Pseudospin and Deformation-induced Gauge Field in Graphene
K. Sasaki, R. Saito
从赝自旋和与赝自旋耦合的规范场的角度，综述了石墨烯中费米能级附近$π$电子的基本性质。本文报道了规范场在电子-声子相互作用和边缘态中的应用。
The basic properties of $π$-electrons near the Fermi level in graphene are reviewed from a point of view of the pseudospin and a gauge field coupling to the pseudospin. The applications of the gauge field to the electron-phonon interaction and to the edge states are reported.
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The energy spectrum of planar polytype graphene-based superlattices has been investigated. It is shown that their energy spectrum undergoes pseudospin splitting due to the asymmetry of quantum wells forming the superlattice potential profile.
Pseudospin in optical and transport properties of graphene
我们表明，赝自旋是一个额外的自由度的载体在石墨烯中可以有效地控制通过电子-电子相互作用，这反过来又可以通过改变基板来操纵。特别是，一个平面外的赝自旋组件可以发生导致零场霍尔电流以及偏振敏感的带间光吸收。
Gate-dependent Pseudospin Mixing in Graphene/Boron Nitride Moire Superlattices
石墨烯中的电子由具有双组分赝自旋的相对论性Dirac-Weyl旋量描述1 -12。狄拉克电子独特的赝自旋结构导致了新出现的现象，如无质量的狄拉克锥2，反常量子霍尔效应2，3和克莱因隧道4，5在石墨烯。操纵电子赝自旋的能力对于新型石墨烯电子学是高度期望的，并且它需要精确控制以在原子水平上区分两个石墨烯子晶格。石墨烯/氮化硼（石墨烯/BN）莫尔超晶格，其中由于B-N原子导致的快速子晶格振荡叠加在缓慢莫尔周期上，提供了一种有吸引力的方法来设计石墨烯中的电子赝自旋13 -18。这种不寻常的莫尔超晶格导致旋量势与不寻常的电子赝自旋杂交，这可以直接通过红外光谱探测，因为光学跃迁对激发态波函数非常敏感。在这里，我们进行石墨烯/BN异质结构的显微红外光谱，并证明莫尔超晶格势是由一个pseudospin-mixing组件类似于一个空间变化的伪磁场占主导地位。此外，我们表明，旋量势敏感地依赖于栅极诱导的载流子浓度在石墨烯，表明从电子-电子相互作用的旋量势的强重整化。我们的研究提供了更深入的理解下旋量莫尔势的石墨烯赝自旋结构，以及令人兴奋的机会，以控制赝自旋在二维异质结构的新型电子和光子纳米器件。
Pseudospin valve in bilayer graphene: towards graphene-based pseudospintronics
我们提出了一个非磁性的，基于赝自旋的自旋阀的版本，其中在相邻区域的石墨烯双层的赝自旋极化由外部门控制。数值计算表明这种器件具有较大的开关比。这一发现为赝自旋电子学的实现提供了希望：一种基于赝自旋操纵的电子学形式，类似于自旋电子学应用中对物理自旋的控制。
The possibility of transporting spin information over long distances in graphene, owing to its small intrinsic spin-orbit coupling (SOC) and the absence of hyperfine interaction, has led to intense research into spintronic applications. However, measured spin relaxation times are orders of magnitude smaller than initially predicted, while the main physical process for spin dephasing and its charge-density and disorder dependences remain unconvincingly described by conventional mechanisms. Here, we unravel a spin relaxation mechanism for nonmagnetic samples that follows from an entanglement bet…
Pseudospin for Raman D Band in Armchair Graphene Nanoribbons
通过解析构造扶手椅型石墨烯纳米带拉曼光谱中$D$带的电子-声子相互作用的矩阵元，我们表明赝自旋和动量守恒导致（i）由两个分量组成的$D$带，（ii）仅当入射光和散射光的偏振平行于扶手椅边缘时，$D$带拉曼强度增强，以及（iii）由Kohn异常效应引起的$D$带软化/硬化行为与$G$带的软化/硬化行为相关。几个实验中提到的是相关的这些结果。赝自旋与声子模的边界条件无关，而动量守恒依赖于边界条件。
Berry Phase and Pseudospin Winding Number in Bilayer Graphene
自从双层石墨烯中发现了新颖的量子霍尔效应，并用2 π [K]的Berry相来解释以来，S. Novoselov等人，“Unconventional量子霍尔效应and Berry's phase of 2pi in bilayer graphene”，Nature Phys.2，177（2006）]，已经广泛接受的是，该系统中的低能电子波函数由不同于常规二维电子气的零相的2pi的非平凡Berry相描述。在这里，我们表明：（i）双层石墨烯的相关Berry相位与传统的二维电子气没有什么不同（正如预期的那样，假设Berry相位仅对2pi有意义），以及（ii）在量子霍尔测量中实际观察到的不是Berry相位的绝对值，而是赝自旋缠绕数。
