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topological phases

Hao Huang, Xiaohui Ren, Zhongjun Li, Huide Wang, Zongyu Huang, Hui Qiao, Pinghua Tang, Jinlai Zhao, Weiyuan Liang, Yanqi Ge, Jie Liu, Jianqing Li, Xiang Qi, Han Zhang
Two dimensional (2D) Bi nano-sheets had been employed to fabricate electrodes for broadband photo-detection. A series of characterization techniques including SEM and HRTEM verify that Bi nanosheets with intact lamellar structure have been obtained after facile liquid phase exfoliation. In the meanwhile, UV-Vis and Raman spectra are also carried out and confirm the inherent optical and physical properties of Bi nanosheets. Inherited from the topological characteristics of Bi bulk counterpart, the resultant Bi nanosheet-based photo-detector exhibits preferable photo-response activity as well as environmental robustness...
March 15, 2018: Nanotechnology
Junjun Xu, Qiang Gu, Erich J Mueller
We analyze an experimentally realizable model of bosons in a zigzag optical lattice, showing that, by rapidly modulating the magnetic field, one can tune interaction parameters and realize an analog of the Haldane phase. We explain how quantum gas microscopy can be used to detect this phase's nonlocal string order and its topological edge states. We model the detection process. We also find that this model can display supersolid correlations, but argue that they only occur at parameter values which would be challenging to realize in an experiment...
February 23, 2018: Physical Review Letters
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
Keshav Shrestha, Vera Marinova, Bernd Lorenz, Paul C W Chu
We present a systematic quantum oscillations study on a metallic, <i>p</i>-type Bi<sub>2</sub>Te<sub>3</sub> topological single crystal in magnetic fields up to <i>B</i> = 7 T. The maxima/minima positions of oscillations measured at different tilt angles align to one another when plotted as a function of the normal component of magnetic field, confirming the presence of the 2D Fermi surface. Additionally, the Berry phase, β = 0...
March 15, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
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
Felix Büttner, Ivan Lemesh, Geoffrey S D Beach
Magnetic skyrmions are topological quasiparticles of great interest for data storage applications because of their small size, high stability, and ease of manipulation via electric current. However, although models exist for some limiting cases, there is no universal theory capable of accurately describing the structure and energetics of all skyrmions. The main barrier is the complexity of non-local stray field interactions, which are usually included through crude approximations. Here we present an accurate analytical framework to treat isolated skyrmions in any material, assuming only a circularly-symmetric 360° domain wall profile and a homogeneous magnetization profile in the out-of-plane direction...
March 13, 2018: Scientific Reports
Horacio Parraga, Francisco Javier Arranz, Rosa Maria Benito, Florentino Borondo
The dynamical characteristics of a region of regular vibrational motion in the sea of chaos above the saddle point corresponding to the linear C-N-K configuration is examined in detail. To explain the origin of this regularity, the associated phase space structures have been characterized using suitably defined Poincar\'e surfaces of section, identifying the different resonances between the stretching and bending modes, as a function of excitation energy. The corresponding topology is elucidated by means of periodic orbit analysis...
March 13, 2018: Journal of Physical Chemistry. A
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
Charles N Melton, Sheida T Riahinasab, Amir Keshavarz, Benjamin J Stokes, Linda S Hirst
When nanoparticle self-assembly takes place in an anisotropic liquid crystal environment, fascinating new effects can arise. The presence of elastic anisotropy and topological defects can direct spatial organization. An important goal in nanoscience is to direct the assembly of nanoparticles over large length scales to produce macroscopic composite materials; however, limitations on spatial ordering exist due to the inherent disorder of fluid-based methods. In this paper we demonstrate the formation of quantum dot clusters and spherical capsules suspended within spherical liquid crystal droplets as a method to position nanoparticle clusters at defined locations...
