Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A18: Topological, Electronic and Photonic Properties of Nanostructures and Metamaterials |
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Sponsoring Units: DCMP Chair: Chih-Chun Chien, University of California, Merced Room: LACC 306B |
Monday, March 5, 2018 8:00AM - 8:12AM |
A18.00001: Topological Insulators / Normal Insulators Superlattices Marcio Costa , Antônio Costa , Adalberto Fazzio , Marco Buongiorno Nardelli In 1970 Esaki and Tsui proposed a solid-state artificial structure: the superlattice. The recently discovered of topological insulator materials aroused the physics community. In this work, we investigate topological / normal insulator (TI/NI) interfaces and its superlattice using a combination of DFT and a highly accurate tight biding modeling [1]. The calculations were based on the Bi_{2}Se_{3} topological insulator. The normal insulator in simply the Bi_{2}Se_{3} without spin-orbit coupling. This approach enables us to investigate a chemically perfect TI/NI interface. Experimentally these superlattices have been reported by Belopolski et. al. [2]. Initially, we investigated a hypothetical infinity TI/NI superlattice and for a large NI thickness the topologically protected states are present. We also investigate when a TI (NI) is placed between two NI(TI) regions. We also show how to used these superllattices to supress the Bi_{2}Se_{3 }bulk states, which are detrimental to its transport properties. Finally we investigate the 1D chain of Dirac states proposed by Belopolski. |
Monday, March 5, 2018 8:12AM - 8:24AM |
A18.00002: Topological Band Engineering Graphene Nanoribbons Daniel Rizzo , Greg Veber , Ting Cao , Christopher Bronner , Henry Rodriguez , Steven Louie , Michael Crommie , Felix Fisher Graphene nanoribbons (GNRs) are 1-dimensional semiconducting strips of graphene that possess novel electronic and magnetic properties. The atomic precision afforded by recent bottom-up synthetic techniques has led to a surge in tailor-made GNR structures whose physical properties can be controllably tuned through modification of width, edge chirality, and dopant incorporation. Recent theoretical work reveals the presence of non-trivial topological phases in GNRs, and correspondingly, the existence of zero-energy symmetry-protected topological interface states. Using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS), we investigate the first experimental realization of controlled heterojunctions composed of two topologically distinct GNR classes. Our approach enables us to create a periodic superlattice of topological interface states, whose bonding/anti-bonding interactions lead to the creation of two new frontier bands. This yields a drastically reduced band gap compared to either of the two constituent GNRs, revealing the powerful role topology will play in engineering new GNR electronic structures. |
Monday, March 5, 2018 8:24AM - 8:36AM |
A18.00003: Tuning the Crystalline Structure, Bandgap, and Topological Properties of 2D Fullerites via Heavy Element Doping Jiang Zeng , Wei Qin , Ping Cui , Zhenyu Zhang Well-designed two-dimensional (2D) honeycomb lattices offer a tunable platform for studying massless Dirac quasiparticles and their topological and correlated phases. The fullerene (C_{n}) molecules and fullerites have attracted enormous attention, whereas their 2D counterparts are rarely studied. Using first-principles calculations, we demonstrate that the C_{n} (n>20) fullerenes prefer the close-packing arrangement, while the heavy-element (Sb, Te, Pb, and Bi) doped C_{28} fullerenes prefer the honeycomb lattice. Generally, Dirac bands appear in the honeycomb lattices consisting of C_{n} molecules when the systems considered possess C_{3v} symmetry. In the doped systems, the bandgap opens due to two mechanisms: the spin-orbit coupling from the heavy elements and the broken mirror symmetry due to the relative rotation between the C_{n} molecules. In particular, the former mechanism may induce a topologically nontrivial phase to realize the quantum spin Hall effect. |
Monday, March 5, 2018 8:36AM - 8:48AM |