Electronic states in 2D materials can exhibit pseudospin degrees of freedom, which allow for unique carrier-field interaction scenarios. Here, we investigate ultrafast sublattice pseudospin relaxation in graphene by means of polarization-resolved photoluminescence spectroscopy. Comparison with microscopic Boltzmann simulations allows to determine a lifetime of the optically aligned pseudospin distribution of $12\pm 2\,\text{fs}$. This experimental approach extends the toolbox of graphene pseudospintronics, providing novel means to investigate pseudospin dynamics in active devices or under exte…
The Dirac electrons of graphene, an intrinsic zero gap semiconductor, uniquely carry spin and pseudospin that give rise to many fascinating electronic and transport properties. While isolated zigzag graphene nanoribbons are antiferromagnetic semiconductors, we show by means of first-principles and tight-binding calculations that zigzag graphene nanoribbons supported on graphene are half-metallic as a result of spin- and pseudospin-symmetry breaking. In particular, half-metallic Dirac cones are formed at K (K') near the Fermi level. The present results demonstrate that the unique combination of…
Nonequilibrium effective vector potential due to pseudospin exchange in graphene
我们表明，交换相互作用的二维电子气体平衡可以产生一个虚构的矢量势与有趣的签名在干涉和霍尔测量。详细的预测石墨烯，其中的效果是增强的赝自旋交换。
Vortex is a universal and significant phenomenon that has been known for centuries. However, creating vortices to the atomic limit has remained elusive because that the characteristic length to support a vortex is usually much larger than the atomic scale. Very recently, it was demonstrated that intervalley scattering induced by the single carbon defect of graphene leads to phase winding over a closed path surrounding the defect. Motivated by this, we demonstrate, in this Letter, that the single carbon defects at A and B sublattices of graphene can be regarded as pseudospin-mediated atomic-sca…
Spontaneous Layer-Pseudospin Domain Walls in Bilayer Graphene
双层石墨烯易受具有自旋和谷依赖层极化的不寻常的对称性破缺状态的影响。我们报告在这些系统中的畴壁的微观研究，表明他们有有趣的微观结构有关的秩序诱导的拓扑字符。我们使用我们的结果来估计Ginzburg-Landau模型参数和双层石墨烯有序态的转变温度。
Modifying the hexagonal lattices of graphene enables the repositioning and merging of the Dirac cones which proves to be a key element in the use of these materials for alternative electronic applications such as valleytronics. Here we study the nonequilibrium transport of carriers within a system containing two Dirac cones in both standard graphene and semi-Dirac graphene. In the latter, the lattice modifications cause the relativistic and parabolic dispersion bands to coexist, furnishing the Fermi surface with a rich pseudospin texture and a versatile Dirac cones separation. We construct a k…
Hamiltonian and eigenstate problem is formulated for a bilayer graphene in terms of Clifford's geometric algebra \textit{Cl}$_{3,1}$. It is shown that such approach allows to perform analytical calculations in a simple way if geometrical algebra rotors are used. The measured quantities are express through spectrum and rotation half-angle of the pseudospin that appears in geometric algebra rotors. Properties of free charge carriers -- pseudospin, velocity and Berry phase -- in a bilayer graphene are investigated in the presence of the external voltage applied between the two layers.
