arXiv subjects

Zhongjun Li

Publications and source records attributed to Zhongjun Li.

8 recordsLinked to original sources

arXiv2026

Cross-Layer Anomalous Hall Transport driven by N\'eel-Vector rotating in the Altermagnet candidate V2Te2O

In van der Waals (vdW) materials, weak interlayer coupling generally suppresses vertical dispersion, reinforcing the conventional paradigm that in-plane transport dominates over cross-layer channels. Here, using first-principles calculations and magnetic symmetry analyses, we uncover a giant, symmetry-unlocked cross-layer anomalous Hall conductivity (AHC) in the vdW altermagnet V2Te2O. In the magnetic ground state with Neel vector N//z, horizontal mirror symmetry protects a spin-polarized nodal chain near the Fermi level and strictly enforces zero anomalous Hall response. Tilting the Neel vector explicitly breaks this mirror protection, allowing spin-orbit coupling to gap the nodal chain and activate a sharp cross-layer Hall response. When the Neel vector is rotated into the in-plane configuration (N//x), cross-layer orbital hybridization generates intensive Berry curvature hotspots, boosting the cross-layer component of AHC {\sigma}_{yz} to approximately 255 S/cm, which exceeds in-plane component {\sigma}_{xy} by nearly two orders of magnitude. Furthermore, varying the azimuthal angle systematically redistributes the anomalous Hall response, enabling full directional control of transverse transport. Our findings demonstrate a highly sensitive cross-layer anomalous Hall switch activated by low-barrier spin canting, offering promising avenues for directional tensor selection and low-power multi-axial vdW spintronics.

cond-mat.mtrl-sci↗

arXiv2026

Spontaneous spin splitting and tunable valley polarization in a two-dimensional fully compensated ferrimagnet

Materials with controllable valley polarization and anomalous valley Hall (AVH) effect are highly desired in valleytronic applications. While current AVH studies primarily focus on ferromagnetic materials, two-dimensional (2D) antiferromagnets are more attractive for valleytronics since they possess zero net magnetization, negligible stray fields, and ultrafast spin dynamics. Nevertheless, the joint space-inversion and time-reversal ($PT$) symmetry in conventional collinear antiferromagnets prohibits the occurrence of AVH response. The recently proposed fully compensated ferrimagnets break $PT$ symmetry, and the spin-opposite sublattices are not related by crystal symmetry, providing a natural platform for the coexistence of spontaneous spin splitting, valley polarization, and anomalous-Hall compatible symmetry. Herein, we demonstrate that such compensated ferrimagnetism can be realized in a Janus Mn$_{2}$BrI monolayer, with a N\'{e}el temperature above room temperature. Spontaneous spin splitting is observed due to the built-in layer-dependent electrostatic potential. When SOC is considered, valley polarization emerges for an out-of-plane N\'{e}el vector. Moreover, proper hole doping stabilizes the perpendicular magnetic anisotropy and the two valleys exhibit markedly different Berry curvatures, thereby making AHE responses allowed. Furthermore, the valence band extrema of Mn$_{2}$BrI monolayer can be effectively tuned by external biaxial strain and giant piezomagnetism can be achieved. Our results identify Janus Mn$_{2}$BrI monolayer as a promising fully compensated ferrimagnetic platform for 2D valleytronics and spintronics.

cond-mat.mtrl-sci↗

arXiv2026

Strain Engineering of Intrinsic Anomalous Hall and Nernst Effects in Altermagnetic MnTe at Realistic Doping Levels

Hexagonal MnTe has emerged as a prototypical g-wave altermagnet, hosting time-reversal symmetry breaking in momentum space despite a vanishing net magnetization. While this symmetry breaking theoretically allows for an intrinsic anomalous Hall effect, experimentally observed signals have remained weak. In this work, we investigate the origin of this suppression and demonstrate a strategy to amplify anomalous transport responses within the experimentally accessible doping regime. Using a $\bm{k}\cdot\bm{p}$ effective model, we reveal that near the valence band maximum, which corresponds to the energy window relevant for typical hole doping ($\sim10^{19}cm^{-3}$), the intrinsic Hall effect is suppressed due to a symmetry-enforced cancellation of opposing Berry curvature contributions. We propose that breaking the crystalline symmetry via volume-conserving biaxial strain lifts this cancellation, resulting in a significant enhancement of the anomalous Hall conductivity by orders of magnitude. This strain-induced Fermi surface distortion also amplifies the anomalous Nernst effect. Furthermore, the analysis of the spin texture confirms that these strain-enabled anomalous transport signatures emerge while preserving the zero net magnetization.

cond-mat.mtrl-sci↗

arXiv2025

Entropy-Controlled Intrinsic Motivation Reinforcement Learning for Quadruped Robot Locomotion in Complex Terrains

