te4 paves the way for potential applications in topological antiferromagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2024

Fabrication-induced even-odd discrepancy of magnetotransport in few-layer MnBi$_2$Te$_4$

The van der Waals antiferromagnetic topological insulator MnBi2Te4 represents a promising platform for exploring the layer-dependent magnetism and topological states of matter. Recently observed discrepancies between magnetic and transport properties have aroused controversies concerning the topological nature of MnBi2Te4 in the ground state. In this article, we demonstrate that fabrication can induce mismatched even-odd layer dependent magnetotransport in few-layer MnBi2Te4. We perform a comprehensive study of the magnetotransport properties in 6- and 7-septuple-layer MnBi2Te4, and reveal that both even- and odd-number-layer device can show zero Hall plateau phenomena in zero magnetic field. Importantly, a statistical survey of the optical contrast in more than 200 MnBi2Te4 flakes reveals that the zero Hall plateau in odd-number-layer devices arises from the reduction of the effective thickness during the fabrication, a factor that was rarely noticed in previous studies of 2D materials. Our finding not only provides an explanation to the controversies regarding the discrepancy of the even-odd layer dependent magnetotransport in MnBi2Te4, but also highlights the critical issues concerning the fabrication and characterization of 2D material devices.

cond-mat.mes-hall↗