Quantum transport of pseudospin-polarized Dirac fermions in gapped graphene nanostructures
我们研究了带隙单层石墨烯中的量子输运特性，该石墨烯处于赝自旋破缺态，具有净垂直赝磁化。利用这些赝铁磁体，我们提出了一个完美的赝自旋阀效应，可用于实现赝自旋电子学在单层石墨烯。研究了赝自旋注入和赝自旋积累联合效应的特点。我们进一步证明了亚晶格赝自旋自由度对Andreev反射的决定性影响以及PF和超导体在S/PF和PF/S/PF几何结构中的混合结构中的邻近效应。特别是，我们发现了一个奇特的Andreev反射，这是与反转的z分量的载流子赝自旋矢量。我们的研究结果表明，带隙的正常石墨烯的行为像一个铁磁石墨烯和赝自旋自由度的影响，在带隙的石墨烯是一样重要的自旋在铁磁石墨烯。
Pseudospin, an additional degree of freedom inherent in graphene, plays a key role in understanding many fundamental phenomena such as the anomalous quantum Hall effect, electron chirality and Klein paradox. Unlike the electron spin, the pseudospin was traditionally considered as an unmeasurable quantity, immune to Stern-Gerlach-type experiments. Recently, however, it has been suggested that graphene pseudospin is a real angular momentum that might manifest itself as an observable quantity, but so far direct tests of such a momentum remained unfruitful. Here, by selective excitation of two sub…
Pseudospin polarized quantum transport in monolayer graphene
单层石墨烯的能隙提出了一个赝自旋对称性破缺铁磁体与垂直的赝磁化，其方向是通过改变n和p之间的掺杂类型切换。我们证明了电流开关效应在赝自旋版本的自旋阀，其中两个赝铁磁区域通过正常的石墨烯区域接触。所提出的结构具有伪磁阻，定义为伪磁化的平行和反平行排列的电阻的相对差，其可以被调谐到统一。这种完美的伪磁开关被发现表现出很强的鲁棒性，相对于增加的接触长度，我们解释的效果在一个不寻常的长范围渗透到正常区域的平衡赝自旋极化接近赝铁磁体。我们的研究结果揭示了带隙石墨烯实现基于赝自旋的纳米电子学的潜力。
Chiral quasiparticles in Bernal-stacked bilayer graphene have valley-contrasting Berry phases of 2π. This nontrival topological structure, associated with the pseudospin winding along a closed Fermi surface, is responsible for various novel electronic properties, such as anti-Klein tunneling, unconventional quantum Hall effect, and valley Hall effect1-6. Here we show that the quantum interference due to intervalley scattering induced by atomic defects/impurities provides further insights into the topological nature of the bilayer graphene. The scattered chiral quasiparticles between distinct v…
Strong spin-orbit interaction (SOI) in graphene grown on tungsten disulfide (WS2) has been recently observed, leading to energy gap opening by SOI. Energy gap in graphene may also be induced by sublattice symmetry breaking (SSB) where energy level in A-sublattice is not equal to that in B-sublattice. SSB-gap may be produced by growing graphene on hexagonal boron nitride or silicon carbide. In this work, we investigate transport property in a SOI/SSB/SOI gapped graphene junction, focusing the effect of interplay of SOI and SSB. We find that, lattice-pseudospin polarization (L-PSP) can be contro…
We have investigated the role of pseudospin polarization in electron wave packet dynamics in pristine graphene and in a graphene antidot lattice subject to an external magnetic field. Employing a Green's function formalism, we show that the electron dynamics can be controlled by tuning pseudospin polarization. We find that in Landau quantized pristine graphene both the propagation of an electron wave packet and Zitterbewegung oscillations strongly depend on pseudospin polarization. The electron wave packet is found to propagate in the direction of initial pseudospin polarization. We also show …
Note on lattice spin in graphene and "spin from isospin" phenomenon
