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"topological phase"

Wei-Wei Yang, Lei Li, Jing-Sheng Zhao, Xiao-Xiong Liu, Jian-Bo Deng, Xianru Hu
By doing calculations based on density functional theory (DFT), we predict that the two-dimensional anti-ferromagnetic (AFM) NiOsCl$_6$ as a Chern insulator can realize the quantum anomalous Hall (QAH) effect. We investigate the magnetocrystalline anisotropy (MAC) energies in different magnetic configurations and the N\'{e}el AFM configuration is proved to be ground state. When considering spin-orbit coupling (SOC), this layered material with spins perpendicular to the plane shows properties as a Chern insulator characterized by an inversion band structure and a nonzero Chern number...
March 19, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Kenta Kuroda, M Ochi, H S Suzuki, M Hirayama, M Nakayama, R Noguchi, C Bareille, S Akebi, S Kunisada, T Muro, M D Watson, H Kitazawa, Y Haga, T K Kim, M Hoesch, S Shin, R Arita, Takeshi Kondo
Experimental determinations of bulk band topology in the solid states have been so far restricted to only indirect investigation through the probing of surface states predicted by electronic structure calculations. We here present an alternative approach to determine the band topology by means of bulk-sensitive soft x-ray angle-resolved photoemission spectroscopy. We investigate the bulk electronic structures of the series materials, Ce monopnictides (CeP, CeAs, CeSb, and CeBi). By performing a paradigmatic study of the band structures as a function of their spin-orbit coupling, we draw the topological phase diagram and unambiguously reveal the topological phase transition from a trivial to a nontrivial regime in going from CeP to CeBi induced by the band inversion...
February 23, 2018: Physical Review Letters
A M Kadykov, S S Krishtopenko, B Jouault, W Desrat, W Knap, S Ruffenach, C Consejo, J Torres, S V Morozov, N N Mikhailov, S A Dvoretskii, F Teppe
We report a direct observation of temperature-induced topological phase transition between the trivial and topological insulator states in an HgTe quantum well. By using a gated Hall bar device, we measure and represent Landau levels in fan charts at different temperatures, and we follow the temperature evolution of a peculiar pair of "zero-mode" Landau levels, which split from the edge of electronlike and holelike subbands. Their crossing at a critical magnetic field B_{c} is a characteristic of inverted band structure in the quantum well...
February 23, 2018: Physical Review Letters
E Colomés, M Franz
Topological phases of fermions in two dimensions are often characterized by chiral edge states. By definition, these propagate in opposite directions at the two parallel edges when the sample geometry is that of a rectangular strip. We introduce here a model which exhibits what we call "antichiral" edge modes. These propagate in the same direction at both parallel edges of the strip and are compensated by counterpropagating modes that reside in the bulk. General arguments and numerical simulations show that backscattering is suppressed even when strong disorder is present in the system...
February 23, 2018: Physical Review Letters
Christopher W Peterson, Wladimir A Benalcazar, Taylor L Hughes, Gaurav Bahl
The theory of electric polarization in crystals defines the dipole moment of an insulator in terms of a Berry phase (geometric phase) associated with its electronic ground state. This concept not only solves the long-standing puzzle of how to calculate dipole moments in crystals, but also explains topological band structures in insulators and superconductors, including the quantum anomalous Hall insulator and the quantum spin Hall insulator, as well as quantized adiabatic pumping processes. A recent theoretical study has extended the Berry phase framework to also account for higher electric multipole moments, revealing the existence of higher-order topological phases that have not previously been observed...
March 14, 2018: Nature
S A Owerre
Topological magnon insulators are the bosonic analogs of electronic topological insulators. They are manifested in magnetic materials with topologically nontrivial magnon bands as realized experimentally in a quasi-two-dimensional (quasi-2D) kagomé ferromagnet Cu(1-3, bdc), and they also possess protected magnon edge modes. These topological magnetic materials can transport heat as well as spin currents, hence they can be useful for spintronic applications. Moreover, as magnons are charge-neutral spin-1 bosonic quasiparticles with a magnetic dipole moment, topological magnon materials can also interact with electromagnetic fields through the Aharonov-Casher effect...
