在Born-Oppemheimer近似下，我们将自旋轨道耦合系统中的总电子哈密顿量分解为慢轨道运动和快带间跃迁过程。我们发现，快速运动诱导规范场慢轨道运动，垂直于电子动量，诱导拓扑相。从这个一般设计原理出发，我们提出了一种在抛物线渐变GaAs/In $_{x}$ Ga $_{1-x}$ As/GaAs量子阱中产生人工规范场和拓扑相的理论。通过调整反点晶格的刻蚀深度和周期，叠加势引起的能带折叠导致了能带的形成和相邻子带之间的能带反转。子带间的自旋轨道相互作用打开了相当大的非平凡的迷你间隙，并导致许多对螺旋边缘状态在这些间隙。
英文摘要：
Based on the Born-Oppemheimer approximation, we divide total electron Hamiltonian in a spinorbit coupled system into slow orbital motion and fast interband transition process. We find that the fast motion induces a gauge field on slow orbital motion, perpendicular to electron momentum, inducing a topological phase. From this general designing principle, we present a theory for generating artificial gauge field and topological phase in a conventional two-dimensional electron gas embedded in parabolically graded GaAs/In$_{x}$Ga$_{1-x}$As/GaAs quantum wells with antidot lattices. By tuning the etching depth and period of antidot lattices, the band folding caused by superimposed potential leads to formation of minibands and band inversions between the neighboring subbands. The intersubband spin-orbit interaction opens considerably large nontrivial minigaps and leads to many pairs of helical edge states in these gaps.
Geometrically frustrated materials, such as spin ice or kagome lattice, are known to exhibit exotic Hall effect phenomena due to spin chirality. We explore Hall effect mechanism in an artificial honeycomb spin ice of Nd--Sn element using Hall probe and polarized neutron reflectivity measurements. In an interesting observation, a strong enhancement in Hall signal at relatively higher temperature of $T$ $\sim$ 20 K is detected. The effect is attributed to the planar Hall effect due to magnetic moment configuration in spin ice state in low field application. In the antiferromagnetic state of neod…
Magnetic nanoarray with special geometries exhibits nontrivial collective behaviors similar to those observed in the spin ice materials. Here we present a novel circuit model to describe the complex magnetotransport phenomena in artificial kagome spin ice. In this picture, the system can be viewed as a resistor network driven by voltage sources that are located at vertices of the honeycomb array. The differential voltages across different terminals of these sources are related to the ice-rules that govern the local magnetization ordering. The circuit model relates the transverse Hall voltage o…
Vortex magnetic structure in artificial honeycomb lattice provides a unique platform to explore emergent properties due to the additional Berry phase curvature imparted by chiral magnetization to circulating electrons via direct interaction. We argue that while the perpendicularly-aligned magnetic component leads to the quantized flux of monopole at the center of the Berry sphere, the in-plane vortex circulation of magnetization gives rise to unexpected non-trivial topological Berry phase due to the gauge field transformation. The unprecedented effect signifies the importance of vector potenti…
The ability to engineer the electronic band structure and, more strikingly, to access new exotic phase of matter has been the cornerstone of the advance of science and technology. Twisting van der Waals materials to form moiré superlattice is a powerful paradigm and can drive graphene from a normal metallic state into an insulating, superconducting, or ferromagnetic states. Here, we present a new route to create non-trivial band structure and consequently an exotic phase of matter via lithographically patterned strain (lattice deformation). This method is used to realize an artificially corrug…
The even-denominator states have attracted considerable attention owing to their possible applications in future quantum technologies. In this letter, we first report a 3/2 diagonal resistance, indicating the existence of a 3/2 state in a nanometer-sized triple-gated quantum point contact (QPC) fabricated on a high-mobility (not ultra-high-mobility) single-layer two-dimensional (2D) GaAs wafer. The center gate plays a crucial role in realizing the QPC's 3/2 state. Our observation of the 3/2 state using a conventional QPC device, which is a suitable building block for semiconductor quantum devi…