众所周知，在紧束缚近似下，石墨烯蜂窝晶格中K/K'点附近的低能电子动力学可以用2+1无质量Dirac方程描述。石墨烯的自旋等价物，“赝自旋”，是由蜂窝晶格的每个单元格的两个不等价原子位置引入的简并引起的。Mecklenburg和Regan（Phys. Rev. Lett. 106（2011），116803）已经表明，与通常的观点相反，赝自旋具有实角动量的所有属性。在某些情况下，内部对称性可以对角动量产生重要的贡献。这种现象在粒子物理学中已经知道很多年了，并被称为“来自同位旋的自旋”。我们表明，类似的机制工作的情况下，晶格赝自旋。
Optimal spin-charge interconversion in graphene through spin-pseudospin entanglement control
本文提出通过控制自旋-赝自旋纠缠，在石墨烯中利用Rashba-Edelstein效应实现100%效率的自旋-电荷互转换，并发现无序鲁棒的自旋霍尔效应，为自旋电子器件提供新机制。
Pseudospin rotation and valley mixing in electron scattering at graphene edges
在石墨烯中，赝自旋和谷味作为新类型的量子自由度出现，这是由于蜂窝晶格分别包括布里渊区中的两个子晶格（A和B）和两个不等价的狄拉克点（K和K '）。石墨烯独特的电子性质导致了诸如克莱因隧道效应、维斯拉格透镜和谷极化电流等引人注目的现象。在这里，我们调查的赝自旋和谷在石墨烯边缘的电子散射的作用，并表明它们是强烈相关的短波长振荡和缓慢衰减的拍模式的电荷密度调制。用最近邻紧束缚方法和第一性原理密度泛函理论计算的理论分析与我们的扫描隧道显微镜的实验数据吻合得很好。我们相信，这项研究将导致有用的应用石墨烯的“谷电子学”和“赝自旋电子学”。
Pseudospin entanglement and Bell test in graphene
我们提出了一种在石墨烯中产生和检测电子和空穴之间的赝自旋纠缠的方法。电子-空穴对由涨落势产生，它们的纠缠由电流相关测量证明。石墨烯中的电子的手性促进了具有在真实空间中定义的（伪）自旋投影角的良好控制的贝尔测试。
Ultimate In-plane Magnetoresistance Ratio of Graphene by Controlling the Gapped Dirac Cone through Pseudospin
本文通过赝自旋控制Ni(111)夹持石墨烯的狄拉克锥带隙，实现高达1450%的磁阻，并预测纳米尺度宽度可达到极限磁阻。
Role of pseudospin in quasiparticle interferences in epitaxial graphene probed by high-resolution scanning tunneling microscopy
赝自旋是与石墨烯蜂窝结构相关的额外自由度，是这种材料中发现的许多突出电子特性的原因。这篇文章提供了一个清晰的理解，这样的赝自旋影响的准粒子干扰的单层（ML）和双层（BL）石墨烯测量低温扫描隧道显微镜和光谱。我们已经使用这种技术来映射，具有非常高的能量和空间分辨率，在本机无序的存在下，在SiC（0001）上外延生长的ML和BL石墨烯的局域态密度的空间调制。我们执行这样的调制，包括波矢量的倒易晶格的单位矢量的傅立叶变换分析。我们的数据表明，准粒子的干扰与一些特定的散射过程被抑制在ML石墨烯，但不是在BL石墨烯。最重要的是，与谷内背散射相关的2qF波矢量的干扰在ML石墨烯中没有测量到，即使在具有最高分辨率的图像上也是如此。为了阐明赝自旋在准粒子干涉中的作用，我们使用了一个简单的模型，它很好地捕捉了我们数据上观察到的主要特征。该模型明确地表明，石墨烯的赝自旋是负责这种抑制ML石墨烯中的准粒子干扰功能，特别是那些与2qF波矢。这也证实了扫描隧道显微镜是一种独特的技术，可以在纳米精度的真实空间中探测石墨烯样品中的赝自旋。最后，我们表明，这样的观察是强大的能量和获得高精度的分散的π带ML和BL石墨烯在费米能级附近，提取其主要的紧束缚参数。
Pseudo-zero-mode Landau levels and pseudospin waves in bilayer graphene
在磁场中的双层石墨烯支持八个零能量朗道能级，随着可调带隙的发展，这些朗道能级演变成由带隙分开的两个近简并的四重态。一个密切关注的性质，这样一个孤立的四重态的伪零模能级在半填充的存在下，在一个平面内的电场和库仑相互作用。伪零模水平原来支持，通过轨道混合，电荷载流子与诱导的电偶极矩，这导致特征集体激发，pseudosin波，具有一些可控的功能，可能的实验信号进行了讨论。
Intense Terahertz Laser Fields Induced and Manipulated Pseudospin Polarization in Graphene
利用Floquet定理，通过精确求解含时薛定谔方程，研究了单层石墨烯在强太赫兹激光场作用下赝自旋依赖的密度-能量关系.我们发现圆偏振太赫兹激光场可以诱导赝自旋极化。当K谷和K $^{\prime}$谷的电子密度相等时，这两个谷的赝自旋极化可以正好相反.此外，我们还发现赝自旋极化可以通过场的强度、频率，特别是极化方向来控制。
Magnetoelectric coupling, Berry phase, and Landau level dispersion in a biased bilayer graphene
研究了横向电场和磁场作用下石墨烯双层膜的能谱。我们发现，由此产生的朗道能级表现出非单调依赖的电场，以及许多水平交叉。这种行为是解释使用准经典量子化规则，适当地考虑到赝自旋的准粒子。赝自旋产生Berry相，这导致能量量子化的移动，并导致赝塞曼效应。后者依赖于电场，在两个谷之间符号交替，并且还减小带隙。其他赝自旋相关的量，如异常霍尔电导率的解析公式，推导和以前的理论工作相比。
Size Quantization in Planar Graphene-Based Heterostructures: Pseudospin Splitting, Interface States, and Excitons
研究了由边缘与带隙石墨烯片接触的无隙石墨烯纳米颗粒制成的平面量子阱器件。非对称量子阱中载流子的尺寸量子化谱显示出赝自旋分裂。一种新型的界面态产生于无隙和有隙石墨烯材料的色散曲线的交叉。计算了平面石墨烯量子阱的激子谱。分析了外加电场对激子谱的影响。
Momentum-space Observation of Optically Excited Non-Thermal Electrons in Graphene with Persistent Pseudospin Polarization
本文利用时间分辨动量显微技术观测石墨烯中光激发非热电子的动量分布与赝自旋极化，并通过调节激发通量揭示电子-电子散射对极化弛豫的影响，为二维材料研究和石墨烯器件设计提供依据。
Magnetoresistance in Disordered Graphene: The Role of Pseudospin and Dimensionality Effects Unraveled
我们报告了一个理论低场磁输运研究揭示了赝自旋在弱无序石墨烯基材料的现实模型的影响。使用一个有效的久保计算方法，并模拟氧化物中捕获的电荷的影响，不同的磁导指纹的数值获得的系统尺寸大至0.3平方微米，含有数千万个碳原子。在二维石墨烯中，发现强谷混合不可挽回地产生正的磁导（弱局部化），而从正到负的磁导（弱反局部化）的交叉是通过将无序强度降低到弹道极限来获得的。与此形成鲜明对比的是，横向尺寸为10 nm的石墨烯纳米带没有表现出弱反局域化的迹象，即使是非常小的无序强度。我们的研究结果合理的出现一个复杂的相图的磁导指纹，脱落的微观起源的赝自旋效应的一些新的光。
