Nonlinearity induced topological properties in nonlinear lattice systems are studied in both momentum space and real space. Experimentally realizable through the Kerr effect on photonic waveguide systems, our working model depicts on-site nonlinearity added to the Su-Schrieffer-Heeger (SSH) model plus a chiral-symmetry breaking term. Under the periodic-boundary condition, two of the nonlinear energy bands approach the energy bands of the chiral-symmetric SSH model as nonlinearity strength increases. Further, we account for a correction to the Zak phase and obtain a general expression for nonlinear Zak phases. For sufficiently strong nonlinearity, the sum of all nonlinear Zak phases (not the sum of all conventional Zak phases) is found to be quantized. In real space, it is discovered that there is a strong interplay between nonlinear solitons and the topologically protected edge states of the associated chiral-symmetric linear system. Nonlinearity can recover the degeneracy between two edge soliton states, albeit a chiral-symmetry breaking term. We also reveal the topological origin of in-gap solitons even when the associated linear system is in the topological trivial regime. These momentum-space and real-space results have clearly demonstrated new topological features induced by nonlinearity, indicating that topological physics in nonlinear lattice systems is far richer than previously thought.
We study the topological physics in nonlinear Schrödinger systems on lattices. We employ the quench dynamics to explore the phase diagram, where a pulse is given to a lattice point and we analyze its time evolution. There are two system parameters $λ$ and $ξ$, where $λ$ controls the hoppings between the neighboring links and $ξ$ controls the nonlinearity. The dynamics crucially depends on these system parameters. Based on analytical and numerical studies, we derive the phase diagram of the nonlinear Su-Schrieffer-Heeger (SSH) model in the ($λ,ξ$) plane. It consists of four phases. The topologi…
A new design paradigm of topology has recently emerged to manipulate the flow of phonons. At its heart lies a topological transition to a nontrivial state with exotic properties. This framework has been limited to linear lattice dynamics so far. Here we show a topological transition in a nonlinear regime and its implication in emerging nonlinear solutions. We employ nonlinearity management such that the system consists of masses connected with two types of nonlinear springs, "stiffening" and "softening" types, alternating along the length. We show, analytically and numerically, that the lattic…
Nonlinearity-driven Topology via Spontaneous Symmetry Breaking
Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche（复杂系统研究所，意大利国家研究委员会）；Physics Department, University of Rome, “La Sapienza”（罗马大学“萨皮恩扎”物理系）；Université Paris Cité, CNRS, Matériaux et Phénomènes Quantiques（巴黎西岱大学，法国国家科学研究中心，物质与量子现象实验室）
The interplay of nonlinearity and topology results in many novel and emergent properties across a number of physical systems such as chiral magnets, nematic liquid crystals, Bose-Einstein condensates, photonics, high energy physics, etc. It also results in a wide variety of topological defects such as solitons, vortices, skyrmions, merons, hopfions, monopoles to name just a few. Interaction among and collision of these nontrivial defects itself is a topic of great interest. Curvature and underlying geometry also affect the shape, interaction and behavior of these defects. Such properties can b…
We investigate the topological physics and the nonlinearity-induced trap phenomenon in a coupled system of pendulums. It is described by the dimerized sine-Gordon model, which is a combination of the sine-Gordon model and the Su-Schrieffer-Heeger model. The initial swing angle of the left-end pendulum may be regarded as the nonlinearity parameter. The topological number is well defined as far as the pendulum is approximated by a harmonic oscillator. The emergence of the topological edge state is clearly observable in the topological phase by solving the quench dynamics starting from the left-e…
In this work we explore the effects of nonlinearity on three-dimensional topological phases. Of particular interest are the so-called Weyl semimetals, known for their Weyl nodes, i.e., point-like topological charges which always exist in pairs and demonstrate remarkable robustness against general perturbations. It is found that the presence of onsite nonlinearity causes each of these Weyl nodes to break down into nodal lines and nodal surfaces at two different energies while preserving its topological charge. Depending on the system considered, additional nodal lines may further emerge at high…
Topological edge states are known to emerge in certain quasicrystals. We investigate a topological quasicrystal in the presence of nonlinearity by generalizing the Toda lattice to include modulated periodic hoppings, where the period is taken irrational to the original lattice. It is found that topological edge states in a quasicrystal survive against nonlinearity based on the quench dynamics. It is also found that an extended-localization transition is induced by the quasicrystal hopping modulation. The present model is experimentally realizable by a transmission line with variable capacitanc…
A salient feature of solid-state topological materials in two dimensions is the presence of conducting electronic edge states that are insensitive to scattering by disorder. Such unidirectional edge states have been explored in many experimental settings beyond solid-state electronic systems, including in photonic devices, mechanical and acoustic structures, and others. It is of great interest to understand how topological states behave in the presence of inter-particle interactions and nonlinearity. Here we experimentally demonstrate unidirectional soliton-like nonlinear states on the edge of…
We study general features of the excitation spectrum of a system of one-dimensional chiral spinless fermions with short-range interactions. We show that the nature of the elementary excitations of such a system depends strongly on the nonlinearity of the underlying dispersion of the fermions. In the case of quadratic nonlinearity, the low-momentum excitations are essentially fermionic quasiparticles and quasiholes, whereas the high-momentum ones are classical harmonic waves and solitons. In the case of cubic nonlinearity, the nature of the elementary excitations does not depend on momentum and…
We report localized and unidirectional nonlinear traveling edge waves discovered theoretically and numerically in a 2D mechanical (phononic) topological insulator. The lattice consists of a collection of pendula with weak Duffing nonlinearity connected by linear springs. We show that the classical 1D nonlinear Schrodinger equation governs the envelope of 2D edge modes, and study the propagation of traveling waves and rogue waves in 1D as edge solitons in 2D. As a result of topological protection, these edge solitons persist over long time intervals and through irregular boundaries.
