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https://www.readbyqxmd.com/read/28719573/crystalline-metamaterials-for-topological-properties-at-subwavelength-scales
#1
Simon Yves, Romain Fleury, Thomas Berthelot, Mathias Fink, Fabrice Lemoult, Geoffroy Lerosey
The exciting discovery of topological condensed matter systems has lately triggered a search for their photonic analogues, motivated by the possibility of robust backscattering-immune light transport. However, topological photonic phases have so far only been observed in photonic crystals and waveguide arrays, which are inherently physically wavelength scaled, hindering their application in compact subwavelength systems. In this letter, we tackle this problem by patterning the deep subwavelength resonant elements of metamaterials onto specific lattices, and create crystalline metamaterials that can develop complex nonlocal properties due to multiple scattering, despite their very subwavelength spatial scale that usually implies to disregard their structure...
July 18, 2017: Nature Communications
https://www.readbyqxmd.com/read/28707934/topological-quantum-liquids-with-long-range-couplings
#2
Kristian Patrick, Titus Neupert, Jiannis K Pachos
Very few topological systems with long-range couplings have been considered so far due to our lack of analytic approaches. Here we extend the Kitaev chain, a 1D quantum liquid, to infinite-range couplings and study its topological properties. We demonstrate that, even though topological phases are intimately linked to the notion of locality, the infinite-range couplings give rise to topological zero and nonzero energy Majorana end modes depending on the boundary conditions of the system. We show that the analytically derived properties are to a large degree stable against modifications to decaying long-range couplings...
June 30, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28684520/quantized-electric-multipole-insulators
#3
Wladimir A Benalcazar, B Andrei Bernevig, Taylor L Hughes
The Berry phase provides a modern formulation of electric polarization in crystals. We extend this concept to higher electric multipole moments and determine the necessary conditions and minimal models for which the quadrupole and octupole moments are topologically quantized electromagnetic observables. Such systems exhibit gapped boundaries that are themselves lower-dimensional topological phases. Furthermore, they host topologically protected corner states carrying fractional charge, exhibiting fractionalization at the boundary of the boundary...
July 7, 2017: Science
https://www.readbyqxmd.com/read/28667305/complete-theory-of-symmetry-based-indicators-of-band-topology
#4
Hoi Chun Po, Ashvin Vishwanath, Haruki Watanabe
The interplay between symmetry and topology leads to a rich variety of electronic topological phases, protecting states such as the topological insulators and Dirac semimetals. Previous results, like the Fu-Kane parity criterion for inversion-symmetric topological insulators, demonstrate that symmetry labels can sometimes unambiguously indicate underlying band topology. Here we develop a systematic approach to expose all such symmetry-based indicators of band topology in all the 230 space groups. This is achieved by first developing an efficient way to represent band structures in terms of elementary basis states, and then isolating the topological ones by removing the subset of atomic insulators, defined by the existence of localized symmetric Wannier functions...
June 30, 2017: Nature Communications
https://www.readbyqxmd.com/read/28644652/topological-insulators-in-amorphous-systems
#5
Adhip Agarwala, Vijay B Shenoy
Much of the current understanding of topological insulators, which informs the experimental search for topological materials and systems, is based on crystalline band theory, where local electronic degrees of freedom at different crystal sites hybridize with each other in ways that produce nontrivial topology. Here we provide a novel theoretical demonstration of realizing topological phases in amorphous systems, as exemplified by a set of sites randomly located in space. We show this by constructing hopping models on such random lattices whose gapped ground states are shown to possess nontrivial topological nature (characterized by Bott indices) that manifests as quantized conductances in systems with a boundary...
June 9, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28632141/phase-transitions-of-the-dimerized-kane-mele-model-with-without-the-strong-interaction
#6
Tao Du, Yue-Xun Li, Yan Li, He-Lin Lu, Hui Zhang
The dimerized Kane-Mele model with/without the strong interaction is studied using analytical methods. The boundary of the topological phase transition of the model without strong interaction is obtained. Our results show that the occurrence of the transition only depends on dimerized parameter α . From the one-particle spectrum, we obtain the completed phase diagram including the quantum spin Hall (QSH) state and the topologically trivial insulator. Then, using different mean-field methods, we investigate the Mott transition and the magnetic transition of the strongly correlated dimerized Kane-Mele model...
June 20, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28617584/tunability-of-the-quantum-spin-hall-effect-in-bi-110-films-effects-of-electric-field-and-strain-engineering
#7
Sheng-Shi Li, Wei-Xiao Ji, Ping Li, Shu-Jun Hu, Li Cai, Chang-Wen Zhang, Shi-Shen Yan
The quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices due to their robust gapless edge states inside insulating bulk gap. However, the currently discussed QSH insulators usually suffer from ultrahigh vacuum or low temperature due to the small bulk gap, which limits their practical applications. Searching for large-gap QSH insulators is highly desirable. Here, the tunable QSH state of a Bi(110) films with a black phosphorus (BP) structure, which is robust against structural deformation and electric field, is explored by first-principles calculations...