We foretell a new pseudospin-dependent phenomenon in mono-layer graphene (MLG), which is numerically simulated \emph{via} an innovator nano-spintronic device. We proposed a novel theoretical procedure for describing the dynamics of Dirac fermions, departing from classic theoretical modelling. More importantly, we have found appealing evidences of wiggling anti-phase oscillations in the probability density time-distribution for each sub-lattice state, which we called pseudospinorial Zitterbewegung effect (PZBE). The PZBE undergoes modulated by a robust transient character, with decay time of fe…
Interband optical transitions in graphene are subject to pseudospin selection rules. Impulsive excitation with linearly polarized light generates an anisotropic photocarrier occupation in momentum space that evolves at timescales shorter than 100fs. Here, we investigate the evolution of non-equilibrium charges towards an isotropic distribution by means of fluence-dependent ultrafast spectroscopy and develop an analytical model able to quantify the isotropization process. In contrast to conventional semiconductors, the isotropization is governed by optical phonon emission, rather than electron-…
Pseudospin Order in Monolayer, Bilayer, and Double-Layer Graphene
石墨烯是一种无带隙半导体，其中传导和价带波函数的不同仅在于它们在材料的二维蜂窝晶体结构的两个子晶格上的投影之间的相位差。我们解释了为什么这种情况下创建开口的对称性破缺状态，包括反铁磁状态在单层和双层石墨烯和激子凝聚体在双层石墨烯，这是动量空间类似物的实空间秩序中常见的强局部相互作用的系统。我们讨论了这三种对称性破缺状态之间的一些相似之处和一些差异。
Spin manipulation is one of the most critical challenges to realize spin-based logic devices and spintronic circuits. Graphene has been heralded as an ideal material to achieve spin manipulation but so far new paradigms and demonstrators are limited. Here we show that certain impurities such as fluorine ad-atoms, which locally break sublattice symmetry without the formation of strong magnetic moment, could result in a remarkable variability of spin transport characteristics. The impurity resonance level is found to be associated with a long range sublattice pseudospin polarization, which by lo…
Based on the quantum kinetic equations for systems with SU(2) structure, regularization-free density and pseudospin currents are calculated in graphene realized as the infinite mass-limit of electrons with quadratic dispersion and a proper spin-orbit coupling. Correspondingly the currents possess no quasiparticle part but only anomalous parts. The intraband and interband conductivities are discussed with respect to magnetic fields and magnetic domain puddles. It is found that the magnetic field and meanfield of domains can be represented by an effective Zeeman field. For large Zeeman fields th…
Quantum and classical confinement of resonant states in a trilayer graphene Fabry-Perot interferometer
少层石墨烯的出现产生了一个新的二维系统家族，该系统具有由相对论量子力学控制的新兴电子特性。多层碳亚晶格赋予了电子波函数赝自旋，相对论电子自旋的晶格模拟，而多层结构导致电场效应可调谐的电子带。在这里，我们使用这些属性来实现巨大的电导振荡弹道三层石墨烯法布里-珀罗干涉仪，这是由于通过静电势垒下的共振束缚态的相位相干传输。我们通过选择性地将这些状态与引线解耦来掩盖这些状态，从而通过非共振状态进行传输并抑制巨振荡。隐形可以通过两种方法来实现，一种是经典的，用磁场操纵准粒子动量，另一种是量子力学的，通过局部改变载波波函数的赝自旋特征。我们的研究结果说明了三层石墨烯作为电子光学和赝自旋电子学的通用平台的独特潜力。
Linear response of doped graphene sheets to vector potentials
