Evidence of Ferroelectricity in an Antiferromagnetic Vanadium Trichloride Monolayer

Evidence of Ferroelectricity in an Antiferromagnetic Vanadium Trichloride Monolayer

Science Advances 11, eado6538 (2025); arXiv:2404.13513 (2024)

Jinghao Deng#, Deping Guo#, Yao Wen, Shuangzan Lu, Zhengbo Cheng, Zemin Pan, Tao Jian, Yusong Bai, Hui Zhang, Wei Ji*, Jun He*, Chendong Zhang*

Multiferroicity allows magnetism to be controlled using electric fields or vice versa, which has gained tremendous interest in both fundamental research and device applications. A reduced dimensionality of multiferroic materials is highly desired for device miniaturization, but the coexistence of ferroelectricity and magnetism at the two-dimensional limit is still debated. Here, we used a NbSe2 substrate to break both the C3 rotational and inversion symmetries in monolayer VCl3 and thus introduced exceptional in-plane ferroelectricity into a two dimensional magnet. Scanning tunnelling spectroscopy directly visualized ferroelectric domains and manipulated their domain boundaries in monolayer VCl3, where coexisting antiferromagnetic order with canted magnetic moments was verified by vibrating sample magnetometer measurements. Our density functional theory calculations highlight the crucial role that highly directional interfacial Cl–Se interactions play in breaking the symmetries and thus in introducing in-plane ferroelectricity, which was further verified by examining an ML-VCl3/graphene sample. Our work demonstrates an approach to manipulate the ferroelectric states in monolayered magnets through van der Waals interfacial interactions.

研究组合作揭示单层二维材料中磁—电共存新机制

研究组合作揭示单层二维材料中磁—电共存新机制

近日,中国人民大学物理学院季威教授研究组联合武汉大学张晨栋教授等组成联合研究团队,通过理论计算结合实验测量,在单层二维材料三氯化钒(VCl3)中,实现了反铁磁性与铁电性共存,揭示了范德华界面相互作用对磁-电共存的调控机制。相关研究成果以“Evidence of Ferroelectricity in an Antiferromagnetic Vanadium Trichloride Monolayer”为题,于2025年3月5日发表《Science》子刊《Science Advances》[Science Advances 11, eado6538 (2025)]上。

自发对称性破缺是凝聚态物理中的核心现象之一,也是产生极化态的关键机制,与磁性、超导电性、铁电性等密切相关。它还为信息存储和处理提供了原理基础,也是电子信息领域关心的关键科学问题之一。多铁性材料因能同时展现磁性与铁电性,成为低能耗、高密度信息存储和新型电子器件开发的重要候选材料,也为深入理解凝聚态系统中复杂有序态的形成和调控提供了材料平台。传统多铁性材料多以体相形式存在,然而,在二维极限下,热涨落和量子涨落显著,较低的对称性也限制了其自发破缺的可能性,使得磁-电共存面临巨大挑战。尽管最近的研究表明,磁性和铁电性可分别在单层二维材料中独立存在,但单层多铁性(磁电共存)的存在仍缺乏确凿证据。

针对这一挑战,合作团队利用二硒化铌(NbSe2)范德瓦尔斯衬底的强层间电子耦合特性,在磁性VCl3单层中诱导出通过结构与磁性耦合的面内电铁电性。具体地,通过分子束外延生长和扫描隧道显微镜(STM)观测,团队发现VCl3原子结构发生显著畸变,并直接观测到铁电畴壁及能带弯曲现象(图1),测得铁电极化强度约为0.04 μC/cm2,并成功实现了铁电畴翻转。振动样品磁强计(VSM)测量进一步证实VCl3具有反铁磁性,并在16 K温度下发生磁相变。

图1.  在NbSe2衬底上生长的单层VCl3原子结构畸变(A)、铁电畴壁(B)和能带弯曲现象(C,D)。

密度泛函理论计算揭示了具有方向性的Cl–Se界面相互作用在破缺VCl3C3面内旋转对称性、继而诱导面内铁电性中的关键作用。在不具有方向性相互作用的石墨烯—VCl3界面中,单层VCl3并未显著破缺面内旋转对称性,也未展现出面外电极化,印证了具有方向性的界面相互作用在诱导面内铁电性中的重要性。这一成果不仅为二维单层极限下的多铁性材料研究奠定了基础,也初步揭示了旋转对称性破缺与面内电极化之间的深刻联系,还为利用范德华界面相互作用诱导和调控多铁性开辟了新的思路,也为推动新型多功能器件研发提供了原理基础。

图2. 单层VCl3与NbSe2 (A-D)和石墨烯(F-H)衬底界面处的自旋密度分布图(A,F)及差分电荷密度分布的俯视(B,G)和侧视(C,D,H)图。

四川师范大学物理与电子工程学院讲师郭的坪博士(物理学院2024级博士毕业生)和武汉大学邓京昊博士、文耀博士、卢双赞博士为论文的共同第一作者。物理学院季威教授、武汉大学张晨栋教授、武汉大学何军教授为该论文的共同通讯作者。该工作的理论计算部分由郭的坪博士和季威教授完成,实验部分由合作单位完成,并得到了国家自然科学基金、科技部、教育部等的支持。相关计算在中国人民大学计算云平台和物理学院高性能计算实验室完成。

