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DECaNT: Simulation tool for diffusion of excitons in carbon nanotube films DECaNT:碳纳米管薄膜中激子扩散的模拟工具
Pub Date : 2020-10-22 DOI: 10.1063/5.0034600
S. Belling, Y. C. Li, A. Davoody, A. Gabourie, I. Knezevic
We present the numerical tool DECaNT (Diffusion of Excitons in Carbon NanoTubes) that simulates exciton transport in thin films of carbon nanotubes. Through a mesh of nanotubes generated using the Bullet Physics C++ library, excitons move according to an ensemble Monte Carlo algorithm, with the scattering rates that account for tube chirality, orientation, and distance. We calculate the diffusion tensor from the position--position correlation functions and analyze its anisotropy and dependence on the film composition, morphology, and defect density.
我们提出了一个数值工具DECaNT(激子在碳纳米管中的扩散)来模拟激子在碳纳米管薄膜中的传输。通过使用Bullet Physics c++库生成的纳米管网格,激子根据集合蒙特卡罗算法移动,散射率决定了管的手性、方向和距离。我们从位置-位置相关函数中计算扩散张量,并分析其各向异性以及对薄膜成分、形貌和缺陷密度的依赖。
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引用次数: 0
Disorder effects of vacancies on the electronic transport properties of realistic topological insulator nanoribbons: The case of bismuthene 空位对实际拓扑绝缘体纳米带电子输运性质的无序影响:以铋为例
Pub Date : 2020-10-22 DOI: 10.1103/PHYSREVMATERIALS.5.014204
A. Pezo, B. Focassio, G. R. Schleder, M. Costa, C. Lewenkopf, A. Fazzio
The robustness of topological materials against disorder and defects is presumed but has not been demonstrated explicitly in realistic systems. In this work, we use state-of-the-art density functional theory and recursive nonequilibrium Green's functions methods to study the effect of disorder in the electronic transport of long nanoribbons, up to 157 nm, as a function of vacancy concentration. In narrow nanoribbons, even for small vacancy concentrations, defect-like localized states give rise to hybridization between the edge states erasing topological protection and enabling backscattering events. We show that the topological protection is more robust for wide nanoribbons, but surprisingly it breaks down at moderate structural disorder. Our study helps to establish some bounds on defective bismuthene nanoribbons as promising candidates for spintronic applications.
拓扑材料对无序和缺陷的鲁棒性是假定的,但尚未在现实系统中得到明确的证明。在这项工作中,我们使用最先进的密度泛函理论和递归非平衡格林函数方法研究了长纳米带(高达157 nm)电子输运中无序作为空位浓度的函数的影响。在狭窄的纳米带中,即使空位浓度很小,缺陷类局域态也会导致边缘态之间的杂化,从而消除拓扑保护并使后向散射事件成为可能。我们发现拓扑保护对于宽的纳米带是更稳健的,但令人惊讶的是,它在适度的结构紊乱时破坏。我们的研究有助于建立缺陷铋纳米带作为自旋电子应用的有希望的候选者的一些界限。
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引用次数: 13
Topological correspondence between magnetic space group representations and subdimensions 磁空间群表示与子维之间的拓扑对应关系
Pub Date : 2020-10-20 DOI: 10.1103/PhysRevB.103.245127
Adrien Bouhon, Gunnar F. Lange, Robert-Jan Slager
The past years have seen rapid progress in the classification of topological band structures using symmetry eigenvalue indicated methods. Given their importance in condensed matter systems, these ideas are increasingly getting explored in the pertinent context of magnetic structures. We here adopt this viewpoint to address the physical implications of extending space groups to magnetic variants. In particular, we introduce a simple model as a generic example of magnetic fragile topology. Most interestingly, we find that this antiferromagnetic-compatible model can be tuned via Zeeman terms to a ferro/ferrimagnetic (FM) counterpart in the same space-group family. This correspondence manifests itself by ensuring that the fragile topology produces bands of finite Chern number in the FM phase. In addition, we discuss how the system can be tuned into a stable topological semimetallic phase, characterized by a simple expression for the $mathbf{Z}_2$ symmetry indicator that results from the combination of $C_4$ symmetry and $C_2T$-protected Euler class topology. This scenario features a similar correspondence that can even relate to higher Chern numbers. Pointing out the generality of such relations for a variety of space group families, we believe our results pave the way for new pursuits in magnetic topologies.
