共查询到20条相似文献，搜索用时 15 毫秒
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《Physics letters. A》2020,384(4):126094
A non-Hermitian topological insulator is fundamentally different from conventional topological insulators. The non-Hermitian skin effect arises in a nonreciprocal tight binding lattice with open edges. In this case, not only topological states but also bulk states are localized around the edges of the nonreciprocal system. We discuss that controllable switching from topological edge states into topological extended states in a chiral symmetric non-Hermitian system is possible. We show that the skin depth decreases with non-reciprocity for bulk states but increases with it for topological zero energy states. 相似文献
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We study the topological properties of a one-dimensional （1D） hardcore Bose-Fermi mixture using the exact diagonalization method. We firstly add a hardcore boson to a fermionic system and by examining the edge states we find that the quasi-particle manifests the topological properties of the system. Then we study a mixture with 7 fermions and 1 boson. We find that the mixture also exhibits topological properties and its behaviors are similar to that of the corresponding fermionic system. We present a qualitative explanation to understand such behaviors using the mapping between a hardcore boson and a spinless fermion. These results show the existence of topological properties in a 1D hardcore Bose-Fermi mixture and may be realized using cold atoms trapped in optical lattices experimentally. 相似文献
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Daniel A. Bobylev Dmitry I. Tikhonenko Dmitry V. Zhirihin Maxim Mazanov Anton Vakulenko Daria A. Smirnova Alexander B. Khanikaev Maxim A. Gorlach 《Laser u0026amp; Photonics Reviews》2023,17(1):2100567
Rapid development of topological concepts in photonics unveils exotic phenomena such as unidirectional propagation of electromagnetic waves resilient to backscattering at sharp bends and disorder-immune localization of light at stable frequencies. Recently introduced higher-order topological insulators (HOTIs) bring in additional degrees of control over light confinement and steering. However, designs of photonic HOTIs reported so far are solely exploiting lattice geometries which are hard to reconfigure thus limiting tunability. This article reports a conceptually new mechanism to engineer topological edge and corner states including higher-order topological phases which exploits both electric and magnetic responses of the meta-atoms. Hybridization between these responses gives rise to the difference in the effective coupling which is controlled by the meta-atoms mutual orientations. This feature allows to tailor photonic band topology exclusively via particle alignment and flexibly reconfigure the topological phase. Focusing on the kagome array of split-ring resonators, the topological edge and corner states are experimentally demonstrated in the microwave domain. To highlight the generality of this proposal, the formation of higher-order topological phase is also predicted numerically in a C6-symmetric lattice of split-ring resonators. These findings provide a new promising route to induce and control higher-order topological phases and states. 相似文献
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《Physics letters. A》2019,383(22):2567-2570
We consider an N-level non-Hermitian Hamiltonian with an exceptional point of order N. We define adiabatic equivalence in such systems and explore topological phase. We show that the topological exceptional states appear at the interface of topologically distinct systems. We discuss that topological states appear even in closed systems. We explore dynamical robustness of exceptional edge states. 相似文献
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《Laser u0026amp; Photonics Reviews》2018,12(8)
Topological insulators are unique devices supporting unidirectional edge states at their interfaces. Due to topological protection, such edge states persist in the presence of disorder and do not experience backscattering upon interaction with defects. Despite the topological protection and the fact that such states at the opposite edges of an insulator carry opposite currents, a physical mechanism exists allowing topological excitations propagating at opposite edges to be resonantly coupled. Such a mechanism uses weak periodic temporal modulations of the system parameters and does not affect the internal symmetry and topology of the system. This mechanism is illustrated in truncated honeycomb arrays of microcavity pillars, where topological insulation is possible for polaritons under the combined action of spin–orbit coupling and Zeeman splitting in the external magnetic field. The temporal modulation of the potential leads to a periodic switching between topological states with the same Bloch momentum, but located at the opposite edges. The switching rate is found to increase for narrower ribbon structures and for larger modulation depth, though it is changing nonmonotonically with the Bloch momentum of the input edge state. These results provide a promising realization of a coupling device based on topologically protected states. 相似文献
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Xiaoxiao Wu Zhenyu Li Jian Chen Xin Li Jingxuan Tian Yingzhou Huang Shuxia Wang Weixin Lu Bo Hou Che Ting Chan Weijia Wen 《Advanced Optical Materials》2019,7(20)