二维无质量狄拉克费米子气体是描述单层石墨烯中低能电子的一个非常有用的模型。由于超导电流算符与（亚晶格）赝自旋算符成正比，描述对矢量势的响应的超导电流-电流响应函数恰好与赝自旋-赝自旋响应函数重合。在这项工作中，我们提出了分析结果的波矢量和频率依赖的纵向和横向的赝自旋赝自旋响应函数的非相互作用的MDF。在静态极限的横向响应，然后用来计算非相互作用的轨道磁化率。这些结果是一个出发点的近似赝自旋赝自旋响应函数的建设，将考虑电子-电子相互作用（例如在随机相位近似水平）。它们也构成了一个非常有用的输入电流密度泛函理论的石墨烯片受到时间和空间变化的矢量势的未来应用。
The pseudospin quantum degree of freedom is one of the most remarkable properties of graphene that distinguishes it from ordinary two-dimensional metals and semiconductors. Pseudospin quantum interference leads to weak antilocalization (WAL) and is influenced strongly by point defects and thermal perturbations that break chirality and destroy phase coherence. Preserving and manipulating quantum transport properties up to room temperature is key to realizing practical pseudospin-based graphene devices. Here we report fabrication and transport characterization of graphene field-effect devices on…
We present a detailed theoretical study of bilayer-graphene's electronic properties in the presence of electric and magnetic fields. Using group-theoretical methods, we derive an invariant expansion of the Hamiltonian for electron states near the K point of the Brillouin zone. In contrast to known materials, including single-layer graphene, any possible coupling of physical quantities to components of the external electric (magnetic) field has a counterpart where the analogous component of the magnetic (electric) field couples to exactly the same combination of quantities. For example, a purel…
The control of physical properties of solids with short laser pulses is an intriguing prospect of ultrafast materials science. Continuous-wave high-frequency laser driving with circular polarization was predicted to induce a light-matter coupled new state possessing a quasi-static band structure with an energy gap and a quantum Hall effect, coined "Floquet topological insulator". Whereas the envisioned Floquet topological insulator requires well separated Floquet bands and therefore high-frequency pumping, a natural follow-up question regards the creation of Floquet-like states in graphene wit…
Possible gapless helical edge states in hydrogenated graphene
本文通过第一性原理与紧束缚模型研究氢化石墨烯，发现改变氢化图案可实现约1 eV带隙及受对称性保护的拓扑螺旋边缘态，为赝自旋器件应用提供新途径。
Wavefront-Dislocation Evolution via Quadratic Band Touching Annihilation
研究通过二次能带接触湮灭揭示波前位错演化由赝自旋缠绕主导，而非拓扑电荷。
The pseudospin of Dirac electrons in graphene manifests itself in a peculiar momentum anisotropy for photo-excited electron-hole pairs. These interband excitations are in fact forbidden along the direction of the light polarization, and are maximum perpendicular to it. Here, we use time- and angle-resolved photoemission spectroscopy to investigate the resulting unconventional hot carrier dynamics, sampling carrier distributions as a function of energy and in-plane momentum. We first show that the rapidly-established quasi-thermal electron distribution initially exhibits an azimuth-dependent te…
The chiral two-dimensional electron gas in Landau levels $\left\vert N\right\vert >0$ of a Bernal-stacked graphene bilayer has a valley-pseudospin Ising quantum Hall ferromagnetic behavior at odd filling factors $ν_{N}=1,3$ of these fourfold degenerate states. At zero interlayer electrical bias, the ground state at these fillings is spin polarized and electrons occupy one valley or the other while a finite electrical bias produces a series of valley pseudospin-flip transitions. In this work, we extend the Ising behavior to chirally-stacked multilayer graphene and discuss the hysteretic behavio…