近年来,利用对称特征值表示方法对拓扑带结构进行分类的研究进展迅速。鉴于它们在凝聚态体系中的重要性,这些想法越来越多地在磁性结构的相关背景下得到探索。我们在这里采用这一观点来解决将空间群扩展到磁变体的物理含义。特别地,我们介绍了一个简单的模型作为磁性脆性拓扑的一般例子。最有趣的是,我们发现这种反铁磁兼容模型可以通过塞曼项调谐到同一空间群族中的铁/铁磁(FM)对应。这种对应关系通过确保脆弱拓扑在FM相位产生有限陈氏数的频带而表现出来。此外,我们讨论了如何将系统调谐到稳定的拓扑半金属相,其特征是由$C_4$对称和$C_2T$保护的欧拉类拓扑组合而成的$mathbf{Z}_2$对称指示符的简单表达式。这个场景具有类似的对应关系,甚至可以与更高的陈氏数相关。指出这种关系对各种空间群族的普遍性,我们相信我们的结果为磁拓扑的新追求铺平了道路。
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引用次数: 35
Ambipolar magneto-optical response of ultralow carrier density topological insulators 超低载流子密度拓扑绝缘体的双极性磁光响应
Pub Date : 2020-10-20 DOI: 10.1103/PHYSREVB.103.L081110
D. Chaudhuri, M. Salehi, S. Dasgupta, Mintu Mondal, J. Moon, D. Jain, Seongshik Oh, N. P. Armitage
We have investigated the THz range magneto-optical response of ultralow carrier density films of Sb$_2$Te$_3$ using time-domain THz polarimetry. Undoped Sb$_2$Te$_3$ has a chemical potential that lies inside the bulk valence band. Thus its topological response is masked by bulk carriers. However, with appropriate buffer layer engineering and chemical doping, Sb$_2$Te$_3$ thin films can be grown with extremely low electron or hole densities. The ultralow carrier density samples show unusual optical properties and quantized response in the presence of magnetic fields. Consistent with the expectations for Dirac fermions, a quantized Hall response is seen even in samples where the zero field conductivity falls below detectable levels. The discontinuity in the Faraday angle with small changes in the filling fraction across zero is manifestation of the parity anomaly in 2D Dirac systems with broken time reversal symmetry.
用时域太赫兹偏振法研究了Sb$_2$Te$_3$超低载流子密度薄膜的太赫兹磁光响应。未掺杂的Sb$_2$Te$_3$的化学势位于体价带内。因此,它的拓扑响应被散货船所掩盖。然而,通过适当的缓冲层工程和化学掺杂,可以在极低的电子或空穴密度下生长出Sb$_2$Te$_3$薄膜。超低载流子密度样品在磁场作用下表现出不同寻常的光学特性和量子化响应。与对狄拉克费米子的预期一致,即使在零场电导率低于可检测水平的样品中,也可以看到量子化的霍尔响应。法拉第角的不连续和过零填充分数的微小变化是时间反转对称性破坏的二维狄拉克系统奇偶异常的表现。
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引用次数: 3
Theory of the low-temperature longitudinal spin Seebeck effect 低温纵向自旋塞贝克效应理论
Pub Date : 2020-10-19 DOI: 10.1103/PHYSREVB.103.014412
R. Schmidt, P. Brouwer
Using a simplified microscopic model of coupled spin and lattice excitations in a ferromagnetic insulator we evaluate the magnetic-field dependence of the spin Seebeck effect at low temperatures. The model includes Heisenberg exchange coupling, a harmonic lattice potential, and a pseudo-dipolar exchange interaction. Our approach goes beyond previous work [Phys. Rev. B 98, 134421 (2018)] in that it does not rely on the a priori assumption of a fast equilibration of the magnon and phonon distributions. Our theory shows that singular features in the magnetic-field dependence of the spin Seebeck effect at low temperatures observed by Kikkawa et al. [Phys. Rev. Lett. 117, 207203 (2016)] are independent of the relative strength of magnon-impurity and phonon-impurity scattering.