Learning is the basis of both biological and artificial systems when it comes to mimicking intelligent behaviors. From the classical PPO (Proximal Policy Optimization), there is a series of deep reinforcement learning algorithms which are widely used in training locomotion policies for quadrupedal robots because of their stability and sample efficiency. However, among all these variants, experiments and simulations often converge prematurely, leading to suboptimal locomotion and reduced task performance. Therefore, in this paper, we introduce Entropy-Controlled Intrinsic Motivation (ECIM), an entropy-based reinforcement learning algorithm in contrast with the PPO series, that can reduce premature convergence by combining intrinsic motivation with adaptive exploration. For experiments, in order to parallel with other baselines, we chose to apply it in Isaac Gym across six terrain categories: upward slopes, downward slopes, uneven rough terrain, ascending stairs, descending stairs, and flat ground as widely used. For comparison, our experiments consistently achieve better performance: task rewards increase by 4--12%, peak body pitch oscillation is reduced by 23--29%, joint acceleration decreases by 20--32%, and joint torque consumption declines by 11--20%. Overall, our model ECIM, by combining entropy control and intrinsic motivation control, achieves better results in stability across different terrains for quadrupedal locomotion, and at the same time reduces energetic cost and makes it a practical choice for complex robotic control tasks.

cs.RO↗

arXiv2025

Uni2D: A Universal Machine Learning Interatomic Potential for Two-Dimensional Materials

Accurate interatomic potentials (IAPs) are essential for modeling the potential energy surfaces (PES) that govern atomic interactions in materials. However, most existing IAPs are developed for bulk materials and often struggle to accurately and efficiently capture the diverse chemical environments of two-dimensional (2D) materials, which limits large-scale simulation and design of emerging 2D systems. To address this challenge, we develop Uni2D, an interatomic potential tailored for 2D materials. The Uni2D model is trained on a dataset comprising approximately 327,000 structure-energy-force-stress mappings derived from about 20,000 distinct 2D materials, covering 89 chemical elements. The model demonstrates reliable predictive performance for energies, forces, and stresses, and demonstrates quantitatively robust accuracy in tasks such as structural relaxation, equation-of-state calculations, and molecular dynamics simulations, making the model suitable for high-throughput screening of 2D materials. For derived properties, including elastic properties, lattice dynamics, and other screening-related metrics, the model provides qualitative to semi-quantitative predictions that remain useful for trend analysis and preliminary evaluation. To enhance usability, we further introduce an intelligent agent powered by a large language model (LLM), enabling automated workflows and natural language interaction for 2D materials simulations. Our work provides an efficient and accessible framework for high-throughput screening and computational exploration of 2D materials.

cond-mat.mtrl-sci↗

arXiv2025

High-throughput calculations of two-dimensional auxetic $M_4X_8$ with magnetism, electrocatalysis, and alkali metal battery applications

Two-dimensional (2D) materials with multifunctional properties, such as negative Poisson's ratio (NPR), magnetism, catalysis, and energy storage capabilities, are of significant interest for advanced applications in flexible electronics, spintronics, catalysis, and lithium-ion batteries. However, the discovery of such materials, particularly in low-dimensional forms, remains a challenge. In this study, we perform high-throughput density-functional theory (DFT) calculations to explore a new class of 2D V-shaped monolayers with remarkable physicochemical properties. Among 18 stable $M_4X_8$ (M = transition metal; X = halogen) compounds, we identify 9 auxetic monolayers, with \ce{Pd4I8} standing out for its exceptionally high NPR of -0.798. Notably, 4 of these materials exhibit half semiconductor properties, while 5 others are bipolar magnetic semiconductors, offering a unique combination of electronic and magnetic behavior. Additionally, these materials demonstrate promising catalytic activity for hydrogen and oxygen evolution reactions (HER/OER) and show potential as anodes for rechargeable metal-ion batteries, particularly in alkali-ion systems. This work not only expands the family of 2D NPR materials but also introduces new candidates with multifunctional capabilities for a wide range of applications in nanoelectronics, catalysis, and energy storage.

cond-mat.mes-hall↗

arXiv2024

High-throughput Screening of Ferrimagnetic Semiconductors With Ultrahigh N$\acute{e}$el Temperature

Ferrimagnetic semiconductors, integrated with net magnetization, antiferromagnetic coupling and semi-conductivity, have constructed an ideal platform for spintronics. For practical applications, achieving high N$\acute{e}$el temperatures ($T_{\mathrm{N}}$) is very desirable, but remains a significant challenge. Here, via high-throughput density-functional-theory calculations, we identify 19 intrinsic ferrimagnetic semiconductor candidates from nearly 44,000 structures in the Materials Project database, including 10 ferrimagnetic bipolar magnetic semiconductors (BMS) and 9 ferrimagnetic half semiconductors (HSC). Notably, the BMS \ce{NaFe5O8} possesses a high $T_{\mathrm{N}}$ of 768 K. By element substitutions, we obtain an HSC \ce{NaFe5S8} with a $T_{\mathrm{N}}$ of 957 K and a BMS \ce{LiFe5O8} with a $T_{\mathrm{N}}$ reaching 1059 K. Our results pave a promising avenue toward the development of ferrimagnetic spintronics at ambient temperature.

cond-mat.mtrl-sci↗

arXiv2008

Hyperconjugative Effect on the Electronic Wavefunctions of Ethanol

Hyperconjugation is a basic conception of chemistry. Its straightforward effect is exhibited by the spatial delocalization characteristics of the electron density distributions or wavefunctions. Such effects on the electron wavefunctions of the highest-occupied molecular orbitals (HOMO) of two ethanol conformers are demonstrated with electron momentum spectroscopy together with natural bond orbital analyses, exhibiting the distinctly different symmetries of the HOMO wavefunctions in momentum space.

physics.chem-ph↗