Evidence for a single-layer van der Waals multiferroic
Evidence for a single-layer van der Waals multiferroic
复制标题
DOI：
10.1038/s41586-021-04337-x
复制
发表时间：
2022-02-24
期刊：
影响因子：
64.8
通讯作者：
Comin, Riccardo
中科院分区：
文献类型：
--
作者：
Song, Qian;Occhialini, Connor A.;Comin, Riccardo
多铁性材料由于其优异的静态（1-3）和动态（4-6）磁电性能而引起了人们的广泛兴趣。特别是，II型多铁性表现出反转对称性破坏磁序，通过各种机制直接诱导铁电极化，如自旋电流或逆Dzyaloshinskiiii-Moriya效应（3，7）。磁序参数和偶极序参数之间的这种内在耦合导致高强度磁电效应（3，8）。长期以来，人们一直在寻找具有这种固有多铁性的二维材料，以利用纳米电子器件中的磁电耦合（1，9，10）。在这里，我们报告的发现，在一个单一的原子层的过渡金属为基础的货车德瓦尔斯材料NiI 2的II型多铁性秩序。NiI 2的多铁性状态的特征在于具有给定旋向的适当螺旋自旋螺旋，其耦合到电荷自由度以产生手性控制的电极化。我们使用圆二色性拉曼测量直接探测的磁手征基态和它的电磁振子模式起源于动态磁电耦合。结合双折射和二次谐波产生测量与理论建模和模拟，我们检测到一个高度各向异性的电子状态，同时打破三重旋转和反转对称性，并支持极序。的光学签名作为温度和层数的函数的演变令人惊讶地揭示了一个有序的磁极状态，持续到单层NiI 2的磁极限。这些观测建立了NiI 2和过渡金属二卤化物作为一个新的平台，研究新兴的多铁性现象，手性磁纹理和铁电性在二维limit.Multiple互补的光学签名确认铁电性和反转对称性破坏磁秩序的持久性下降到单层NiI 2，引入到货车德瓦耳斯材料领域的第二类多铁性物理。
Multiferroic materials have attracted wide interest because of their exceptional static(1-3) and dynamical(4-6) magnetoelectric properties. In particular, type-II multiferroics exhibit an inversion-symmetry-breaking magnetic order that directly induces ferroelectric polarization through various mechanisms, such as the spin-current or the inverse Dzyaloshinskii-Moriya effect(3,7). This intrinsic coupling between the magnetic and dipolar order parameters results in high-strength magnetoelectric effects(3,8). Two-dimensional materials possessing such intrinsic multiferroic properties have been long sought for to enable the harnessing of magnetoelectric coupling in nanoelectronic devices(1,9,10). Here we report the discovery of type-II multiferroic order in a single atomic layer of the transition-metal-based van der Waals material NiI2. The multiferroic state of NiI2 is characterized by a proper-screw spin helix with given handedness, which couples to the charge degrees of freedom to produce a chirality-controlled electrical polarization. We use circular dichroic Raman measurements to directly probe the magneto-chiral ground state and its electromagnon modes originating from dynamic magnetoelectric coupling. Combining birefringence and second-harmonic-generation measurements with theoretical modelling and simulations, we detect a highly anisotropic electronic state that simultaneously breaks three-fold rotational and inversion symmetry, and supports polar order. The evolution of the optical signatures as a function of temperature and layer number surprisingly reveals an ordered magnetic polar state that persists down to the ultrathin limit of monolayer NiI2. These observations establish NiI2 and transition metal dihalides as a new platform for studying emergent multiferroic phenomena, chiral magnetic textures and ferroelectricity in the two-dimensional limit.Multiple complementary optical signatures confirm the persistence of ferroelectricity and inversion-symmetry-breaking magnetic order down to monolayer NiI2, introducing the physics of type-II multiferroics into the area of van der Waals materials.