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稳定且显著的谷极化效应是谷自由度在谷电子器件中应用的关键。基于第一性原理计算，本文发现单层交错磁体V2Se2O在单轴应变下的谷极化效应关联磁性原子V之间的净磁矩，提出了实现巨大谷极化效应的两种策略。其一，利用Cr原子替换V2Se2O单层中的一个V原子形成亚铁磁单层VCrSe2O，使磁性原子之间的净磁矩足够大，实现巨大的谷极化效应。通过在a轴或b轴方向施加单轴应变能显著地提升谷极化值，且谷极化值与磁性原子之间的净磁矩呈近线性关系。其二，构建V2Se2O单层和α-SnO单层的范德华异质结，镜面对称破缺的堆垛方式使V原子之间出现净磁矩，从而实现显著的谷极化效应。通过压缩异质结的层间距离可以引起V原子之间净磁矩的增加，能将谷极化值提升至近400meV。本工作在单层交错磁体的基础上提出了实现巨大谷极化的两种策略，为基于交错磁体构筑的亚铁磁单层和异质结材料在谷电子学领域的应用提供理论指导。Stable and remarkable valley polarization effect is the key to utilizing valley degree of freedom in valleytronic devices. Recently, a novel collinear magnetic material known as altermagnet, distinct from ferromagnets and antiferromagnets, has attracted widespread attention. Theoretical studies have revealed that the monolayer altermagnet V2Se2O exhibits spin-valley locking induced by crystal symmetry rather than conventional time-reversal symmetry. Uniaxial strain can break the corresponding crystal symmetry, leading to a remarkable non-relativistic valley polarization effect. Therefore, beyond uniaxial strain, are there alternative strategies to break the crystal symmetry in altermagnets and achieve remarkable valley polarization? Based on firstprinciples calculations and symmetry analysis, we reveal that valley polarization effect in monolayer V2Se2O altermagnet is correlated with the net magnetic moment between magnetic atoms V under uniaxial strain, proposing two strategies for achieving giant valley polarization effect. Firstly, substituting one V atom in V2Se2O with Cr to construct a ferrimagnetic monolayer VCrSe2O enhances the net magnetic moment between magnetic atoms, thereby realizing giant valley polarization effect. Applying uniaxial strain along either the a-axis or b-axis significantly increases the value of valley polarization which exhibits a nearly linear relationship with the net magnetic moments between the magnetic atoms. Secondly, constructing a van der Waals heterostructure composed of V2Se2O and α-SnO monolayers breaks mirror symmetry, as a result, inducing a net magnetic moment, which in turn induces remarkable valley polarization effect. Compressing the interlayer distance of the heterostructure enables an increment of the net magnetic moment between V atoms, enhancing the value of valley polarization to nearly 400 meV. This work reveals that valley polarization in monolayer altermagnets is correlated with the net magnetic moment between magnetic atoms. Then, we propose two strategies to achieve giant valley polarization based on monolayer altermagnets, providing theoretical guidance for the potential applications of ferrimagnetic monolayers and heterostructures constructed from altermagnets in valleytronics.
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Keywords:
- Valley degree of freedom /
- Monolayer altermagnets /
- Valley polarization /
- Ferrimagnetic /
- Van der Waals heterostructure
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