S. Ducharme, V. Fridkin, R. Gaynutdinov, M. Minnekaev, A. Tolstikhina, A. Zenkevich
Switching kinetics in ultrathin epitaxial BaTiO3 films confirms the existence of the homogeneous switching (without domains) in ultrathin ferroelectric films. We suppose that the homogeneous switching in ultrathin films is a common phenomenon for all ferroelectric materials.
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Switchable Topological Polar Textures in Freestanding Ultrathin Ferroelectric Oxides
研究揭示自由悬挂超薄铁电层存在多种极性态，通过电场可逆控制其复杂极性状态，为未来铁电器件应用提供新途径。
Against expectations, robust switchable ferroelectricity has been recently observed in ultrathin (1 nm) ferroelectric films exposed to air [V. Garcia $et$ $al.$, Nature {\bf 460}, 81 (2009)]. Based on first-principles calculations, we show that the system does not polarize unless charged defects or adsorbates form at the surface. We propose electrochemical processes as the most likely origin of this charge. The ferroelectric polarization of the film adapts to the bound charge generated on its surface by redox processes when poling the film. This, in turn, alters the band alignment at the botto…
Low-voltage Ferroelectric Field-Effect Transistors with Ultrathin Aluminum Scandium Nitride and 2D channels
该研究在超薄AlScN铁电薄膜上制备MoS2单层沟道FeFET，通过减薄铁电层将栅极电压降至3V以下，并系统分析厚度、制备方法和环境对磁滞行为的影响，为低功耗CMOS兼容存储计算器件提供优化路径。
Controlling the polarization switching in the ferroelectric nanocrystals, nanowires and nanodots has an inherent specificity related to the emergence of depolarization field that is associated with the spontaneous polarization. This field splits the finite-size ferroelectric sample into polarization domains. Here, based on 3D numerical simulations, we study the formation of 180$^{\circ }$ polarization domains in a nanoplatelet, made of uniaxial ferroelectric material, and show that in addition to the polarized monodomain state, the multidomain structures, notably of stripe and cylindrical shap…
Optical detection of the sliding ferroelectric switching in hBN with a WSe2 monolayer
本研究利用相邻WSe2单层通过光学手段检测hBN中的滑移铁电开关，实现了二维铁电体与半导体的动态耦合，为非破坏性局域光学探测及非易失性存储应用提供了新途径。
Domain wall migration-mediated ferroelectric switching and Rashba effect tuning in GeTe thin films
本研究提出GeTe薄膜中畴壁迁移介导铁电翻转的机制，发现其能量势垒为66.8 meV/nm²，并证实该过程可调控由相反电极化层竞争产生的净Rashba效应，为GeTe器件设计奠定基础。
Bulk LiOsO3 was experimentally identified as a "ferroelectric" metal where polar distortions coexist with metallicity [Shi et al., Nature Materials 12, 1024 (2013)]. It is generally believed that polar displacements in a "ferroelectric" metal cannot be switched by an external electric field. Here, via comprehensive density functional theory calculations, we demonstrate that a two-unit-cell-thick LiOsO3 thin film exhibits a ferroelectric ground state having an out-of-plane electric dipole moment that can be switched by an external electric field. Moreover, its dipole moment-versus-electric-fiel…
Orbital torque and efficient magnetization switching using ultrathin Co|Al light-metal interfaces: Experiments and modeling
本研究通过实验与建模探讨了超薄Co|Al轻金属界面在轨道扭矩和高效磁化翻转中的作用，揭示了轨道极化生成的关键机制。
We show that the spin-orbit torque induced magnetization switching in nanomagnets presenting Dzyaloshinskii-Moriya (DMI) interaction is governed by a chiral domain nucleation at the edges. The nucleation is induced by the DMI and the applied in-plane magnetic field followed by domain wall propagation. Our micromagnetic simulations show that the DC switching current can be defined as the edge nucleation current, which decreases strongly with increasing amplitude of the DMI. This description allows us to build a simple analytical model to quantitatively predict the switching current. We find tha…
We demonstrate the feasibility of multilevel recording in Pt/Bi(1-d)FeO3/SrRuO3 capacitors using the ferroelectric resistive switching phenomenon exhibited by the Pt/Bi(1-d)FeO3 interface. A tunable population of up and down ferroelectric domains able to modulate the Schottky barrier height at the Pt/Bi(1-d)FeO3 interface can be achieved by means of either a collection of SET/RESET voltages or current compliances. This programming scheme gives rise to well defined resistance states, which form the basis for a multilevel storage nonvolatile memory.
