博士生陈俊荧同学在国际顶级物理学期刊Nature Physics上发表论文

      近日，课题组成员陈俊荧同学在刘老师的指导下，以第一作者在国际物理学顶级期刊《自然物理》(Nature Physics)上发表题为“Altermagnetism in Twisted van der Waals Homostructures”(转角 CrPS₄ 范德华同质结中交错磁性的实验观测)的实验论文。

图：转角 CrPS₄ 范德华同质结中交错磁性的实验观测

     磁性在经典意义上主要分为铁磁性和反铁磁性，是凝聚态物理学的重要基石，并支撑着数据存储、自旋电子器件和磁传感等众多现代技术的发展。铁磁体具有平行的自旋排列，并表现出净磁矩；而反铁磁体则具有反平行的自旋排列，其磁矩在宏观尺度上相互抵消。尽管铁磁性和反铁磁性具有重要的技术应用价值，但二者均存在内在局限性：铁磁体容易受到杂散磁场引起的不稳定性影响，且磁性翻转速度受到限制；反铁磁体则由于缺乏净磁矩，使其难以通过外部磁场实现有效操控。

    近年来提出的一类新型磁序——交错磁性(altermagnetism)——架起了铁磁性与反铁磁性之间的桥梁。交错磁体兼具补偿性的反平行自旋排列和动量空间中的有限自旋劈裂，从而能够在无净磁化的情况下实现自旋极化输运。这种非常规磁性态已经在多种三维(3D)化合物中获得理论和实验上的验证，包括通过角分辨光电子能谱(ARPES)和软 X 射线角分辨光电子能谱观测到的自旋劈裂能带、反常霍尔效应、X 射线磁圆二色性，以及类似铁磁体的磁光克尔响应。这些研究结果表明，交错磁性是一种区别于传统铁磁性和反铁磁性的独特量子态，并为自旋电子学的发展展现出重要潜力。

    然而，迄今为止，交错磁性的实验实现主要局限于三维体系，而具有更高可调控性并能够进一步集成到范德华(vdW)异质结构中的二维(2D)交错磁体仍鲜有实验探索。从理论上看，在范德华磁性材料中引入层间扭转，可以诱导面内二重旋转对称性，并通过对称性调控的自旋–轨道耦合和交换相互作用产生交错磁态。 这一策略为二维交错磁体的设计提供了一条灵活而有效的途径，同时也有望拓展下一代自旋电子器件架构的材料体系。然而，对于这种由层间扭转诱导的交错磁性的直接实验观测，迄今仍未实现。

    在本工作中，我们首次在正交扭转的 CrPS₄/CrPS₄ 同质结构(90°-CrPS₄/CrPS₄)中实现了交错磁性的实验观测。磁光光谱测量揭示了圆偏振度(degree of circular polarization, DOCP)随磁场呈现类似铁磁性的依赖关系：当磁场从 −9 T 扫描至 9 T 时，在 σ⁺ 和 σ⁻ 激发下，DOCP 表现出方向相反的变化。值得注意的是，我们观察到显著的塞曼劈裂(Zeeman splitting)，而这一特征在铁磁和反铁磁 CrPS₄ 中均不存在，表明该体系具有不同寻常的磁基态。第一性原理计算进一步表明，这种较大的塞曼劈裂源于显著的自旋劈裂能带，从而验证了 90° 扭转体系中交错磁性的产生。

      此外，互补的偏振拉曼光谱测量发现了由层间耦合诱导的声子模式劈裂，这一现象可归因于顶层与底层之间的交错磁相互作用。我们的研究建立了一种通过对称性工程实现二维范德华材料交错磁性的新途径，并提供了一个无需净磁化即可探索自旋极化物理现象的有力实验平台。该工作为基于交错磁序设计低耗散、高速自旋电子器件和存储器件开辟了新的方向。

文章链接：https://www.nature.com/articles/s41567-026-03440-y

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Twist Engineering Creates Altermagnetism in van der Waals Homostructures

Central South University researchers demonstrate a symmetry-engineered route to an unconventional magnetic state in orthogonally twisted CrPS₄

Researchers from Central South University, in collaboration with scientists from the University of Sydney, the Institute of Physics of the Chinese Academy of Sciences, the University of Chinese Academy of Sciences, and Songshan Lake Materials Laboratory, have demonstrated altermagnetism in an orthogonally twisted van der Waals homostructure. The work reveals that simply rotating two antiferromagnetic CrPS₄ crystals by 90° can reorganize magnetic symmetry and produce a compensated magnetic state with pronounced spin splitting—a defining characteristic of altermagnetism. 

The study, entitled “Altermagnetism in Twisted van der Waals Homostructures,” was led by Prof. Yanping Liu at the Institute of Quantum Physics, School of Physics, Central South University. Junying Chen and Xing Xie are co-first authors of the work. 

A new route beyond conventional ferro- and antiferromagnetism

For decades, magnetic materials have been broadly classified as ferromagnets or antiferromagnets. Ferromagnets possess a net magnetization and are readily manipulated, but their stray magnetic fields can hinder device miniaturization. Antiferromagnets, by contrast, have compensated magnetic moments and negligible stray fields, but their magnetic states are generally more difficult to detect and control.