A18.00004: Lieb-Schultz-Mattis Theorem and its generalizations from the Perspective of the Symmetry Protected Topological phase Chao-Ming Jian , Zhen Bi , Cenke Xu We ask whether a local Hamiltonian with a featureless (fully gapped, nondegenerate and symmetric) ground state could exist in certain quantum spin systems. We address this question by mapping the vicinity of certain quantum critical point (or gapless phase) of the d-dimensional spin system under study to the boundary of a (d+1)-dimensional bulk state, and the lattice symmetry of the spin system acts as an on-site symmetry in the field theory that describes both the selected critical point of the spin system, and the corresponding boundary state of the (d+1)-dimensional bulk. If the symmetry action of the field theory is nonanomalous, i.e. the corresponding bulk state is a trivial state instead of a bosonic symmetry protected topological (SPT) state, then a featureless ground state of the spin system is allowed; if the corresponding bulk state is indeed a nontrivial SPT state, then it likely excludes the existence of a featureless ground state of the spin system. From this perspective we identify the spin systems with SU(N) and SO(N) symmetries on one, two and three dimensional lattices that permit a featureless ground state. |
Monday, March 5, 2018 8:48AM - 9:00AM |
A18.00005: Floquet Protocols of Adiabatic State-Flips and Re-Allocation of Exceptional Points Dashiell Halpern , Huanan Li , Tsampikos Kottos We study a non-Hermitian system which is subject to two driving schemes with clear separation of time scales. The fast modulation is used to control the topological features of an adiabatic cyclic modulation (slow driving) through the re-allocation, creation or annihilation of exceptional point. These driving scenarios lead to the novel notion of the adiabatic state-flip of a Floquet Hamiltonian, which allows for a realization of reconfigurable chiral energy transfer. The proposed scheme can find applications in system control in photonics and microwave domains. |
Monday, March 5, 2018 9:00AM - 9:12AM |
A18.00006: Nonlinear Quantum Langevin Equations for Bosonic Modes in Solid-state Systems Juuso Manninen , Souvik Agasti , Francesco Massel Based on the experimental evidence that impurities contribute to the dissipation properties of solid-state open quantum systems, we provide here a description in terms of nonlinear quantum Langevin equations of the role played by two-level systems in the dynamics of a bosonic degree of freedom. Our starting point is represented by the description of the system/environment coupling in terms of coupling to two separate reservoirs, modelling the interaction with external bosonic modes and two level systems, respectively. Furthermore, we show how this model represents a specific example of a class of open quantum systems that can be described by nonlinear quantum Langevin equations. Our analysis offers a potential explanation of the parametric effects recently observed in circuit-QED cavity optomechanics experiments. |
Monday, March 5, 2018 9:12AM - 9:24AM |
A18.00007: All-optical binary switch based on photonic topological states Juan Merlo , Michael Burns , Michael Naughton Topological photonics is an incipient research area where the well-developed theory and applications of the so-called topological insulators is applied to photonic systems [1]. In this sense, specially designed ring waveguides have shown the ability to propagate edge states scattering-free under defects on the structure [2]. In the present work, we proposed numerically the application of photonic topological states coupled, in a set of ring waveguides, to a binary switch with potential applications in on-chip Si based devices. We show that the materials and dimensions of the device can be implemented by conventional fabrication methods, and that the ON/OFF states are clearly distinguished by a ratio of ~ -7 dB. Further discussion on the proposed device shows the potential application to logical gates based on topological edge states. |
Monday, March 5, 2018 9:24AM - 9:36AM |
A18.00008: Subwavelength and directional topological waveguides in thin plates using Pseudo spin Hall Effect Rajesh Chaunsali , Chun-Wei Chen , Jinkyu Yang Inspired by the discovery of topological insulators, it is recent that the underlying topological framework is being used to design artificial structures, the so-called topological metamaterials, with the aim of controlling the flow of photons and phonons on their boundaries. In this regard, tailoring elastic waves in mechanical structures shows tremendous potential for engineering usages, such as novel sensing, energy harvesting, and impact mitigation purposes. Here, we propose a macro-scale, continuum structure to mimic pseudo spin Hall Effect at a subwavelength scale and achieve a robust and directional control of elastic waves along a designed waveguide. This structure consists of a thin continuum plate with local resonators mounted on its top. Using the plane wave expansion method and the finite element method, we show the existence of a double Dirac cone in the dispersion at low frequencies. We show that by modifying the design strategically, we can open a gap at the Dirac frequency and also achieve band inversion in the system. When two topologically distinct systems are placed adjacently, we show the existence of two pseudo-spins propagating in opposite directions at the domain wall. |