June 15, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28615662/engineering-of-many-body-majorana-states-in-a-topological-insulator-s-wave-superconductor-heterostructure
#8
Hsiang-Hsuan Hung, Jiansheng Wu, Kuei Sun, Ching-Kai Chiu
We study a vortex chain in a thin film of a topological insulator with proximity-induced superconductivity-a promising platform to realize Majorana zero modes (MZMs)-by modeling it as a two-leg Majorana ladder. While each pair of MZMs hybridizes through vortex tunneling, we hereby show that MZMs can be stabilized on the ends of the ladder with the presence of tilted external magnetic field and four-Majorana interaction. Furthermore, a fruitful phase diagram is obtained by controlling the direction of magnetic field and the thickness of the sample...
June 14, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28600553/topological-phase-transition-in-single-crystals-of-cd1-xznx-3as2
#9
Hong Lu, Xiao Zhang, Yi Bian, Shuang Jia
Single crystals of (Cd1-xZnx)3As2 were synthesized from high-temperature solutions and characterized in terms of their structural and electrical properties. Based on the measurements of resistivity and Hall signals, we revealed a chemical-doping-controlled transition from a three-dimensional Dirac semimetal to a semiconductor with a critical point xc ~ 0.38. We observed structural transitions from a body-center tetragonal phase to a primitive tetragonal phase then back to a body-center tetragonal phase in the solid solutions as well, which are irrelevant to the topological phase transition...
June 9, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28598676/spectral-flow-and-global-topology-of-the-hofstadter-butterfly
#10
János K Asbóth, Andrea Alberti
We study the relation between the global topology of the Hofstadter butterfly of a multiband insulator and the topological invariants of the underlying Hamiltonian. The global topology of the butterfly, i.e., the displacement of the energy gaps as the magnetic field is varied by one flux quantum, is determined by the spectral flow of energy eigenstates crossing gaps as the field is tuned. We find that for each gap this spectral flow is equal to the topological invariant of the gap, i.e., the net number of edge modes traversing the gap...
May 26, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28598670/quantum-loop-topography-for-machine-learning
#11
Yi Zhang, Eun-Ah Kim
Despite rapidly growing interest in harnessing machine learning in the study of quantum many-body systems, training neural networks to identify quantum phases is a nontrivial challenge. The key challenge is in efficiently extracting essential information from the many-body Hamiltonian or wave function and turning the information into an image that can be fed into a neural network. When targeting topological phases, this task becomes particularly challenging as topological phases are defined in terms of nonlocal properties...
May 26, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28598638/many-body-topological-invariants-for-fermionic-symmetry-protected-topological-phases
#12
Hassan Shapourian, Ken Shiozaki, Shinsei Ryu
We define and compute many-body topological invariants of interacting fermionic symmetry-protected topological phases, protected by an orientation-reversing symmetry, such as time-reversal or reflection symmetry. The topological invariants are given by partition functions obtained by a path integral on unoriented spacetime which, as we show, can be computed for a given ground state wave function by considering a nonlocal operation, "partial" reflection or transpose. As an application of our scheme, we study the Z_{8} and Z_{16} classification of topological superconductors in one and three dimensions...
May 26, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28593950/origin-of-the-crossover-from-polarons-to-fermi-liquids-in-transition-metal-oxides
#13
Carla Verdi, Fabio Caruso, Feliciano Giustino
Transition metal oxides host a wealth of exotic phenomena ranging from charge, orbital and magnetic order to nontrivial topological phases and superconductivity. In order to translate these unique materials properties into device functionalities these materials must be doped; however, the nature of carriers and their conduction mechanism at the atomic scale remain unclear. Recent angle-resolved photoelectron spectroscopy investigations provided insight into these questions, revealing that the carriers of prototypical metal oxides undergo a transition from a polaronic liquid to a Fermi liquid regime with increasing doping...
June 8, 2017: Nature Communications
https://www.readbyqxmd.com/read/28584249/quantum-phase-transition-and-entanglement-in-topological-quantum-wires
#14
Jaeyoon Cho, Kun Woo Kim
We investigate the quantum phase transition of the Su-Schrieffer-Heeger (SSH) model by inspecting the two-site entanglements in the ground state. It is shown that the topological phase transition of the SSH model is signified by a nonanalyticity of local entanglement, which becomes discontinuous for finite even system sizes, and that this nonanalyticity has a topological origin. Such a peculiar singularity has a universal nature in one-dimensional topological phase transitions of noninteracting fermions. We make this clearer by pointing out that an analogous quantity in the Kitaev chain exhibiting the identical nonanalyticity is the local electron density...
June 5, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28580975/morphological-imperfections-of-epitaxial-graphene-from-a-hindrance-to-the-generation-of-new-photo-responses-in-the-visible-domain
#15
A Ben Gouider Trabelsi, F V Kusmartsev, M B Gaifullin, D M Forrester, A Kusmartseva, M Oueslati
We report the discovery of remarkable photo-physical phenomena with characteristics unique to epitaxial graphene grown on 6H-SiC (000-1). Surprisingly, the electrical resistance of graphene increases under light illumination in contrast to conventional materials where it normally decreases. The resistance shows logarithmic temperature dependences which may be attributed to an Altshuler-Aronov effect. We show that the photoresistance depends on the frequency of the irradiating light, with three lasers (red, green, and violet) used to demonstrate the phenomenon...