文章链接:Evidence of Ferroelectricity in an Antiferromagnetic Vanadium Trichloride Monolayer | Science Advances

Spatially anisotropic Kondo resonance intertwined with superconducting gap in kagome metal CsV3-xCrxSb5

Spatially anisotropic Kondo resonance intertwined with superconducting gap in kagome metal CsV3-xCrxSb5

Zichen Huang#, Hui Chen#,*, Zhongqin Zhang#, Hao Zhang#, Zhen Zhao, Ruwen Wang, Haitao Yang, Wei Ji*, Ziqiang Wang, Hong-Jun Gao*

The newly-discovered chromium-based kagome metal CsCr3Sb5 has garnered significant interest due to its strong electron correlations, intertwined orders and potential for unconventional superconductivity under high pressure. However, the nature of superconducting and magnetic interactions during the transition from the parent compound CsV3Sb5 to CsCr3Sb5 remains elusive. Here, we report the discovery of spatially anisotropic Kondo resonance which intertwines with the superconducting gap, facilitated by the introduction of magnetic Cr impurities into the kagome superconductor CsV3Sb5. In addition to the gradual suppression of long-ranged charge-density-wave orders, dilute Cr dopants induce local magnetic moments, giving rise to the emergence of Kondo resonances. In addition, the Kondo resonance forms spatially anisotropic ripple-like structures around the Cr dopants, breaking all local mirror symmetries. This anisotropy arises from the antiferromagnetic coupling between itinerant electrons and the Cr-induced spin-up electrons. Remarkably, as the Kondo screening develops, the coherence peak and depth of superconducting gap with finite zero-energy conductance significantly enhances. It indicates that non-superconducting pairs at the Fermi surface in the parent compound participate in the Kondo effect, effectively screening the magnetic moments of Cr dopants while simultaneously enhancing the superfluid density. Our findings pave a unique pathway for exploring the interplay between superconductivity and local magnetic moments in kagome systems.

Luttinger compensated bipolarized magnetic semiconductor

Luttinger compensated bipolarized magnetic semiconductor

Peng-Jie Guo, Xiao-Yao Hou, Ze-Feng Gao, Huan-Cheng Yang, Wei Ji, Zhong-Yi Lu

Altermagnetic materials, with real-space antiferromagnetic arrangement and reciprocal-space anisotropic spin splitting, have attracted much attention. However, the spin splitting is small in most altermagnetic materials, which is a disadvantage to their application in electronic devices. In this study, based on symmetry analysis and the first-principles electronic structure calculations, we predict for the first time two Luttinger compensated bipolarized magnetic semiconductors Mn(CN)2 and Co(CN)2 with isotropic spin splitting as in the ferromagnetic materials. Our further analysis shows that the Luttinger compensated magnetism here depends not only on spin group symmetry, but also on the crystal field splitting and the number of d-orbital electrons. In addition, the polarized charge density indicates that both Mn(CN)2 and Co(CN)2 have the quasi-symmetry T{\tau} , resulting from the crystal field splitting and the number of d-orbital electrons. The Luttinger compensated magnetism not only has the zero total magnetic moment as the antiferromagnetism, but also has the isotropic spin splitting as the ferromagnetism, thus our work not only provides theoretical guidance for searching Luttinger compensated magnetic materials with distinctive properties, but also provides a material basis for the application in spintronic devices.

Efficient energy transfer in a hybrid organic-inorganic van der Waals heterostructure

Efficient energy transfer in a hybrid organic-inorganic van der Waals heterostructure

Xiaoqing Chen#, Huijuan Zhao#, Ruixiang Fei, Chun Huang, Jingsi Qiao, Cheng Sun, Haiming Zhu, Li Zhan, Zehua Hu, Songlin Li, Li Yang, Zemin Tang, Lianhui Wang, Yi Shi, Wei Ji, Jian-Bin Xu, Li Gao*, Xuetao Gan* & Xinran Wang*

Two-dimensional materials offer strong light-matter interaction and design flexibility beyond conventional bulk semiconductors, but an intrinsic limit is the low absorption imposed by the atomic thickness. A long-sought-after goal is to achieve complementary absorption enhancement through energy transfer (ET) to break this intrinsic limit. However, it is found challenging due to the competing charge transfer process and lack of resonance in exciton states. Here, we report highly efficient energy transfer (ET) in a 2D hybrid organic-inorganic heterostructure (HOIST) of Me-PTCDI/WS2. Resonant ET is observed leading to enhanced WS2 PL by as much as 124 times. We identify Dexter exchange between the Frenkel state in donor and an excited 2s state in acceptor as the main ET mechanism, as supported by density functional theory calculations. We further demonstrate ET-enhanced phototransistor devices with enhanced responsivity by nearly 1000 times without sacrificing the response time. Our results expand the understanding of inter-layer relaxation.