Monday, March 5, 2018 9:36AM - 9:48AM |
A18.00009: Wavelength-division multiplexed quantum key distribution on silicon photonic integrated devices Darius Bunandar , Nicholas Harris , Zheshen Zhang , Catherine Lee , Ran Ding , Tom Baehr-Jones , Michael Hochberg , Jeffrey Shapiro , Franco Wong , Dirk Englund We present a compact four-channel wavelength-division multiplexed quantum key distribution (WDM-QKD) transmitter near a 1550-nm wavelength implemented on a CMOS-compatible silicon-on-insulator photonics platform. Each channel of the transmitter consists of a ring modulator and a ring multiplexer, which acts as an add-drop filter to the quantum channel. To demonstrate the device’s performance, we generate secret keys using the coherent-one-way protocol at a collective rate higher than 1 Mbps under a novel composable security framework. Our work shows the potential of exploiting multiple wavelength channels in a compact advanced photonic integrated circuit to enable high-speed quantum-secure communications. |
Monday, March 5, 2018 9:48AM - 10:00AM |
A18.00010: Demonstration of a Bi-Anisotropic Meta-Waveguide Quantum Hall Analog Steven Anlage , Shukai Ma , Bo Xiao , Kueifu Lai , Tzuhsuan Ma , Gennady Shvets Photonic topological insulators (PTI) are a new class of structures that can support unidirectional propagating waves at a surface or interface. Inside a bulk structure of bi-anisotropic meta-waveguide (BMW), by carefully tuning the geometrical and electromagnetic properties, we can emulate the electronic quantum spin Hall (QSH) effect using its electromagnetic analog. Further, one can break the σ_{z} symmetry by opening an air gap on top of the bulk region, and introduce the bi-anisotropic response of the meta-waveguide. Both experimental and simulation efforts show that waves launched with opposite circular polarization will adopt opposite propagating direction inside the interface region of two bulk regions, thus creating a reflection-less waveguide. We next construct a quantum Hall (QH) analog BMW structure that breaks time-reversal invariance. By replacing the symmetry-breaking air gap with magnetized garnet ferrite components, theoretical studies show that an interface of the QH/QSH regions will guide the wave propagating only along one direction. We also demonstrate a 4-port circulator with high transmission efficiency based on a composite quantum spin-Hall and quantum Hall BMW structure. |
Monday, March 5, 2018 10:00AM - 10:12AM |
A18.00011: Optical Selection Rule of Excitons in Gapped Chiral Fermion Systems Xiaoou Zhang , Wen-Yu Shan , Di Xiao We show that the exciton optical selection rule in gapped chiral fermion systems is governed by their winding number w, a topological quantity of the Bloch bands. Specifically, in a C_{N}-invariant chiral fermion system, the angular momentum of bright exciton states is given by w ± 1 + nN with n being an integer. We demonstrate our theory by proposing two chiral fermion systems capable of hosting dark s-like excitons: gapped surface states of a topological crystalline insulator with C_{4} rotational symmetry and biased 3R-stacked MoS_{2} bilayers. In the latter case, we show that gating can be used to tune the s-like excitons from bright to dark by changing the winding number. Our theory thus provides a pathway to electrical control of optical transitions in two-dimensional material. |
Monday, March 5, 2018 10:12AM - 10:24AM |