The ferroelectric polarization switching in ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) in the HZO/Al2O3 ferroelectric/dielectric stack is investigated systematically by capacitance-voltage and polarization-voltage measurements. The thickness of dielectric layer is found to have a determinant impact on the ferroelectric polarization switching of ferroelectric HZO. A suppression of ferroelectricity is observed with thick dielectric layer. In the gate stacks with thin dielectric layers, a full polarization switching of the ferroelectric layer is found possible by the proposed leaka…
Polarization switching in sliding ferroelectrics: the roles of fluctuation and domain wall
本文利用 \textit{ab initio} 计算研究 $h$-BN 双层的滑动铁电极化翻转动力学，发现非对角 Born 有效电荷驱动垂直离子运动，且面内对称性破缺和畴壁蠕动是翻转的关键因素。
The local hysteresis loop obtained by switching spectroscopy piezoresponse force microscopy (SS-PFM) is usually regarded as a typical signature of ferroelectric switching. However, such hysteresis loops were also observed in a broad variety of non-ferroelectric materials in the past several years, which casts doubts on the viewpoint that the local hysteresis loops in SS-PFM originate from ferroelectricity. Therefore, it is crucial to explore the mechanism of local hysteresis loops obtained in SS-PFM testing. Here we proposed that non-ferroelectric materials can also exhibit amplitude butterfly…
Semiconducting ferroelectric materials with low energy polarisation switching offer a platform for next-generation electronics such as ferroelectric field-effect transistors. Ferroelectric domains at symmetry-broken interfaces of transition metal dichalcogenide films provide an opportunity to combine the potential of semiconducting ferroelectrics with the design flexibility of two-dimensional material devices. Here, local control of ferroelectric domains in a marginally twisted WS2 bilayer is demonstrated with a scanning tunneling microscope at room temperature, and their observed reversible e…
Resolving Polarization Switching Pathways of Sliding Ferroelectricity in Trilayer 3R-MoS2
本研究利用光学技术和层分辨激子响应，揭示三层 3R-MoS2 中界面钉扎畴壁依次释放所决定的多条极化翻转路径。
Ultralow-pressure mechanical-motion switching of ferroelectric polarization
针对机械法切换铁电极化需高压的问题，提出利用摩擦电效应驱动α-In₂Se₃铁电忆阻器极化反转的方法，实现约10 kPa超低压甚至触觉触发的多级电阻态与神经形态应力系统，为触觉铁电器件提供新策略。
Ferroelectric switching control of spin current in graphene proximitized by In$_2$Se$_3$
铁电开关调控石墨烯中近邻的自旋电流，通过计算揭示其自旋纹理特性，为自旋电子器件发展提供新方法。
Proton-Transfer Ferroelectrics with Exceptional Switching Endurance
本研究通过低温度沉积与限制结晶工艺制备高结晶度的2-甲基苯并咪唑薄膜，展现出优异的开关耐久性，其质子转移机制与氢键链相关，且在无工程化结构下实现优于聚合物铁电材料的性能。
The ability to switch between distinct states of polarization comprises the defining property of ferroelectrics. However, the microscopic mechanism responsible for switching is not well understood and theoretical estimates based on coherent monodomain switching typically overestimate experimentally determined coercive fields by orders of magnitude. In this work we present a detailed first principles characterization of domain walls (DWs) in two-dimensional ferroelectric GeS, GeSe, SnS and SnSe. In particular, we calculate the formation energies and migration barriers for 180 and 90 DWs, and th…
Shear-Mode Raman Imaging of Ferroelectric Switching in Multilayer 3$R$-MoS$_2$
利用剪切模式拉曼成像技术研究多层3$R$-MoS$_2$的铁电开关行为，发现不同机械分割区域具有独立响应路径，部分极化终态表明域墙可在特定层对之间存在，产生部分堆叠变换， dwell时间变化表明钉扎位点对动态有显著影响，二次谐波生成测量进一步揭示了三个特征样品边界和域墙取向，包括近锯齿-臂chair双分界线的普遍手性方向。
Ferroelectric domain switching in c-axis-oriented epitaxial Pb(Zr$_{0.2}$Ti$_{0.8}$)O$_3$ thin films was studied using biased scanning probe microscopy tips. While linear and logarithmic dependence of domain size on tip bias and writing time, respectively, are well known, we report an additional linear dependence on relative humidity in the 28-65% range. We map out the switched domain size as a function of both the tip bias and the applied pulse time and describe a growth-limited regime for very short pulses and a nucleation-limited regime for very low tip bias. Using "interrupted-switching" m…
Recently, a method of ultrafast polarization switching in ferroelectrics has been suggested. The basic idea of the method is to employ the effect of self-acceleration of polarization dynamics due to a resonator feedback field. This is the idea of principle whose efficiency is demonstrated by an Ising-type model in a transverse field. Of course, the practical realization of the method requires the choice of appropriate materials, which is a separate problem. For example, the standard order-disorder ferroelectrics with spatially symmetric double-well potentials cannot be used for this purpose, s…