Valley‐Hall phases, first proposed in 2D materials, originate from nontrivial topologies around valleys which denote local extrema in momentum space. Since they have been extended into classical systems, their designs draw inspirations from existing quantum counterparts, and their transports show similar topological protections. In contrast, it has been recently established in acoustics that layer pseudospins in valley‐Hall phases can give rise to special valley‐Hall edge states with fundamentally different transport behaviors at the interfaces compared with various 2D materials. Their realization in other classical systems, such as photonics, would allow to design topological insulators beyond quantum inspirations. Here, it is shown that layer pseudospins exist in photonic valley‐Hall phases, using vertically coupled designer surface plasmon crystals, a nonradiative system in open environment supporting tightly confined propagating modes. The negligible thermal and radiative losses in the structure pave the way for the direct observations of the layer pseudospins and associated topological phenomena stem from them in both real and reciprocal spaces. Photonic devices that manipulate the signals based on the layer pseudospins of the topological phases, such as layer convertors and layer‐selected delay lines, are experimentally demonstrated, confirming the potential applications of the layer pseudospins as a new degree of freedom carrying information. 相似文献
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Jiabin Li Pan Zhou Zhengchun Zou Rui Tan Lizhong Sun Kaiwang Zhang 《physica status solidi b》2020,257(9):2000010
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Robust multiband photonic topological edge states are of great importance for photonic applications, including nonlinear wavelength conversion. In particular, higher-order photonic topological states provide the realizability of photonic nanoresonators with high robustness against structural disorder of photonic crystals. This work reveals that multiband photonic topological valley-Hall edge states and second-order corner states can be observed in square lattice photonic crystals consisting of triangular dielectric rods. For small sizes of the triangles, multiband gapless edge modes propagate through the photonic topological waveguide. Their transmission characteristics and robustness against the structural defects have been evaluated for linear and Z-shaped interfaces. When the size of the triangles increases, most of edge bands become gapped and one can obtain disorder-immune multiband second-order topological corner states, which is the core result of this report. The results obtained in this work can find important applications for nonlinear topological frequency conversion. 相似文献
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拓扑绝缘体是当前凝聚态物理研究的热点.退相干效应对该体系的影响的研究不仅有重要的理论意义,而且也是实现未来量子器件的不可或缺的前期工作.文章作者从理论上研究了退相干对二维拓扑绝缘体特别是量子自旋霍尔效应的影响.研究结果表明,作为量子自旋霍尔效应的标志的量子化纵向电阻平台对不破坏自旋记忆的退相干效应（普通退相干）不敏感,但却对破坏自旋记忆的退相干效应（自旋退相干）非常敏感.因此,该量子化平台只能在尺寸小于自旋退相干长度的介观样品中存在,从而解释了量子自旋霍尔效应实验中所观测到的结果(见Science ,20 相似文献
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C. W. J. Beenakker A. Donís Vela G. Lemut M. J. Pacholski J. Tworzydło 《Annalen der Physik》2023,535(7):2300081
Methods to discretize the Hamiltonian of a topological insulator or topological superconductor, without giving up on the topological protection of the massless excitations (respectively, Dirac fermions or Majorana fermions) are reviewed. The method of tangent fermions, pioneered by Richard Stacey, is singled out as being uniquely suited for this purpose. Tangent fermions propagate on a dimensional space-time lattice with a tangent dispersion: in dimensionless units. They avoid the fermion doubling lattice artefact that will spoil the topological protection, while preserving the fundamental symmetries of the Dirac Hamiltonian. Although the discretized Hamiltonian is nonlocal, as required by the fermion-doubling no-go theorem, it is possible to transform the wave equation into a generalized eigenproblem that is local in space and time. Applications that are discussed include Klein tunneling of Dirac fermions through a potential barrier, the absence of localization by disorder, the anomalous quantum Hall effect in a magnetic field, and the thermal metal of Majorana fermions. 相似文献
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K. A. Kolwas G. Grabecki S. Trushkin J. Wrbel M. Aleszkiewicz &#x;. Cywi&#x;ski T. Dietl G. Springholz G. Bauer 《physica status solidi b》2013,250(1):37-47
We report on experiments allowing to set an upper limit on the magnitude of the spin Hall effect and the conductance by edge channels in quantum wells of PbTe embedded between PbEuTe barriers. We reexamine previous data obtained for epitaxial microstructures of n‐type PbSe and PbTe, in which pronounced nonlocal effects and reproducible magnetoresistance oscillations were found. Here we show that these effects are brought about by a quasi‐periodic network of threading dislocations adjacent to the BaF2 substrate, which give rise to a p‐type interfacial layer and an associated parasitic parallel conductance. We then present results of transport measurements on microstructures of modulation doped PbTe/(Pb,Eu)Te:Bi heterostructures for which the influence of parasitic parallel conductance is minimized, and for which quantum Hall transport had been observed, on similar samples, previously. These structures are of H‐shaped geometry and they are patterned of 12 nm thick strained PbTe quantum wells embedded between Pb0.92Eu0.08Te barriers. The structures have different lateral sizes corresponding to both diffusive and ballistic electron transport in non‐equivalent L valleys. For these structures no nonlocal resistance is detected confirming that PbTe is a trivial insulator. The magnitude of spin Hall angle γ is estimated to be smaller than 0.02 for PbTe/PbEuTe microstructures in the diffusive regime. 相似文献