March 13, 2018: Scientific Reports
Satyendra Nath Gupta, Anjali Singh, Koushik Pal, D Victor S Muthu, Chandra Shekhar, Moaz A ElGhazali, Pavel Naumov, Sergey Medvedev, Claudia Felser, Umesh V Waghmare, A K Sooda
High pressure Raman, resistivity and synchrotron x-ray diffraction studies on Weyl semimetals NbAs and TaAs have been carried out along with density functional theoretical (DFT) analysis to explain pressure-induced structural and electronic topological phase transitions. The frequencies of first order Raman modes harden with increasing pressure, exhibiting a slope change at P<sub>c</sub><sup>Nb</sup> ~15 GPa for NbAs and P<sub>c</sub><sup>Ta</sup> ~16 GPa for TaAs...
March 12, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Wenlong Gao, Biao Yang, Ben Tremain, Hongchao Liu, Qinghua Guo, Lingbo Xia, Alastair P Hibbins, Shuang Zhang
Nodal line semimetals (NLS) are three-dimensional (3D) crystals that support band crossings in the form of one-dimensional rings in the Brillouin zone. In the presence of spin-orbit coupling or lowered crystal symmetry, NLS may transform into Dirac semimetals, Weyl semimetals, or 3D topological insulators. In the photonics context, despite the realization of topological phases, such as Chern insulators, topological insulators, Weyl, and Dirac degeneracies, no experimental demonstration of photonic nodal lines (NLs) has been reported so far...
March 5, 2018: Nature Communications
Maxim A Gorlach, Xiang Ni, Daria A Smirnova, Dmitry Korobkin, Dmitry Zhirihin, Alexey P Slobozhanyuk, Pavel A Belov, Andrea Alù, Alexander B Khanikaev
Topological phase transitions in condensed matter systems give rise to exotic states of matter such as topological insulators, superconductors, and superfluids. Photonic topological systems open a whole new realm of research and technological opportunities, exhibiting a number of important distinctions from their condensed matter counterparts. Photonic modes can leak into free space, which makes it possible to probe topological photonic phases by spectroscopic means via Fano resonances. Based on this idea, we develop a technique to retrieve the topological properties of all-dielectric metasurfaces from the measured far-field scattering characteristics...
March 2, 2018: Nature Communications
Leslie M Schoop, Andreas Topp, Judith Lippmann, Fabio Orlandi, Lukas Müchler, Maia G Vergniory, Yan Sun, Andreas W Rost, Viola Duppel, Maxim Krivenkov, Shweta Sheoran, Pascal Manuel, Andrei Varykhalov, Binghai Yan, Reinhard K Kremer, Christian R Ast, Bettina V Lotsch
Recent interest in topological semimetals has led to the proposal of many new topological phases that can be realized in real materials. Next to Dirac and Weyl systems, these include more exotic phases based on manifold band degeneracies in the bulk electronic structure. The exotic states in topological semimetals are usually protected by some sort of crystal symmetry, and the introduction of magnetic order can influence these states by breaking time-reversal symmetry. We show that we can realize a rich variety of different topological semimetal states in a single material, CeSbTe...
February 2018: Science Advances
Marta Brzezińska, Maciej Bieniek, Tomasz Woźniak, Paweł Potasz, Arkadiusz Wójs
We study topological properties of Bi1-x Sbx bilayers in the (1 1 1) plane using entanglement measures. Electronic structures are investigated within multi-orbital tight-binding model and structural stability is confirmed through first-principles calculations. The topologically non-trivial nature of the bismuth bilayer is proved by the presence of spectral flow in the entanglement spectrum. We consider topological phase transitions driven by a composition change x, an applied external electric field in Bi bilayers and strain in Sb bilayers...
February 28, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Pengfei Zhang, Huitao Shen, Hui Zhai
In this Letter we supervisedly train neural networks to distinguish different topological phases in the context of topological band insulators. After training with Hamiltonians of one-dimensional insulators with chiral symmetry, the neural network can predict their topological winding numbers with nearly 100% accuracy, even for Hamiltonians with larger winding numbers that are not included in the training data. These results show a remarkable success that the neural network can capture the global and nonlinear topological features of quantum phases from local inputs...
February 9, 2018: Physical Review Letters
Ruben Verresen, Nick G Jones, Frank Pollmann
We show that topology can protect exponentially localized, zero energy edge modes at critical points between one-dimensional symmetry-protected topological phases. This is possible even without gapped degrees of freedom in the bulk-in contrast to recent work on edge modes in gapless chains. We present an intuitive picture for the existence of these edge modes in the case of noninteracting spinless fermions with time-reversal symmetry (BDI class of the tenfold way). The stability of this phenomenon relies on a topological invariant defined in terms of a complex function, counting its zeros and poles inside the unit circle...