利用铁磁绝缘体中自旋和晶格耦合的简化微观模型,研究了低温下自旋塞贝克效应对磁场的依赖性。该模型包括海森堡交换耦合、调和晶格势和伪偶极交换相互作用。我们的方法超越了以前的工作[物理学]。Rev. B . 98, 134421(2018)],因为它不依赖于磁振子和声子分布快速平衡的先验假设。我们的理论显示了Kikkawa等人在低温下观察到的自旋塞贝克效应的磁场依赖性的奇异特征。与磁非杂质散射和声子杂质散射的相对强度无关。
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引用次数: 2
Tuning resonance energy transfer with magneto-optical properties of graphene 石墨烯磁光特性调谐共振能量转移
Pub Date : 2020-10-19 DOI: 10.1103/PhysRevB.103.174421
P. Abrantes, G. Bastos, D. Szilard, C. Farina, F. Rosa
We investigate the resonance energy transfer (RET) rate between two quantum emitters near a suspended graphene sheet in vacuum under the influence of an external magnetic field. We perform the analysis for low and room temperatures and show that, due to the extraordinary magneto-optical response of graphene, it allows for an active control and tunability of the RET even in the case of room temperature. We also demonstrate that the RET rate is extremely sensitive to small variations of the applied magnetic field, and can be tuned up to a striking six orders of magnitude for quite realistic values of magnetic field. Moreover, we evidence the fundamental role played by the magnetoplasmon polaritons supported by the graphene monolayer as the dominant channel for the RET within a certain distance range. Our results suggest that magneto-optical media may take the manipulation of energy transfer between quantum emitters to a whole new level, and broaden even more its great spectrum of applications.
我们研究了在外部磁场的影响下,真空中悬浮石墨烯片附近两个量子发射体之间的共振能量转移(RET)速率。我们在低温和室温下进行了分析,结果表明,由于石墨烯非凡的磁光响应,即使在室温下,也可以对RET进行主动控制和可调性。我们还证明了RET率对外加磁场的微小变化非常敏感,并且可以调到惊人的六个数量级,以获得相当现实的磁场值。此外,我们证明了在一定距离范围内,石墨烯单层支持的磁等离子激元极化子作为RET的主要通道发挥了基本作用。我们的研究结果表明,磁光介质可以将量子发射体之间的能量转移操纵提升到一个全新的水平,并进一步扩大其广泛的应用范围。
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引用次数: 2
Theory of the Strain Engineering of Graphene Nanoconstrictions 石墨烯纳米缩窄的应变工程理论
Pub Date : 2020-10-19 DOI: 10.7566/JPSJ.90.023701
M. Hayashi, H. Yoshioka, H. Tomori, A. Kanda
Strain engineering is one of the key technologies for using graphene as an electronic device: the strain-induced pseudo-gauge field reflects Dirac electrons, thus opening the so-called conduction gap. Since strain accumulates in constrictions, graphene nanoconstrictions can be a good platform for this technology. On the other hand, in the graphene nanoconstrictions, Fabry-Perot type quantum interference dominates the electrical conduction at low bias voltages. We argue that these two effects have different strain dependence; the pseudo-gauge field contribution is symmetric with respect to positive (tensile) and negative (compressive) strain, whereas the quantum interference is antisymmetric. As a result, a peculiar strain dependence of the conductance appears even at room temperatures.
应变工程是利用石墨烯作为电子器件的关键技术之一:应变诱导的伪规范场反映狄拉克电子,从而打开所谓的传导间隙。由于应变在收缩中积累,石墨烯纳米收缩可以成为该技术的良好平台。另一方面,在石墨烯纳米结构中,法布里-珀罗型量子干涉在低偏置电压下主导导电。我们认为这两种效应具有不同的应变依赖性;伪规范场的贡献相对于正(拉伸)和负(压缩)应变是对称的,而量子干涉是反对称的。因此,即使在室温下,电导也会出现特殊的应变依赖关系。
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引用次数: 0
Fabry-Pérot resonant vortices and magnetoconductance in topological insulator constrictions with magnetic barriers 具有磁障的拓扑绝缘体缩窄中的法布里-帕氏共振涡和磁导
Pub Date : 2020-10-19 DOI: 10.1103/PhysRevB.103.205124
R. P. Maciel, A. L. Ara'ujo, C. Lewenkopf, G. J. Ferreira
The edge states of two-dimensional time-reversal topological insulators (TIs) support a perfect helical conductance on wide ribbons due to the absence of backscattering. Here, we study the changes in the transport properties of TI nanoribbons by introducing a constriction along the ribbon. This set up allows the edge states to hybridize, leading to reflections at the ends of the constriction. We find that the electronic states running along one edge can be reflected back along the opposite edge multiple times, giving rise to Fabry-Perot resonant vortexes within the constriction with well defined conductance peaks. We show that magnetic barriers allow one to manipulate these peaks and obtain significant changes in the system spin-resolved magnetoconductance.