June 5, 2017: Nanoscale
https://www.readbyqxmd.com/read/28580929/three-dimensional-pentagon-carbon-with-a-genesis-of-emergent-fermions
#16
Chengyong Zhong, Yuanping Chen, Zhi-Ming Yu, Yuee Xie, Han Wang, Shengyuan A Yang, Shengbai Zhang
Carbon, the basic building block of our universe, enjoys a vast number of allotropic structures. Owing to its bonding characteristic, most carbon allotropes possess the motif of hexagonal rings. Here, with first-principles calculations, we discover a new metastable three-dimensional carbon allotrope entirely composed of pentagon rings. The unique structure of this Pentagon Carbon leads to extraordinary electronic properties, making it a cornucopia of emergent topological fermions. Under lattice strain, Pentagon Carbon exhibits topological phase transitions, generating a series of novel quasiparticles, from isospin-1 triplet fermions to triply degenerate fermions and further to Hopf-link Weyl-loop fermions...
June 5, 2017: Nature Communications
https://www.readbyqxmd.com/read/28580420/a-pressure-induced-topological-phase-with-large-berry-curvature-in-pb1-x-sn-x-te
#17
Tian Liang, Satya Kushwaha, Jinwoong Kim, Quinn Gibson, Jingjing Lin, Nicholas Kioussis, Robert J Cava, N Phuan Ong
The picture of how a gap closes in a semiconductor has been radically transformed by topological concepts. Instead of the gap closing and immediately reopening, topological arguments predict that, in the absence of inversion symmetry, a metallic phase protected by Weyl nodes persists over a finite interval of the tuning parameter (for example, pressure P). The gap reappears when the Weyl nodes mutually annihilate. We report evidence that Pb1-x Sn x Te exhibits this topological metallic phase. Using pressure to tune the gap, we have tracked the nucleation of a Fermi surface droplet that rapidly grows in volume with P...
May 2017: Science Advances
https://www.readbyqxmd.com/read/28541248/switch-effect-of-the-nonquantized-intrinsic-spin-hall-conductivity-in-monolayered-monoclinic-transition-metal-dichalcogenides
#18
Xianqing Lin, Jun Ni
First-principles calculations have been performed to study the intrinsic spin Hall effect (SHE) and its behavior under vertical electric field in monoclinic transition metal dichalcogenide monolayers (1T'-MX2 with M  =  Mo, W and X  =  S, Se, Te). We find that the pristine systems exhibit nonquantized intrinsic spin Hall conductivity (SHC) due to the unconserved spin around the direct band gaps though they have nontrivial band topology. The unconserved spin is attributed to the band crossings at Fermi levels for systems without spin-orbit coupling and the distinct composition of the band states around the crossings...
May 25, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28537276/magnetic-field-induced-multiple-topological-phases-in-pyrochlore-iridates-with-mott-criticality
#19
Kentaro Ueda, Taekoo Oh, Bohm-Jung Yang, Ryoma Kaneko, Jun Fujioka, Naoto Nagaosa, Yoshinori Tokura
The interplay between electron correlation and spin-orbit coupling in solids has been proven to be an abundant gold mine for emergent topological phases. Here we report the results of systematic magnetotransport study on bandwidth-controlled pyrochlore iridates R2Ir2O7 near quantum metal-insulator transition (MIT). The application of a magnetic field along [001] crystallographic direction (H//[001]) significantly decreases resistivity while producing a unique Hall response, which indicates the emergence of the novel semi-metallic state in the course of the magnetic transformation from all-in all-out (AIAO, 4/0) to 2-in 2-out (2/2) spin configuration...
May 24, 2017: Nature Communications
https://www.readbyqxmd.com/read/28534501/electronic-evidence-of-temperature-induced-lifshitz-transition-and-topological-nature-in-zrte5
#20
Yan Zhang, Chenlu Wang, Li Yu, Guodong Liu, Aiji Liang, Jianwei Huang, Simin Nie, Xuan Sun, Yuxiao Zhang, Bing Shen, Jing Liu, Hongming Weng, Lingxiao Zhao, Genfu Chen, Xiaowen Jia, Cheng Hu, Ying Ding, Wenjuan Zhao, Qiang Gao, Cong Li, Shaolong He, Lin Zhao, Fengfeng Zhang, Shenjin Zhang, Feng Yang, Zhimin Wang, Qinjun Peng, Xi Dai, Zhong Fang, Zuyan Xu, Chuangtian Chen, X J Zhou
The topological materials have attracted much attention for their unique electronic structure and peculiar physical properties. ZrTe5 has host a long-standing puzzle on its anomalous transport properties manifested by its unusual resistivity peak and the reversal of the charge carrier type. It is also predicted that single-layer ZrTe5 is a two-dimensional topological insulator and there is possibly a topological phase transition in bulk ZrTe5. Here we report high-resolution laser-based angle-resolved photoemission measurements on the electronic structure and its detailed temperature evolution of ZrTe5...
May 23, 2017: Nature Communications
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