Creating Magnetic Fields in excess of 1000 T by Misoriented Stacking in a Graphene Bilayer
石墨烯单层中的晶格形变改变了电子在亚晶格中的跳跃，影响了电子的面内运动，可以产生高达100 T的面外赝磁场.在这里，我们证明了石墨烯双层中的堆叠取向差模拟了大于1000 T的巨大面内伪磁场对电子层间跳跃的影响。除了讨论面内赝磁场和扭曲对Bernal石墨烯双层电子能带结构的影响之间的相似性之外，我们还指出，面内磁场（或扭曲）可以改变石墨烯双层的低能赝自旋织构（赝自旋缠绕数从2减少到1），从而将准粒子的手征性从自旋1改变为自旋1/2。我们的研究结果说明了通过引入面内磁场或扭曲来可控地操纵Bernal石墨烯双层的电子性质的可能性。
Beating Fabry-Pérot interference pattern in a magnonic scattering junction in the graphene quantum Hall ferromagnet
研究石墨烯量子霍尔铁磁体中 $ν=-1|0|-1$ 磁子结的Fabry-Pérot干涉，发现极化基态下不同模式干涉产生拍频图样，为揭示低能各向异性提供依据。
We present a theory of superconductivity in twisted bilayer graphene in which attraction is generated between electrons on the same honeycomb sublattice when the system is close to a sublattice polarization instability. The resulting Cooper pairs are spin-polarized valley-singlets. Because the sublattice polarizability is mainly contributed by interband fluctuations, superconductivity occurs over a wide range of filling fraction. It is suppressed by i) applying a sublattice polarizing field (generated by an aligned BN substrate) or ii) changing moiré band filling to favor valley polarization. …
Friedel oscillation is a well-known wave phenomenon, which represents the oscillatory response of electron waves to imperfection. By utilizing the pseudospin-momentum locking in gapless graphene, two recent experiments demonstrate the measurement of the topological Berry phase by corresponding to the unique number of wavefront dislocations in Friedel oscillations. Here, we study the Friedel oscillations in gapped graphene, in which the pseudospin-momentum locking is broken. Unusually, the wavefront dislocations do occur as that in gapless graphene, which expects the immediate verification in t…
One of the intriguing characteristics of honeycomb lattices is the appearance of a pseudo-magnetic field as a result of mechanical deformation. In the case of graphene, the Landau quantization resulting from this pseudo-magnetic field has been measured using scanning tunneling microscopy. Here we show that a signature of the pseudo-magnetic field is a local sublattice symmetry breaking observable as a redistribution of the local density of states. This can be interpreted as a polarization of graphene's pseudospin due to a strain induced pseudo-magnetic field, in analogy to the alignment of a r…
Lattice Theory of Pseudospin Ferromagnetism in Bilayer Graphene: Competing Orders and Interaction Induced Quantum Hall States
在平均场理论中，双层石墨烯的大量狄拉克费米子模型具有一族破坏的反转对称性基态，其具有电荷间隙和风味依赖的自发层间电荷转移。我们使用晶格Hartree-Fock模型来探索一些物理控制是否这种类型的对称性破缺状态，它可以被视为一个赝自旋铁磁体，发生在自然界中。我们发现，反演对称性仍然是破缺的晶格模型和估计，转移面密度为$\sim 10^{-5}$电子每碳原子，相关的能隙是$\sim 10^{-2} {\rm eV}$，有序凝聚能是$\sim 10^{-7} eV$每碳原子，和竞争订单之间的能量差在中性点是$\sim 10^{-9} eV$每碳原子。我们探讨了由外部磁场和外部控制的层间电势差引起的量子相变。我们发现，特别是，在一个外部磁场耦合到自发的轨道时刻有利于打破时间反转对称状态，有自发量子化的异常霍尔效应。我们的理论预测的带隙在中性作为层间电势差的函数的非单调行为与最近的实验定性一致。
Chirality-Assisted Electronic Cloaking in Bilayer Graphene Nanostructures
我们发现双层石墨烯中赝自旋取向和载流子运动的强耦合对弹道p-n-p结的输运性质有着显著的影响。平行于势垒的零动量电子态被限制在它下面的一个赝自旋方向，而相反的赝自旋隧道通过结的状态完全不受限制状态的存在。我们证明，结作为一个斗篷的限制状态，使它们几乎不可见的电子在外部区域的入射角的范围内。这种行为表现在两端电导中，作为具有非洛伦兹奇异峰形状的传输共振。这些现象对弱磁场或电场诱导的层间间隙的响应可以作为电子隐身的实验指纹。