由于不存在后向散射,二维时间反转拓扑绝缘体的边缘态在宽带状上支持完美的螺旋电导。在这里,我们研究了TI纳米带的输运性质的变化,通过引入沿带的收缩。这种设置允许边缘状态杂交,导致收缩末端的反射。我们发现沿一个边缘运行的电子态可以沿另一个边缘多次反射回来,在收缩内产生具有明确电导峰的法布里-佩罗共振涡。我们表明,磁屏障允许人们操纵这些峰,并获得系统自旋分辨磁导的显著变化。
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引用次数: 4
Quantum network approach to spin interferometry driven by Abelian and non-Abelian fields 阿贝尔场和非阿贝尔场驱动自旋干涉的量子网络方法
Pub Date : 2020-10-16 DOI: 10.1103/PHYSREVB.103.155419
A. Hijano, T. L. van den Berg, D. Frustaglia, D. Bercioux
We present a theory of conducting quantum networks that accounts for Abelian and non-Abelian fields acting on spin carriers. We apply this approach to model the conductance of mesoscopic spin interferometers of different geometry (such as squares and rings), reproducing recent experimental findings in pattered InAsGa quantum wells subject to Rashba spin-orbit and Zeeman fields. Moreover, by introducing some additional field-texture engineering, we manage to single out a previously unnoticed spin-phase suppression mechanisms. We observe that our approach also applies to the study of complex networks and the spectral properties of closed systems.
我们提出了一种解释作用于自旋载流子上的阿贝尔场和非阿贝尔场的传导量子网络理论。我们将这种方法应用于模拟不同几何形状(如正方形和环状)的介观自旋干涉仪的电导,再现了最近在Rashba自旋轨道和Zeeman场作用下的图案InAsGa量子阱中的实验结果。此外,通过引入一些额外的场织构工程,我们成功地挑出了以前未被注意到的自旋相位抑制机制。我们观察到,我们的方法也适用于研究复杂网络和封闭系统的频谱特性。
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引用次数: 4
Long-lived dark coherence brought to light by magnetic-field controlled photon echo 磁场控制光子回波带来的长寿命暗相干
Pub Date : 2020-10-16 DOI: 10.1103/PhysRevB.103.235312
I. A. Solovev, I. I. Yanibekov, Y. Efimov, S. A. Eliseev, V. A. Lovcjus, I. Yugova, S. Poltavtsev, Y. Kapitonov
Larmor precession of the quasiparticle spin about a transverse magnetic field leads to the oscillations in the spontaneous photon echo signal due to the shuffling of the optical coherence between optically accessible (bright) and inaccessible (dark) states. Here we report on a new non-oscillating photon echo regime observed in the presence of non-equal dephasing rates of bright and dark states. This regime enables the observation of the long-living dark optical coherence. As a simple mechanical analogy, we suggest a charged particle moving in the magnetic field through the medium with anisotropic viscous friction. We demonstrate the dark coherence retrieval in the spontaneous photon echo from excitons in the InGaAs/GaAs quantum well.
准粒子自旋沿横向磁场的拉莫尔进动导致自发光子回波信号的振荡,这是由于光学相干性在光学可达(亮)态和不可达(暗)态之间的变换。在这里,我们报告了一种新的非振荡光子回波制度,观察到在存在非相等的光和暗状态的减相率。这种状态使得观测长寿命的暗光学相干成为可能。作为一个简单的力学类比,我们提出一个带电粒子在磁场中通过具有各向异性粘性摩擦的介质运动。研究了InGaAs/GaAs量子阱中激子自发光子回波的暗相干恢复。
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引用次数: 2
期刊
arXiv: Mesoscale and Nanoscale Physics
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