February 2, 2018: Physical Review Letters
Di Xiao, Jue Jiang, Jae-Ho Shin, Wenbo Wang, Fei Wang, Yi-Fan Zhao, Chaoxing Liu, Weida Wu, Moses H W Chan, Nitin Samarth, Cui-Zu Chang
The "magnetoelectric effect" arises from the coupling between magnetic and electric properties in materials. The Z_{2} invariant of topological insulators (TIs) leads to a quantized version of this phenomenon, known as the topological magnetoelectric (TME) effect. This effect can be realized in a new topological phase called an "axion insulator" whose surface states are all gapped but the interior still obeys time reversal symmetry. We demonstrate such a phase using electrical transport measurements in a quantum anomalous Hall (QAH) sandwich heterostructure, in which two compositionally different magnetic TI layers are separated by an undoped TI layer...
February 2, 2018: Physical Review Letters
Shaoyong Huo, Jiu-Jiu Chen, Hongbo Huang
Topological phononic insulators (TPnIs) have promising application in manipulation of acoustic waves for design of the low-loss transmission and perfectly integrated communication devices. Since solid phononic crystals exists as a transverse polarization mode and a mixed longitudinal-transverse polarization mode, the realization of topological edge states for both out-of-plane and in-plane bulk elastic waves are desirable to enhance the controllability of the edge waves in solid system. In this paper, a two-dimensional (2D) solid/solid hexagonal-latticed phononic system that simultaneously supports the fascinating topologically protected edge states for out-of-plane and in-plane bulk elastic waves is investigated...
February 26, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
M A Griffith, M A Continentino
Topological phase transitions constitute a new class of quantum critical phenomena. They cannot be described within the usual framework of the Landau theory since, in general, the different phases cannot be distinguished by an order parameter, neither can they be related to different symmetries. In most cases, however, one can identify a diverging length at these topological transitions. This allows us to describe them using a scaling approach and to introduce a set of critical exponents that characterize their universality class...
January 2018: Physical Review. E
Jia-Bin You, Wanli Yang
The thermodynamic quantities which are related to energy-level statistics are used to characterize the real-space topology of the Rice-Mele model. Through studying the energy spectrum of the model under different boundary conditions, we found that the non-normalizable wave function for the infinite domain is reduced to the edge state adhered to the boundary. For the finite domain with symmetric boundary condition, the critical point for the topological phase transition is equal to the inverse of the domain length...
January 2018: Physical Review. E
Marta Brzezińska, Maciej Bieniek, Tomasz Woźniak, Paweł Potasz, Arkadiusz Wójs
We study topological properties of Bi$_{1-x}$Sb$_{x}$ bilayers in the (111) plane using entanglement measures. Electronic structures are investigated within multi-orbital tight-binding model and structural stability is confirmed through first-principles calculations. Topologically non-trivial nature of bismuth bilayer is proved by the presence of spectral flow in the entanglement spectrum. We consider topological phase transitions driven by a composition change x, an applied external electric field in Bi bilayer and strain in Sb bilayer...
February 14, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Mukesh Kumar Shukla, Ritwick Das
We present an investigation to ascertain the existence of Tamm-plasmon-polariton-like modes in one-dimensional (1D) quasi-periodic photonic systems. Photonic bandgap formation in quasi-crystals is essentially a consequence of long-range periodicity exhibited by multilayers and, thus, it can be explained using the dispersion relation in the Brillouin zone. Defining a "Zak"-like topological phase in 1D quasi-crystals, we propose a recipe to ascertain the existence of Tamm-like photonic surface modes in a metal-terminated quasi-crystal lattice...
February 1, 2018: Optics Letters
Xiaosen Yang, Beibing Huang, Zhengling Wang
We propose a simple approach to realize two-dimensional Floquet topological superfluid by periodically tuning the depth of square optical lattice potentials. We show that the periodic driving can induce topological phase transitions between trivial superfluid and Floquet topological superfluid. For this systems we verify the anomalous bulk-boundary correspondence, namely that the robust chiral Floquet edge states can appear even when the winding number of all the bulk Floquet bands is zero. We establish the existence of two Floquet Majorana zero modes separated in the quasienergy space, with ε0,π = 0,π/T at the topological defects...
February 2, 2018: Scientific Reports
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