We develop a theory for the optical conductivity of doped multilayer graphene including the effects of electron-electron interactions. Applying the quantum kinetic formalism, we formulate a set of pseudospin Bloch equations that governs the dynamics of the nonequilibrium density matrix driven by an external \emph{a.c.} electric field under the influence of Coulomb interactions. These equations reveal a dynamical mechanism that couples the Drude and interband responses arising from the chirality of pseudospin textures in multilayer graphene systems. We demonstrate that this results in an intera…
Low-energy trions in graphene quantum dots
在包络函数近似下，我们研究了石墨烯量子点中三电子的低能态。在石墨烯中谷赝自旋作为除了自旋之外的电子自由度的存在增加了交换对称性和trion中的电子-电子相互作用之间的相互作用的卷积，导致trion的新状态以及不同于半导体中的低能量trion光谱。由于谷赝自旋的参与，低能谱几乎是简并的，由具有反对称性的态组成（pseudospin）（spin）分量在波函数中，自旋（赝自旋）部分是单线态（三线态）或三线态（单线态），这与半导体中的光谱相反，半导体的基态已知是非简并的，并且在X-三体的情况下总是自旋单线态。我们调查trions在不同的制度之间的量子限制和电子-电子相互作用的竞争，分析和数值计算。数值计算工作是在一个变分方法占整个QD边缘的电子质量不连续性。给出了三电子中电子-空穴关联的结果。讨论了不同量子点尺寸和限制势强度对束缚能的影响。
Bilayer graphene as an helical quantum Hall ferromagnet
Bernal堆叠中的双层石墨烯中的二维电子气支持整数填充因子$ν\in [-3,4].$下朗道能级N=0中的各种均匀对称性破缺基态。当在填充因子$ν=-1,3$下的层之间施加电势差（或偏压）时，基态从小偏压下的层间相干态演化到较高偏压下的轨道相干态，其中\textit{electric}偶极子与轨道赝自旋在层的平面内自发地有序。在本文中，我们表明，通过进一步增加在这两个填充因子的偏置，二维电子气首先通过Skyrmion晶体状态，然后进入螺旋状态的赝自旋在空间中旋转。Skyrmion态和螺旋态的赝自旋织构是由于在基态中存在轨道相干时，有效赝自旋哈密顿量中存在Dzyaloshinskiii-Moriya相互作用所致.我们详细研究了螺旋和Skyrmion晶体态的电子结构以及它们的集体激发，然后计算了它们的电磁吸收。
Graphene electrons feature a pair of massless Dirac cones of opposite pseudospin chirality at two valleys. Klein tunneling refers to the intriguing capability of these chiral electrons to penetrate through high and wide potential barrier. The two valleys have been treated independently in the literature, where time reversal symmetry dictates that neither the normal incidence transmission nor the angle-averaged one can have any valley polarization. Here we show that, when intervalley scattering by barrier is accounted, graphene electrons normally incident at a superlattice barrier can experienc…
Valley pseudospin, the quantum degree of freedom characterizing the degenerate valleys in energy bands, is a distinct feature of two-dimensional Dirac materials. Similar to spin, the valley pseudospin is spanned by a time reversal pair of states, though the two valley pseudospin states transform to each other under spatial inversion. The breaking of inversion symmetry induces various valley-contrasted physical properties; for instance, valley-dependent topological transport is of both scientific and technological interests. Bilayer graphene (BLG) is a unique system whose intrinsic inversion sy…
Barrier transmission of Dirac-like pseudospin-one particles
本文研究了二维T_3晶格（骰子晶格）中的势垒隧穿问题。特别是，我们专注于低能量，长波长近似的系统的哈密顿量，其中的晶格可以描述由一个Dirac-like哈密顿与赝自旋之一。增大的赝自旋S = 1（而不是石墨烯的S = 1/2）导致增强的“超级”克莱因隧穿通过矩形静电势垒。我们的结果证实了通过紧束缚模型的晶格的数值研究。对于均匀磁场，我们讨论了朗道能级，并研究了矩形磁垒的透明性。我们发现，后者主要可以描述的半经典轨道弯曲的粒子轨迹，定性类似的情况下，石墨烯。这使得可以用足够宽度的磁屏障来约束颗粒。
Observation of valley Landau-Zener-Bloch oscillations and pseudospin imbalance in photonic graphene
该研究在光诱导蜂窝晶格中观测谷间 Bloch 振荡与 Landau–Zener 隧穿，揭示对称性和梯度方向如何调控赝自旋不平衡、涡旋及谷间动力学。
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