The momentum and spin of charge carriers in the topological insulators are constrained to be perpendicular to each other due to the strong spin-orbit coupling. We have investigated this unique spin-momentum locking property in Sb2Te3 topological insulator nanowires by injecting spin-polarized electrons through magnetic tunnel junction electrodes. Non-local voltage measurements exhibit a symmetry with respect to the magnetic field applied perpendicular to the nanowire channel, which is remarkably different from that of a non-local measurement in a channel that lacks spin-momentum locking. In st…
Emergent Momentum-Space Skyrmion Texture on the Surface of Topological Insulators
在磁性拓扑绝缘体中，量子反常霍尔效应已被理论预言和实验证实。此外，这些材料的表面态在动量空间中表现出类似刺猬的“自旋”织构。在这里，我们应用先前制定的低能量模型Bi $_2$ Se $_3$，一个母体化合物的磁性拓扑绝缘体，一个平板的几何形状中，交换场的行为只在一个表面层。在这个示例设置中，刺猬变换为临界交换场之外的skyrmion纹理。这个临界场标志着两个拓扑上不同的阶段之间的过渡。拓扑相变发生时，费米能级处的能隙没有闭合，横向霍尔电导保持不变，并量子化为$e^2/2h$。动量空间Skyrmion结构在有限的场范围内持续存在。它可以在具有三维拓扑绝缘体和铁磁绝缘体之间的界面的混合异质结构中找到其实现。
Scattering properties of the three-dimensional topological insulator Sb2Te3: Coexistence of topologically trivial and non-trivial surface states with opposite spin-momentum helicity
二元硫族化合物Bi 2 Te 3和Bi 2 Se 3是研究最广泛的拓扑绝缘体。虽然最近在磁性掺杂的Sb 2 Te 3中观察到量子反常霍尔效应，但对该化合物的研究程度要小得多。在这里，通过使用能量分辨准粒子干涉映射，我们调查的原始Sb2Te3表面的散射事件。我们发现，除了狄拉克费米子，另一个强自旋极化的表面共振出现在更高的能量在未占领的电子状态。虽然这两个表面状态是不同的起源，即拓扑保护和平凡的，分别，都表现出强烈的方向性散射特性和没有背散射。与从头计算结果的比较表明，这是一个直接的后果，他们的自旋动量锁定自旋织构被发现表现出相反的转动意义的平凡态和狄拉克态。
Topological properties of materials, as manifested in the intriguing phenomena of quantum Hall effect and topological insulators, have attracted overwhelming transdisciplinary interest in recent years. Topological edge states, for instance, have been realized in versatile systems including electromagnetic-waves. Typically, topological properties are revealed in momentum space, using concepts such as Chern number and Berry phase. Here, we demonstrate a universal mapping of the topology of Dirac-like cones from momentum space to real space. We evince the mapping by exciting the cones in photonic…
Nonequilibrium quantum dynamics of many-body systems is the frontier of condensed matter physics; recent advances in various time-resolved spectroscopic techniques continue to reveal rich phenomena. Angle-resolved photoemission spectroscopy (ARPES) as one powerful technique can resolve electronic energy, momentum, and spin along the time axis after excitation. However, dynamics of spin textures in momentum space remains mostly unexplored. Here we demonstrate theoretically that the photoexcited surface state of genuine or magnetically doped topological insulators shows novel topological spin te…
Higher-order topological phases (HOTPs) are characterized by symmetry-protected bound states at the corners or hinges of the system. In this work, we reveal a momentum-space counterpart of HOTPs in time-periodic driven systems, which are demonstrated in a two-dimensional extension of the quantum double-kicked rotor. The found Floquet HOTPs are protected by chiral symmetry and characterized by a pair of topological invariants, which could take arbitrarily large integer values with the increase of kicking strengths. These topological numbers can also be measured from the chiral dynamics of wave …
Slow-light waveguides can strongly enhance light-matter interaction, but suffer from narrow bandwidth, increased backscattering, and Anderson localization. Edge states in photonic topological insulators resist backscattering and localization, but typically cross the bandgap over a single Brillouin zone, meaning that slow group velocity implies narrow-band operation. Here we show theoretically that this can be circumvented via an edge termination that causes the edge state to wind many times around the Brillouin zone, making it both slow and broadband.
Novel classical wave phenomenon analogs of the quantum spin Hall effect are mostly based on the construction of pseudo-spins. Here we show that the non-trivial topology of a system can also be realized using orbital angular momentum through angular-momentum-orbital coupling. The idea is illustrated with a tight-binding model and experimentally demonstrated with a transmission line network. We show experimentally that even a very small network cluster exhibits one-way topological edge states, and their properties can be described in terms of local Chern numbers. Our work provides a new mechanis…
First observation of Spin-Momentum Helical Locking in Bi2Se3 and Bi2Te3, demonstration of Topological-Order at 300K and a realization of topological-transport-regime