The critical current density $J_{c0}$ required for switching the magnetization of the free layer (FL) in a spin-transfer torque magnetic random access memory (STT-MRAM) cell is proportional to the product of the damping parameter, saturation magnetization and thickness of the free layer, $αM_S t_F$. Conventional FLs have the structure CoFeB/nonmagnetic spacer/CoFeB. By reducing the spacer thickness, W in our case, and also splitting the single W layer into two layers of sub-monolayer thickness, we have reduced $t_F$ while minimizing $α$ and maximizing $M_S$, ultimately leading to lower $J_{c0}…
Although several multiferroic materials/heterostructures have been extensively studied, finding strong magnetoelectric couplings for the electric field control of the magnetization remains challenging. Here, a novel interfacial magnetoelectric coupling based on three components (ferroelectric dipole, magnetic moment, and antiferromagnetic order) is analytically formulated. As an extension of carrier-mediated magnetoelectricity, the new coupling is shown to induce an electric-magnetic hysteresis loop. Realizations employing BiFeO$_3$ bilayers grown along the [$111$] axis are proposed. Without i…
Negative capacitance field-effect transistors (NC-FETs) have attracted wide interest as promising candidates for steep-slope devices, and sub-60 mV/decade switching has been demonstrated in NC-FETs with various device structures and material systems. However, the detailed mechanisms of the observed steep-slope switching in some of these experiments are under intense debate. Here we show that sub-60 mV/decade switching can be observed in a WS2 transistor with a metal-insulator-metal-insulator-semiconductor (MIMIS) structure - without any ferroelectric component. This structure resembles an NC-F…
Controlling magnetism using voltage is highly desired for applications, but remains challenging due to fundamental contradiction between polarity and magnetism. Here we propose a mechanism to manipulate magnetic domain walls in ferrimagnetic or ferromagnetic multiferroics using electric field. Different from those studies based on static domain-level couplings, here the magnetoelectric coupling relies on the collaborative spin dynamics around domain walls. Accompanying the reversal of spin chirality driven by polarization switching, a "rolling-downhill"-like motion of domain wall is achieved a…
Ferroelectric switching of interfacial dipoles in $α$-RuCl$_3$/graphene heterostructure
研究通过石墨烯/超薄hBN/α-RuCl₃异质结构实现了电可切换的铁电偶极子，揭示了界面电荷转移驱动的非易失偶极子开关机制。
Pulse-based studies of ferroelectric capacitor systems have been used by several groups to experimentally probe the mechanisms of apparent negative capacitance. In this paper, the behavior of such systems is modeled through SPICE simulation with a delayed-response Preisach model, and the results are compared to available data. It is found that a simple ferroelectric domain delay model can explain much of the observed behavior, capturing the qualitatively different effects of bipolar and unipolar switching, as well as the voltage dependence of said switching. The observed behavior and its model…
A microscopic view of the response of the electric dipoles to a dynamic external field in a ferroelectric (FE) chain has been studied by two spin dynamics methods. One is the prominent micromagnetic approach, and the other is the micromagnetic approach with a variable size of the pseudo-spin. The energy stored in the ferroelectric chain is described by the transverse Ising model (TIM) with electric pseudo-spins. The simulations are based on a modified Landau-Lifshitz-Gilbert (LLG) equation which is precession free. The results obtained are shown and compared with the result supplemented by Lan…
When Screening Current Controls Ferroelectric Switching: From Field-Limited to Current-Limited Regimes
本文通过实验和模拟揭示，在扫描探针下铁电翻转受屏蔽电流供应和再分布速率限制，提出屏蔽电流限制机制，并解释纳米尺度压电滞回测量中畴壁定律的失效，将电流调控作为确定性纳米畴工程的手段。
Water Induced Ferroelectric Switching: The Crucial Role of Collective Dynamics
本研究结合实验与大规模分子动力学模拟，揭示双层石墨烯纳米带通过边缘稳定锚定水团簇产生铁电效应，并展现出可用于铁电异质结构和神经形态电路的显著持久剩余场。
Selective and Quasi-continuous Switching of Ferroelectric Chern Insulator Device for Neuromorphic Computing
本研究通过双层对齐h-BN封装魔角扭曲双层石墨烯制备出铁电Chern绝缘体器件，利用精细控制的脉冲实现了1280个非易失性电阻态的选择性与准连续切换，并展示了其在抗噪声神经形态计算中的应用潜力。
Nanosecond Ferroelectric Switching of Intralayer Excitons in Bilayer 3R-MoS2 through Coulomb Engineering
本研究通过库仑工程调控双层3R-MoS2的激子峰分裂，实现了纳秒级铁电切换，折射率调制达4，反射率变化超85%，为高速非易失光学存储和可重构光子器件提供新方向。
Electrical switching of a moiré ferroelectric superconductor
本文在对齐BN的MATBG中发现与超导和关联绝缘态共存的铁电性，并通过栅压或位移场实现超导、金属及关联绝缘态间的可重复双稳态电切换。
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