March 7, 2018: Nanomaterials
Lei Gao, Jia-Tao Sun, Jian-Chen Lu, Hang Li, Kai Qian, Shuai Zhang, Yu-Yang Zhang, Tian Qian, Hong Ding, Xiao Lin, Shixuan Du, Hong-Jun Gao
2D transition metal chalcogenides have attracted tremendous attention due to their novel properties and potential applications. Although 2D transition metal dichalcogenides are easily fabricated due to their layer-stacked bulk phase, 2D transition metal monochalcogenides are difficult to obtain. Recently, a single atomic layer transition metal monochalcogenide (CuSe) with an intrinsic pattern of nanoscale triangular holes is fabricated on Cu(111). The first-principles calculations show that free-standing monolayer CuSe with holes is not stable, while hole-free CuSe is endowed with the Dirac nodal line fermion (DNLF), protected by mirror reflection symmetry...
March 8, 2018: Advanced Materials
Bramaramba Gnapareddy, Sreekantha Reddy Dugasani, Junyoung Son, Sung Ha Park
DNA is considered as a useful building bio-material, and it serves as an efficient template to align functionalized nanomaterials. Riboflavin (RF)-doped synthetic double-crossover DNA (DX-DNA) lattices and natural salmon DNA (SDNA) thin films were constructed using substrate-assisted growth and drop-casting methods, respectively, and their topological, chemical and electro-optical characteristics were evaluated. The critical doping concentrations of RF ([RF]C , approx. 5 mM) at given concentrations of DX-DNA and SDNA were obtained by observing the phase transition (from crystalline to amorphous structures) of DX-DNA and precipitation of SDNA in solution above [RF]C ...
February 2018: Royal Society Open Science
Natalie Gaio, Alice Martino, Zacharie Toth, J Tracy Watson, Daemeon Nicolaou, Sarah McBride-Gagyi
The Masquelet technique is a surgical procedure to regenerate segmental bone defects. The two-phase treatment relies on the production of a vascularized foreign-body membrane to support bone grafts over three times larger than the traditional maximum. Historically, the procedure has always utilized a bone cement spacer to evoke membrane production. However, membrane formation can easily be effected by implant surface properties such as material and topology. This study sought to determine if the membrane's mechanical or barrier properties are affected by changing the spacer material to titanium or roughening the surface finish...
February 27, 2018: Journal of Biomechanics
Ceng-Ceng Ren, Shu-Feng Zhang, Wei-Xiao Ji, Chang-Wen Zhang, Ping Li, Pei-Ji Wang
Electronic and topological properties of two-dimensional germanene modified by functional group X (X = H, F, OH, CH₃) at full coverage are studied with first-principles calculation. Without considering the effect of spin-orbit coupling (SOC), all functionalized configurations become semiconductors, removing the Dirac cone at K point in pristine germanene. We also find that their band gaps can be especially well tuned by an external strain. When the SOC is switched on, GeX (X = H, CH₃) is a normal insulator and strain leads to a phase transition to a topological insulator (TI) phase...
March 6, 2018: Nanomaterials
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
Eric M Spanton, Alexander A Zibrov, Haoxin Zhou, Takashi Taniguchi, Kenji Watanabe, Michael P Zaletel, Andrea F Young
Topologically ordered phases are characterized by long-range quantum entanglement and fractional statistics rather than by symmetry breaking. First observed in a fractionally filled continuum Landau level, topological order has since been proposed to arise more generally at fractional fillings of topologically non-trivial "Chern" bands. Here, we report the observation of gapped states at fractional fillings of Harper-Hofstadter bands arising from the interplay of a magnetic field and a superlattice potential in a bilayer graphene/hexagonal boron nitride heterostructure...
March 1, 2018: Science
Marcello Merli, Alessandro Pavese
The critical points analysis of electron density, i.e. ρ(x), from ab initio calculations is used in combination with the catastrophe theory to show a correlation between ρ(x) topology and the appearance of instability that may lead to transformations of crystal structures, as a function of pressure/temperature. In particular, this study focuses on the evolution of coalescing non-degenerate critical points, i.e. such that ∇ρ(xc ) = 0 and λ1 , λ2 , λ3 ≠ 0 [λ being the eigenvalues of the Hessian of ρ(x) at xc ], towards degenerate critical points, i...
March 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
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