A18.00012: MEMS-Driven Reconfigurable Metamaterial Waveplate at Terahertz Frequencies Xiaoguang Zhao , Jacob Schalch , Jingdi Zhang , Guangwu Duan , Richard Averitt , Xin Zhang Dynamic polarization control of light is essential for numerous applications ranging from imaging to materials characterization. We present a reconfigurable terahertz metamaterial quarter-waveplate consisting of microelectromechanical systems (MEMS) cantilever actuators. The anisotropic response of the metamaterial enables polarization conversion of the transmitted waves. Specifically, electromechanical actuation of the cantilevers provides polarization selective control of the resonance frequency, enabling real-time tuning of the polarization state of the transmitted light. The polarization tunable metamaterial has been fabricated using surface micromachining and characterized using terahertz time domain spectroscopy. We obtained a ~230 GHz frequency shift of the resonance mode, modulating the transmitted wave from pure circular polarization to linear polarization at 0.8 THz with 50% amplitude variations. This work informs possibilities for real-time control of electromagnetic waves using engineered dynamic metamaterials. |
Monday, March 5, 2018 10:24AM - 10:36AM |
A18.00013: Bianisotropic all-dielectric metasurfaces for efficient diffraction of mid infrared electromagnetic waves Zhiyuan Fan , Maxim Shcherbakov , Gennady Shvets A blazed grating maximizes the diffraction efficiency in a specific diffraction order. We design and experimentally demonstrate a bianisotropic all-silicon metasurface that shows a near unity diffraction efficiency by implementing a 4-mode interference in the far field. A coupled mode analysis shows that these modes provide a small number of orthogonal radiative electromagnetic moments that are needed for a perfect blazed grating. Bianisotropy due to asymmetric meta-atoms allows a normally incident plane wave to access through near field couplings two other modes which would have vanishing dipole moments without the symmetry breaking. Resonant and non-resonant properties of these modes and respective interaction can be mediated by sculpting meta-atoms of the metasurface. Because of these low order electromagnetic moments being utilized for the blazed grating, these high index meta-atoms can be subwavelength in all dimensions using simple geometries. At the same time, optical properties of these modes are relatively less sensitive to local fabrication imperfections. Further numerical simulations show an array consisting of a small number of these meta-atoms can efficiently diffract tightly focused Gaussian beams. |
Monday, March 5, 2018 10:36AM - 10:48AM |
A18.00014: Coupling of terahertz split-ring resonators to antiferromagnetic resonances in CaFe_{2}O_{4} Daniel Heligman , Thuc Mai , Alex Potts , Matthew Warren , Rolando Valdes Aguilar Most terahertz (THz) metamaterial studies have focused on their electromagnetic response without considering their interaction with the substrate. We study the possible interaction between split-ring resonator metamaterials grown on the novel antiferromagnet CaFe_{2}O_{4} to the antiferromagnetic resonances in CaFe_{2}O_{4}. This material exhibits two resonances at low temperature around ~600GHz and ~700GHz for different crystal orientations, which are detected with THz spectroscopy by properly polarizing the electromagnetic wave along the different crystal axes. We design and match the resonant frequency of the split-ring resonators to those of the magnons in CaFe_{2}O_{4}. We test the interaction between the magnetic split-ring resonator response and the antiferromagnetic resonances by varying the distance between the antiferromagnet and the metamaterial. This is done by adding an insulating layer of photoresist in between them. We report on the results of these tests. |
Monday, March 5, 2018 10:48AM - 11:00AM |
A18.00015: Analyzing the absorption peak frequency of metamaterial absorber Guangwu Duan , Jacob Schalch , Xiaoguang Zhao , Jingdi Zhang , Richard Averitt , Xin Zhang Metamaterial absorbers typically consist of a layer of split ring resonators (SRRs), a dielectric spacer layer, and a metallic ground plane. We have investigated the effect of both the spacer layer thickness and the SRR resonant frequency on the absorption peak frequencies. We find that by neglecting the coupling between the metamaterials and the ground plane, the absorption peak frequencies start at the resonant frequencies of the SRRs in the limit of zero spacer thickness and undergo a red shift as the spacer thickness increases. Furthermore, for a given frequency, absorption peaks can periodically be achieved as the phase delay in the spacer approaches integer multiples of 2 pi. Moreover, we find that the absorption peak frequency shift due to the variation of spacer permittivity originates predominately from the real part rather than the imaginary part. Our findings can be applied to guide metamaterial absorber design and understand the absorption peak frequency shift of sensors based on metamaterial absorbers. |
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