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拓扑绝缘体是当前凝聚态物理研究的热点.退相干效应对该体系的影响的研究不仅有重要的理论意义,而且也是实现未来量子器件的不可或缺的前期工作.文章作者从理论上研究了退相干对二维拓扑绝缘体特别是量子自旋霍尔效应的影响.研究结果表明,作为量子自旋霍尔效应的标志的量子化纵向电阻平台对不破坏自旋记忆的退相干效应(普通退相干)不敏感,但却对破坏自旋记忆的退相干效应(自旋退相干)非常敏感.因此,该量子化平台只能在尺寸小于自旋退相干长度的介观样品中存在,从而解释了量子自旋霍尔效应实验中所观测到的结果(见Science,2007,318:766).同时,文章作者还定义了一个新的物理量,即自旋霍尔电阻,并发现该自旋霍尔电阻也有量子化平台.特别是该量子化平台对两种类型的退相干都不敏感.这说明在宏观样品中也能观测到自旋霍尔电阻的量子化平台,因此更能全面地反映量子自旋霍尔效应的拓扑特性. 相似文献
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Chengyong Zhong 《Frontiers of Physics》2021,16(6):63503
Three-dimensional (3D) topological insulators (TIs) have been studied for approximately fifteen years, but those made from group-IV elements, especially Ge and Sn, seem particularly attractive owing to their nontoxicity, sizable intrinsic spin–orbit coupling (SOC) strength and natural compatibility with the current semiconductor industry. However, group-IV elemental TIs have rarely been reported, except for the low temperature phase of α-Sn under strain. Here, based on first-principles calculations, we propose new allotropes of Ge and Sn, named T5-Ge/Sn, as desirable TIs. These new allotropes are also highly anisotropic Dirac semimetals if the SOC is turned off. To the best of our knowledge, T5-Ge/Sn are the first 3D allotropes of Ge/Sn that possess topological states in their equilibrium states at room temperature. Additionally, their isostructures of C and Si are metastable indirect and direct semiconductors. Our work not only reveals two promising TIs, but more profoundly, we justify the advantages of group-IV elements as topological quantum materials (TQMs) for fundamental research and potential practical applications, and thus reveal a new direction in the search for desirable TQMs. 相似文献
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Xiaoxiao Wang;Ruizhe Gu;Yandong Li;Huixin Qi;Xiaoyong Hu;Qihuang Gong; 《Laser u0026amp; Photonics Reviews》2024,18(1):2300204
Higher-order topological insulators hosting topological modes at hinges and corners provide a new avenue for disorder-immune light transport, which prospects great potential in applications of integrated photonics devices. However, the active control of topological modes in 3D higher-order topological insulators is not realized yet, and its construction is too complicated and huge to analyze. Here, a method is proposed to construct effective Hamiltonians for higher-order topological insulators, which provides a correct physical picture of the states and the corresponding energies at the domain walls. A non-Hermitian 3D honeycomb lattice is constructed, which can generate arbitrary-located, arbitrary-shaped, and robust topological hinge states propagating at gain-loss domain walls. The 3D honeycomb lattice can also appear as non-Hermitian third-order TIs exhibiting corner states, which can be dynamically controlled and show new topologically protected confinement rules. This work expands the understanding of the topological properties in non-Hermitian systems and enables the dynamic control of topological states of different dimensions. 相似文献
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Su-Schreiffer-Heeger模型预测了在一维周期晶格的边缘处可能出现零维的拓扑零能模,其能量本征值总是出现在能隙的正中间.本文以半导体微腔阵列中光子和激子在强耦合情况下形成的准粒子为例,通过准粒子的自旋轨道耦合与Zeeman效应,研究了时间反演对称性破缺对拓扑零能模的影响.发现拓扑零能模的能量本征值可以随着自旋轨道耦合强度的变化在整个带隙内移动,自旋相反的模式移动方向相反;在二维微腔阵列中发现了沿着晶格边缘移动的拓扑零能模,提出了一维零能模的概念.由于时间反演对称性的破缺,这种一维拓扑零能模解除了在相反传输方向上的能级的简并,从而在传输过程中出现极强的绕过障碍物的能力. 相似文献
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Weifeng Zhang Xianfeng Chen Yaroslav V. Kartashov Dmitry V. Skryabin Fangwei Ye 《Laser u0026amp; Photonics Reviews》2019,13(11)
Photonic topological insulators supporting unidirectional topologically protected edge states represent an attractive platform for the realization of disorder‐ and backscattering‐immune transport of edge excitations in both linear and nonlinear regimes. While the properties of the edge states at unclosed interfaces of two bulk media with different topologies are known, the existence of edge states in practical finite‐dimensional topological insulators fully immersed in a nontopological environment remains largely unexplored. In this work, using realistic polariton topological insulators built from small‐size honeycomb arrays of microcavity pillars as an example, it is shown how topological properties of the system build up upon gradual increase of its dimensionality. To account for the dissipative nature of the polariton condensate forming in the array of microcavity pillars, the impact of losses and resonant pump leading to rich bistability effects in this system is considered. The mechanism is described in accordance with which trivial‐phase pump “selects” and excites specific nonlinear topological edge states circulating along the periphery of the structure in the azimuthal direction, dictated by the direction of the external applied magnetic field. The possibility of utilization of vortex pump with different topological charges for selective excitation of different edge currents is also shown. 相似文献