Discovery of Real-Space Topological Ferroelectricity in Metallic Transition Metal Phosphides
Discovery of Real-Space Topological Ferroelectricity in Metallic Transition Metal Phosphides
复制标题
金属过渡金属磷化物中实空间拓扑铁电性的发现
DOI：
10.1002/adma.202003479
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发表时间：
2020
影响因子：
29.4
通讯作者：
Dunin-Borkowski Rafal E.
中科院分区：
文献类型：
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作者：
Wei Xian-Kui;Bihlmayer Gustav;Zhou Xiaodong;Feng Wanxiang;Kolen'ko Yury V;Xiong Dehua;Liu Lifeng;Bluegel Stefan;Dunin-Borkowski Rafal E.
铁电金属-同时存在铁电性和结构不对称性-挑战传统的看法，因为自由电子屏蔽离子之间的静电力，打破空间反演对称性的驱动力。尽管铁电金属已陆续被发现，但具有金属丰度的拓扑可切换极性物体至今尚未被发现。本文报道了在金属和非中心对称Ni2P中发现的实空间拓扑铁电性。在旋转-反转对称操作的保护下，发现交替堆叠的多面体的平衡极性与元素价态密切耦合，并用定量电子能损失谱验证了这一点。第一性原理计算表明，施加在平面内的压缩应变会产生可调的双线性双阱电位，并在单位细胞尺度上逆转多面体极性。镍离子的双重作用，包括多面体笼内的极性位移和三维键合网络，促进了拓扑极性和金属丰度的共存。此外，可切换的平面内多面体极性产生了自旋-轨道耦合诱导的自旋织构，具有较大的动量依赖自旋分裂。这些发现为探索结构不对称金属体系中拓扑铁电性的价-极性-自旋相关相互作用指明了新的方向。
Ferroelectric metals—with coexisting ferroelectricity and structural asymmetry—challenge traditional perceptions because free electrons screen electrostatic forces between ions, the driving force of breaking the spatial inversion symmetry. Despite ferroelectric metals having been unveiled one after another, topologically switchable polar objects with metallicity have never been identified so far. Here, the discovery of real‐space topological ferroelectricity in metallic and non‐centrosymmetric Ni2P is reported. Protected by the rotation–inversion symmetry operation, it is found that the balanced polarity of alternately stacked polyhedra couples intimately with elemental valence states, which are verified using quantitative electron energy‐loss spectroscopy. First‐principles calculations reveal that an applied in‐plane compressive strain creates a tunable bilinear double‐well potential and reverses the polyhedral polarity on a unit‐cell scale. The dual roles of nickel cations, including polar displacement inside polyhedral cages and a 3D bonding network, facilitate the coexistence of topological polarity with metallicity. In addition, the switchable in‐plane polyhedral polarity gives rise to a spin–orbit‐coupling‐induced spin texture with large momentum‐dependent spin splitting. These findings point out a new direction for exploring valence–polarity–spin correlative interactions via topological ferroelectricity in metallic systems with structural asymmetry.