Observation of the magnetic spin Hall effect in a ferromagnet
CIC nanoGUNE BRTA（纳米技术研究中心 nanoGUNE）；University of the Basque Country (UPV/EHU)（巴斯克大学）；Univ. Grenoble Alpes, CEA, CNRS, Grenoble-INP, SPINTEC（格勒诺布尔阿尔卑斯大学、法国原子能和替代能源委员会、法国国家科学研究中心、格勒诺布尔国立理工学院、自旋技术中心）；IKERBASQUE, Basque Foundation for Science（伊克尔巴斯克，巴斯克科学基金会）
The spontaneous Hall effect is usually governed by three conventional mechanisms, such as the Berry curvature, skew scattering and side jump, which widely exist in ferromagnetic or antiferromagnetic materials. However, in this work, based on first principle calculations, we predict a giant crystal Hall effect (CHE) in the antiferromagnetic $γ$-FeMn, which can not be understood by the previous three conventional mechanisms and the Hall angle therein can be as large as 18.4% at low temperature. Furthermore, with Boltzmann transport equation and a tight-binding model, we conclude that, the asymme…
Skyrmions with the topological number $Q$ equal an integer larger than 1 are called high-topological-number skyrmions or high-$Q$ skyrmions. In this work, we theoretically study the topological Hall effect in square-lattice high-$Q$ skyrmion crystals (SkX) with $Q=2$ and $Q=3$. As a result of the emergent magnetic field, Landau-level-like electronic band structure gives rise to quantized Hall conductivity when the Fermi energy is within the gaps between adjacent single band or multiple bands intertwined. We found that different from conventional ($Q=1$) SkX the Hall quantization number increas…
We extend the semiclassical Boltzmann formalism for the anomalous Hall effect (AHE) in nondegenerate multiband electron systems to the spin Hall effect (SHE) and unconventional Edelstein effect (UEE, cannot be accounted for by the conventional Boltzmann equation, unlike the conventional Edelstein effect). This extension is confirmed by extending the Kohn-Luttinger density-matrix transport theory in the weak disorder-potential regime. By performing Kubo linear response calculations in a prototypical multiband model, the Boltzmann scaling for the AHE/SHE and UEE is found to be valid only if the …
Spin Hall nano-oscillators (SHNOs) are promising candidates for new microwave oscillators with high durability due to a small driving current. However, conventional SHNOs with an in-plane precession (IPP) mode require a bias field for stable oscillations which is not favored in certain applications such as neuromorphic computing. Here, we propose and theoretically analyze a bias-field-free SHNO with an in-plane hard axis and an out-of-plane precession (OPP) mode by solving the Landau-Lifshitz-Gilbert (LLG) equation analytically and numerically. We derive formulas for driving currents and prece…
Hilbert-space selected switch of helical edges in an artificial quantum Hall insulator
Shanxi University（山西大学）；Liaoning Academy of Materials（辽宁省材料研究院）；ShanghaiTech University（上海科技大学）；National Institute for Materials Science（国立材料研究所）；Southeast University（东南大学）；Fudan University（复旦大学）
Density-controlled quantum Hall ferromagnetic transition in a two-dimensional hole system
量子霍尔铁磁跃迁通常通过原位样品旋转增加塞曼能量来实现，而具有伪自旋指数的系统中的跃迁可以通过栅极控制来诱导。本文报道了在没有面内磁场的二维系统中两个实自旋态之间的门控量子霍尔铁磁跃迁。我们发现，在Ge二维空穴系统中，由于载流子间的相互作用，塞曼分裂与回旋能隙的比值随密度的减小而增大。在$\sim2.4\times 10^{10}$ cm $^{-2}$的临界密度以下，该比率增长大于$1$，导致填充因子为$ν=2$的铁磁基态。在临界密度下，观察到由于形成相反自旋取向的微观畴而导致的电阻峰。这种门控自旋极化在量子霍尔制度打开了大门，实现马约拉纳模式使用二维系统在传统的，低自旋轨道耦合半导体。
