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"topological phase"

Furu Zhang, Jianhui Zhou, Di Xiao, Yugui Yao
Band inversion has led to rich physical effects in both topological insulators and topological semimetals. It has been found that the inverted band structure with the Mexican-hat dispersion could enhance the interband correlation leading to a strong intrinsic plasmon excitation. Its frequency ranges from several meV to tens of meV and can be effectively tuned by the external fields. The electron-hole asymmetric term splits the peak of the plasmon excitation into double peaks. The fate and properties of this plasmon excitation can also act as a probe to characterize the topological phases even in lightly doped systems...
December 29, 2017: Physical Review Letters
Ce Shang, Xianfeng Chen, Weidong Luo, Fangwei Ye
We consider the topological characteristics of the spin-orbital coupling particles loaded in one-dimensional (1D) optical superlattices subject to the Zeeman field. The phase shift of the superlattice provides a virtual dimension which allows us to simulate two-dimensional topological phases with a physically 1D system. The system possesses a variety of quantum phase transitions over a large parametric space and two important topological phases, namely, quantum anomalous Hall (QAH) and quantum spin Hall (QSH) phases are found to coexist in the system, but they reside in different bandgaps...
January 15, 2018: Optics Letters
Rokyeon Kim, Jaejun Yu, Hosub Jin
Topological electronics is a new field that uses topological charges as current-carrying degrees of freedom. For topological electronics applications, systems should host topologically distinct phases to control the topological domain boundary through which the topological charges can flow. Due to their multiple Dirac cones and the π-Berry phase of each Dirac cone, graphene-like electronic structures constitute an ideal platform for topological electronics; graphene can provide various topological phases when incorporated with large spin-orbit coupling and mass-gap tunability via symmetry-breaking...
January 11, 2018: Scientific Reports
Gábor B Halász, Timothy H Hsieh, Leon Balents
We provide a new perspective on fracton topological phases, a class of three-dimensional topologically ordered phases with unconventional fractionalized excitations that are either completely immobile or only mobile along particular lines or planes. We demonstrate that a wide range of these fracton phases can be constructed by strongly coupling mutually intersecting spin chains and explain via a concrete example how such a coupled-spin-chain construction illuminates the generic properties of a fracton phase...
December 22, 2017: Physical Review Letters
Sanfeng Wu, Valla Fatemi, Quinn D Gibson, Kenji Watanabe, Takashi Taniguchi, Robert J Cava, Pablo Jarillo-Herrero
A variety of monolayer crystals have been proposed to be two-dimensional topological insulators exhibiting the quantum spin Hall effect (QSHE), possibly even at high temperatures. Here we report the observation of the QSHE in monolayer tungsten ditelluride (WTe2) at temperatures up to 100 kelvin. In the short-edge limit, the monolayer exhibits the hallmark transport conductance, ~e2/h per edge, where e is the electron charge and h is Planck's constant. Moreover, a magnetic field suppresses the conductance, and the observed Zeeman-type gap indicates the existence of a Kramers degenerate point and the importance of time-reversal symmetry for protection from elastic backscattering...
January 5, 2018: Science
Michael Lohse, Christian Schweizer, Hannah M Price, Oded Zilberberg, Immanuel Bloch
The discovery of topological states of matter has greatly improved our understanding of phase transitions in physical systems. Instead of being described by local order parameters, topological phases are described by global topological invariants and are therefore robust against perturbations. A prominent example is the two-dimensional (2D) integer quantum Hall effect: it is characterized by the first Chern number, which manifests in the quantized Hall response that is induced by an external electric field...
January 3, 2018: Nature
Matthias Saba, Joachim M Hamm, Jeremy J Baumberg, Ortwin Hess
Topological phases derived from point degeneracies in photonic band structures show intriguing and unique behavior. Previously identified band degeneracies are based on accidental degeneracies and subject to engineering on a case-by-case basis. Here we show that deterministic pseudo Weyl points with nontrivial topology and hyperconic dispersion exist at the Brillouin zone center of chiral cubic symmetries. This conceivably allows realization of topologically protected frequency isolated surface bands in 3D and n=0 properties as demonstrated for a nanoplasmonic system and a photonic crystal...