Altermagnetism has recently emerged as a third form of magnetic order that combines important characteristics of both. In an altermagnet, oppositely oriented magnetic moments compensate macroscopically, as in an antiferromagnet, while the electronic bands remain strongly spin split, resembling an important electronic feature of ferromagnets. Such a combination could enable spin-polarized electronic phenomena without requiring a macroscopic magnetization. 

Although altermagnetism has been explored in several three-dimensional materials, realizing and controlling it in two-dimensional van der Waals systems remains a major challenge. Theory has suggested that relative rotation between magnetic layers could modify crystal and magnetic symmetries sufficiently to create altermagnetic states, but direct experimental evidence in twisted van der Waals structures has remained elusive. 

Creating altermagnetism by a 90° twist

The researchers addressed this challenge using CrPS₄, a layered magnetic semiconductor exhibiting A-type antiferromagnetic order below a Néel temperature of approximately 38 K. They fabricated CrPS₄/CrPS₄ homostructures using a tear-and-stack approach and rotated the two constituent crystals by approximately 90°.

This orthogonal stacking geometry makes the magnetic chains of the upper and lower CrPS₄ layers mutually perpendicular. As a result, the system retains compensated magnetic order while the opposite spin sublattices become connected through rotational symmetry—the essential symmetry condition required for altermagnetism. 

Magneto-optical measurements provide a key experimental signature of this reconstructed magnetic state. In conventional even-layer antiferromagnetic CrPS₄, the circularly polarized photoluminescence follows the characteristic response of its antiferromagnetic configuration. The orthogonally twisted structure, however, displays a markedly different helicity-dependent magnetic-field response, indicating that the 90° rotation fundamentally changes the magnetic symmetry.

Most notably, the 90°-twisted structure exhibits a pronounced Zeeman splitting of approximately 2 meV at 9 T, corresponding to an effective g-factor of about −3.4. Such splitting is negligible in the ferromagnetic and antiferromagnetic CrPS₄ reference structures studied under comparable conditions. The combination of compensated magnetic order, unconventional circular-polarization response and substantial spin splitting therefore distinguishes the twisted structure from conventional ferro- and antiferromagnetic CrPS₄. 

Raman spectroscopy reveals a lattice fingerprint of the twisted magnetic state

The team additionally discovered a striking phononic signature associated with the orthogonally twisted configuration.

Polarization-resolved Raman spectroscopy reveals splitting of the characteristic A₆ and B₆ phonon modes in the symmetric 90°-4L/4L CrPS₄ structure. The A₆ and B₆ modes split by approximately 3.5 cm⁻¹ and 2.6 cm⁻¹, respectively, whereas such behavior is absent in the corresponding small-angle and asymmetric structures.

Detailed polarization analysis further shows that the two split components originate separately from the upper and lower CrPS₄ layers. Their polarization axes remain approximately orthogonal, reflecting the 90° crystallographic rotation. These observations point to an unusual, symmetry-modified interlayer coupling that acts differently on phonons in the two constituent layers. 

The result is particularly important because it suggests that lattice vibrations can provide an additional optical fingerprint of altermagnetic order, opening possibilities for probing the coupling between spin, lattice and interlayer degrees of freedom in twisted magnetic materials.

First-principles calculations reveal the microscopic origin

First-principles calculations further support the experimental observations. Conventional bilayer CrPS₄ exhibits spin-degenerate electronic bands in its compensated antiferromagnetic configuration. In contrast, the 90°-twisted structure develops pronounced spin-split bands.

The calculations reveal that spin-up and spin-down wavefunctions are preferentially localized in different CrPS₄ layers, while the corresponding magnetic chains are related through a 90° rotational symmetry. This coexistence of compensated magnetic order and finite momentum-dependent spin splitting constitutes the central electronic signature of the altermagnetic state. 

Together, the magneto-optical experiments, Zeeman splitting, polarization-resolved Raman spectroscopy and first-principles calculations provide mutually complementary evidence that twist engineering can transform a conventional layered antiferromagnet into an altermagnetic quantum system. The manuscript summarizes this as experimental evidence for altermagnetism in a twisted van der Waals material. 

Twist angle becomes a new knob for magnetic quantum states

Beyond CrPS₄ itself, the work demonstrates a broader concept: interlayer rotation can serve as a symmetry-engineering tool for creating magnetic phases that are absent in naturally stacked materials.

This strategy could potentially be extended to other layered antiferromagnets, while combining twist angle with layer thickness, strain, electrostatic gating and interfacial coupling could offer further control over momentum-dependent spin splitting. The ability to generate compensated magnetic states with finite spin polarization may ultimately benefit low-stray-field, high-speed and energy-efficient spintronic, memory and quantum-information technologies. 

The study was conceived and designed by Yanping Liu. Optical measurements were carried out by Junying Chen, Shaofei Li and Siyu Zhang, while Xing Xie and Jian-Tao Wang performed and analyzed the first-principles calculations. The research received support from the National Natural Science Foundation of China, the Innovation Programme for Quantum Science and Technology, the Australian Research Council and other research programs.