Realization of the quantum-spin-Hall effect in graphene devices has remained an outstanding challenge dating back to the inception of the field of topological insulators. Graphene's exceptionally weak spin-orbit coupling -stemming from carbon's low mass- poses the primary obstacle. We experimentally and theoretically study artificially enhanced spin-orbit coupling in graphene via random decoration with dilute Bi2Te3 nanoparticles. Remarkably, multi-terminal resistance measurements suggest the presence of helical edge states characteristic of a quantum-spin-Hall phase; the magnetic-field and te…
We report on transport signatures of hidden quantum Hall stripe (hQHS) phases in high ($N > 2$) half-filled Landau levels of Al$_{x}$Ga$_{1-x}$As/Al$_{0.24}$Ga$_{0.76}$As quantum wells with varying Al mole fraction $x < 10^{-3}$. Residing between the conventional stripe phases (lower $N$) and the isotropic liquid phases (higher $N$), where resistivity decreases as $1/N$, these hQHS phases exhibit isotropic and $N$-independent resistivity. Using the experimental phase diagram we establish that the stripe phases are more robust than theoretically predicted, calling for improved theoretical treat…
Artificial Neural Network (ANN) -- Oscillatory Neural Network (ONN) Hybrid System Using Domain-Wall Synapse Devices and Nano-Constriction Spin Hall Nano Oscillators
Indian Institute of Technology Bombay（印度理工学院孟买分校）；Centre for Semiconductor Technologies (SemiX), Indian Institute of Technology Bombay（印度理工学院半导体技术中心 (SemiX)）
Any departure from graphene's flatness leads to the emergence of artificial gauge fields that act on the motion of the Dirac fermions through an associated pseudomagnetic field. Here, we demonstrate the tunability of strong gauge fields in non-local experiments using a large planar graphene sheet that conforms to the deformation of a piezoelectric layer by a surface acoustic wave. The acoustic wave induces a longitudinal and a giant synthetic Hall voltage in the absence of external magnetic fields. The superposition of a synthetic Hall potential and a conventional Hall voltage can annihilate t…
The exsitance of three-dimensional Hall effect (3DQHE) due to spontaneous Fermi surface instabilities in strong magnetic field was proposed decades ago, and has stimulated recent progress in experiments. The reports in recent experiments show that the Hall plateaus and vanishing transverse magneto-resistivities (TMRs) (which are two main signatures of 3DQHE) are not easy to be observed in natural materials. And two main different explanations of the slow varying slope like Hall plateaus and non-vanishing TMRs (which can be called as quasi-quantized Hall effect (QQHE)) have been proposed. By st…
Giant Nernst and Hall Effects in Chiral Superconductors due to Berry Phase Fluctuations
我们考虑了在相变温度以上的手征超导体涨落区中的能斯特效应和霍尔效应，它们不是由传统的洛伦兹力引起的，而是由Bogoliubov-de Gennes哈密顿量的Berry相涨落引起的非对称散射引起的.结果发现，这些效果可以比传统的清洁样品，表现出定性不同的行为更显着。这些结果为最近在干净的URu $_2$ Si $_2$样品中观察到的能斯特效应提供了系统和全面的理解，该样品被认为是一种手征超导体。
Observations of electron-hole asymmetry in transport through graphene devices at high magnetic field challenge prevalent models of the graphene quantum Hall effect. Here, we study this asymmetry both in conventional magnetotransport and in scanning gate microscopy maps measured in an encapsulated graphene constriction. We reveal that the presence of upstream modes and local doping in the vicinity of electrical contacts leads to a totally different picture of topological breakdown for electrons and holes, explaining the observed asymmetry.
We develop a hydrodynamic theory for an electron system exhibiting the anomalous Hall effect, and show that an additional anomalous Hall effect is induced by a vorticity generated near boundaries. We calculate the momentum flux and force proportional to the electric field using linear response theory. The hydrodynamic equation is obtained by replacing the local electric field with the electric current, focusing on a scale that is sufficiently larger than the mean free path. It is demonstrated that there is a coupling between a vorticity of an electric current and a magnetization which generate…
