arXiv subjects

Zhihao Dai

Publications and source records attributed to Zhihao Dai.

5 recordsLinked to original sources

arXiv2026

Switchable Altermagnetism via Spin-Induced Improper Polarization

Enabling reversible spin-splitting switching in stray-field-free altermagnets is promising for spintronic applications, but currently limited to a narrow class of polar materials. We propose a broader approach based on spin-induced improper polarization in nonpolar dual-sublattice magnets. We demonstrate this mechanism in DyFeO3, where the product of nonpolar Fe and Dy spin modes transforms as an induced polar mode. Density functional theory shows that the relative Dy--Fe spin alignment selects the polarization, while the Fe sublattice controls nonrelativistic spin splitting, thus enabling reversible switching. These results establish spin-induced improper polarization as a route to switchable altermagnetism in nonpolar bulk systems.

cond-mat.mtrl-sci↗

arXiv2026

Unified Zero-Shot Time Series Forecasting: A Darts Foundation

Since its initial release in 2020, Darts has become a widely used open-source Python library for time series analysis. A series of foundation models have recently claimed accuracy improvements in zero-shot forecasting, promising a paradigm shift from training custom models to harnessing pre-trained general-purpose forecasters. Foundation models, however, are often released as isolated packages with fragmented interfaces and limited interoperability with common tooling, making joint evaluation and integration within complete pipelines difficult. In Darts, we developed a unified $\texttt{FoundationModel}$ class collection (Chronos-2, TimesFM 2.5, TiRex, PatchTST-FM) that provides standardized, full-cycle forecasting interfaces with minimal external dependencies for integrating foundation models into the ecosystem. Existing Darts pipelines can now use foundation models with only a name change; new pipelines can use them for zero-shot or fine-tuned forecasting, uncertainty estimation, and backtesting, combined with data processing and evaluation tooling, all within a unified framework.

cs.LG↗

arXiv2026

General Theory for Ferroelectric Control of Spin Splitting in Collinear Antiferromagnets

Electrical control of magnetism is crucial for next-generation spintronics. While recent advances have demonstrated ferroelectric switching in two-dimensional magnets, a general design strategy spanning different dimensionalities remains elusive. Here, we develop a group-theoretical framework for achieving ferroelectric control of spin splitting in collinear antiferromagnets, including altermagnets and compensated ferrimagnets. By systematically classifying switching operators through symmetry analysis, we identify a universal pathway for the simultaneous reversal of electric polarization and nonrelativistic spin splitting.We validate this approach in three representative systems: quasi-one-dimensional $(6,14)$ Zigzag graphene nanoribbons, two-dimensional~\ch{Nb3I8}, and three-dimensional altermagnetic~\ch{MnSe2}. Our work establishes a versatile design paradigm for magnetoelectric devices and expands the functional landscape of low-power spintronic materials beyond the low-dimensional limit.

cond-mat.mtrl-sci↗

arXiv2025

General First-Principles Approach to Crystals in Finite Magnetic Fields

We introduce a general first-principles methodology for computing electronic structure in a finite uniform magnetic field which allows for an arbitrary rational magnetic flux and nonlocal pseudopotentials, at a comparable time complexity of conventional plane-wave pseudopotential approaches in zero-field conditions. The versatility of this method is demonstrated through comprehensive applications to both molecular and crystalline systems, including calculations of magnetizabilities, magnetically induced currents, and magnetic energy bands. Furthermore, we provide rigorous proofs of two properties for crystals in uniform magnetic fields: the "strong translational symmetry" and "magnetic bands shift" phenomena.

cond-mat.mtrl-sci↗

arXiv2025

Defect-Charge-Driven 90° Switching in HfO2

Hafnium dioxide (HfO2) is a CMOS-compatible ferroelectric showing both 180° and 90° switching, yet the microscopic nature of the 90° pathway remains unresolved. We show that the 90° rotation pathway, negligible in pristine HfO2, becomes dominant under E// [111] when induced by charged oxygen vacancies. This pathway is more fatigue-resistant than the 180° reversal pathway, while delivering the same polarization change along [111] (2Pr=60 μC/cm^2 ). This charge-driven switching arises from two factors: the crystal geometry of HfO2 and the intrinsic nature of rotational pathways, the latter suggesting a possible general tendency for defect charge to bias rotation over reversal in ferroelectrics. Together these findings reveal a pathway-level origin of fatigue resistance and establish defect charge as a general control parameter for polarization dynamics.

cond-mat.mtrl-sci↗