December 1, 2017: Physical Review Letters
Areg Ghazaryan, Tobias Graß, Michael J Gullans, Pouyan Ghaemi, Mohammad Hafezi
We show how to realize two-component fractional quantum Hall phases in monolayer graphene by optically driving the system. A laser is tuned into resonance between two Landau levels, giving rise to an effective tunneling between these two synthetic layers. Remarkably, because of this coupling, the interlayer interaction at nonzero relative angular momentum can become dominant, resembling a hollow-core pseudopotential. In the weak tunneling regime, this interaction favors the formation of singlet states, as we explicitly show by numerical diagonalization, at fillings ν=1/2 and ν=2/3...
December 15, 2017: Physical Review Letters
Jayita Nayak, Nitesh Kumar, Shu-Chun Wu, Chandra Shekhar, Jorg Fink, Emile D L Rienks, Gerhard Fecher, Yan Sun, Claudia Felser
The topological phases of matter provide the opportunity to observe many exotic properties, such as the existence of two-dimensional topological surface states in the form of Dirac cones in topological insulators and chiral transport through the open Fermi arc in Weyl semimetals. However, these properties affect the transport characteristics and, therefore, may be useful for applications only if the topological phenomena occur near the Fermi level. CaAgAs is a promising candidate for which the ab-initio calculations predict line-nodes at the Fermi energy...
December 14, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Gerbold C Ménard, Sébastien Guissart, Christophe Brun, Raphaël T Leriche, Mircea Trif, François Debontridder, Dominique Demaille, Dimitri Roditchev, Pascal Simon, Tristan Cren
Just like insulators can present topological phases characterized by Dirac edge states, superconductors can exhibit topological phases characterized by Majorana edge states. In particular, one-dimensional topological superconductors are predicted to host zero-energy Majorana fermions at their extremities. By contrast, two-dimensional superconductors have a one-dimensional boundary which would naturally lead to propagating Majorana edge states characterized by a Dirac-like dispersion. In this paper we present evidences of one-dimensional dispersive in-gap edge states surrounding a two-dimensional topological superconducting domain consisting of a monolayer of Pb covering magnetic Co-Si islands grown on Si(111)...
December 11, 2017: Nature Communications
Xiaofan Zhou, Jian-Song Pan, Zheng-Xin Liu, Wei Zhang, Wei Yi, Gang Chen, Suotang Jia
We discuss the quantum simulation of symmetry-protected topological (SPT) states for interacting fermions in quasi-one-dimensional gases of alkaline-earth-like atoms such as ^{173}Yb. Taking advantage of the separation of orbital and nuclear-spin degrees of freedom in these atoms, we consider Raman-assisted spin-orbit couplings in the clock states, which, together with the spin-exchange interactions in the clock-state manifolds, give rise to SPT states for interacting fermions. We numerically investigate the phase diagram of the system, and study the phase transitions between the SPT phase and the symmetry-breaking phases...
November 3, 2017: Physical Review Letters
Soonwon Choi, Norman Y Yao, Mikhail D Lukin
We propose and analyze a method to engineer effective interactions in an ensemble of d-level systems (qudits) driven by global control fields. In particular, we present (i) a necessary and sufficient condition under which a given interaction can be decoupled, (ii) the existence of a universal sequence that decouples any (cancelable) interaction, and (iii) an efficient algorithm to engineer a target Hamiltonian from an initial Hamiltonian (if possible). We illustrate the potential of this method with two examples...
November 3, 2017: Physical Review Letters
Ananda Roy, Barbara M Terhal, Fabian Hassler
The toric code based on Majorana fermions on mesoscopic superconducting islands is a promising candidate for quantum information processing. In the limit of vanishing Cooper-pair tunneling, it has been argued that the phase transition separating the topologically ordered phase of the toric code from the trivial one is in the universality class of the (2+1)D XY model. On the other hand, in the limit of infinitely large Cooper-pair tunneling, the phase transition is in the universality class of the (2+1)D Ising model...
November 3, 2017: Physical Review Letters
Yuxuan Wang, Liang Fu
We study the phase transition between a trivial and a time-reversal-invariant topological superconductor in a single-band system. By analyzing the interplay of symmetry, topology, and energetics, we show that for a generic normal state band structure, the phase transition occurs via extended intermediate phases in which even- and odd-parity pairing components coexist. For inversion-symmetric systems, the coexistence phase spontaneously breaks time-reversal symmetry. For noncentrosymmetric superconductors, the low-temperature intermediate phase is time-reversal breaking, while the high-temperature phase preserves time-reversal symmetry and has topologically protected line nodes...
November 3, 2017: Physical Review Letters
Wei-Wei Zhang, Barry C Sanders, Simon Apers, Sandeep K Goyal, David L Feder
We show that the evolution of two-component particles governed by a two-dimensional spin-orbit lattice Hamiltonian can reveal transitions between topological phases. A kink in the mean width of the particle distribution signals the closing of the band gap, a prerequisite for a quantum phase transition between topological phases. Furthermore, for realistic and experimentally motivated Hamiltonians, the density profile in topologically nontrivial phases displays characteristic rings in the vicinity of the origin that are absent in trivial phases...
November 10, 2017: Physical Review Letters
Iris Cong, Meng Cheng, Zhenghan Wang
This Letter discusses topological quantum computation with gapped boundaries of two-dimensional topological phases. Systematic methods are presented to encode quantum information topologically using gapped boundaries, and to perform topologically protected operations on this encoding. In particular, we introduce a new and general computational primitive of topological charge measurement and present a symmetry-protected implementation of this primitive. Throughout the Letter, a concrete physical example, the Z_{3} toric code [D(Z_{3})], is discussed...
October 27, 2017: Physical Review Letters
Qinghua Guo, Biao Yang, Lingbo Xia, Wenlong Gao, Hongchao Liu, Jing Chen, Yuanjiang Xiang, Shuang Zhang
Topological semimetals, representing a new topological phase that lacks a full band gap in bulk states and exhibiting nontrivial topological orders, recently have been extended to photonic systems, predominantly in photonic crystals and to a lesser extent metamaterials. Photonic crystal realizations of Dirac degeneracies are protected by various space symmetries, where Bloch modes span the spin and orbital subspaces. Here, we theoretically show that Dirac points can also be realized in effective media through the intrinsic degrees of freedom in electromagnetism under electromagnetic duality...
November 24, 2017: Physical Review Letters
Pedro Nevado, Samuel Fernández-Lorenzo, Diego Porras
Topological insulating phases are primarily associated with condensed-matter systems, which typically feature short-range interactions. Nevertheless, many realizations of quantum matter can exhibit long-range interactions, and it is still largely unknown the effect that these latter may exert upon the topological phases. In this Letter, we investigate the Su-Schrieffer-Heeger topological insulator in the presence of long-range interactions. We show that this model can be readily realized in quantum simulators with trapped ions by means of a periodic driving...
November 24, 2017: Physical Review Letters
Dongchao Wang, Li Chen, Hongmei Liu, Changmin Shi, Xiaoli Wang, Guangliang Cui, Pinhua Zhang, Yeqing Chen
The researches for new quantum spin Hall (QSH) insulators with large bulk energy gap are of much significance for their practical applications at room temperature in electronic devices with low-energy consumption. By means of first-principles calculations, we proposed that methyl-decorated stanene (SnCH3) film can be tuned into QSH insulator under critical tensile strain of 6%. The nonzero topological invariant and helical edge states further confirm the nontrivial nature in stretched SnCH3 film. The topological phase transition originates from the s-p xy type band inversion at the Γ point with the strain increased...
December 6, 2017: Scientific Reports
Dusan Jakovljevic, Marko Grujic, Milan Tadic, Francois M Peeters
Due to nonzero intrinsic spin-orbit interaction in buckled honeycomb crystal structures, silicene and germanene exhibit interesting topological properties, and are therefore candidates for the realization of the quantum spin Hall effect. We employ the Kane-Mele model to investigate the electron states in hexagonal silicene and germanene nanorings having either zigzag or armchair edges in the presence of a perpendicular magnetic field. We present results for the energy spectra as function of magnetic field, the electron density of the spin-up and spin-down states in the ring plane, and the calculation of the probability current density...
November 30, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
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