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Intermediate superexponential localization with Aubry-André chains

Physical Review B 2023年第6期108卷 064204-064204页

作者： Arindam Mallick Alexei Andreanov Sergej Flach Center for Theoretical Physics of Complex Systems Institute for Basic Science (IBS) Daejeon 34126 Republic of Korea Instytut Fizyki Teoretycznej Uniwersytet Jagielloński Łojasiewicza 11 30-348 Kraków Poland Basic Science Program Korea University of Science and Technology (UST) Daejeon 34113 Korea

We demonstrate the existence of an intermediate superexponential localization regime for eigenstates of the Aubry-André chain. In this regime, the eigenstates localize similar to the eigenstates of the wannier-Stark ladder. The superexponential decay emerges on intermediate length scales for large values of the winding length—the quasiperiod of the Aubry-André potential. This intermediate length scale localization is present both in the metallic and insulating phases of the system. In the insulating phase, the superexponential localization is periodically interrupted by weaker decaying tails to form the conventional asymptotic exponential decay predicted for the Aubry-André model. In the metallic phase, the superexponential localization is only a transient phenomena and happens for states with energies away from the center of the spectrum and is followed by a superexponential growth into the next peak of the extended eigenstate. By adjusting the parameters, it is possible to extend the range of the superexponential localization to arbitrarily low values of the eigenfunction's amplitude. A similar intermediate superexponential localization regime is demonstrated in quasiperiodic discrete-time unitary maps.

关键词： Anderson localization Atomic & molecular processes in external fields Charge Cold atoms & matter waves Cold gases in optical lattices Crystal phenomena Defects Hopping transport Lattice dynamics Localization Optical lattices & traps Phase transitions Quantum interference effects Quantum transport Stark effect 1-dimensional systems Atomic gases Floquet systems Insulators Quantum crystals Quantum fluids & solids Quasicrystals Random & disordered media Single-electron devices Trapped ions Ultracold gases Electric moment Polarizability Polarization Discrete symmetries in condensed matter Lattice models in condensed matter Schroedinger equation Strong-field approximation Tight-binding model Two-level models wannier function methods

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Unambiguous and robust formulation for wannier localization

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Physical Review B 2024年第8期110卷 085127-085127页

作者： Kangbo Li Hsin-Yu Ko Robert A. DiStasio, Jr. Anil Damle Department of Computer Science Department of Chemistry and Chemical Biology

We provide a new variational definition for the spread of an orbital under periodic boundary conditions (PBCs) that is continuous with respect to the gauge, consistent in the thermodynamic limit, well suited to diffuse orbitals, and systematically adaptable to schemes computing localized wannier functions. Existing definitions do not satisfy all these desiderata, partly because they depend on an “orbital center”—an ill-defined concept under PBCs. Based on this theoretical development, we showcase a robust and efficient (10×–70× fewer iterations) localization scheme across a range of materials.

关键词： Electronic structure Density functional calculations wannier function methods

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Plane-wave many-body corrections to the conductance in bulk tunnel junctions

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Physical Review B 2020年第7期101卷 075402-075402页

作者： Alberto Dragoni Benoît Sklénard Valerio Olevano François Triozon CEA LETI MINATEC Campus 38054 Grenoble France Université Grenoble Alpes 38000 Grenoble France CNRS Institut Néel 38042 Grenoble France

The conductance of bulk metal–insulator–metal junctions is evaluated by the Landauer formula using an ab initio electronic structure calculated using a plane-wave basis set within density functional theory and beyond, i.e., including exact nonlocal exchange using hybrid functional (HSE) or many-body G0W0 and Coulomb-hole screened exchange (COHSEX) quasiparticle schemes. We consider an Ag/MgO/Ag heterostructure model and we focus on the evolution of the zero-bias conductance as a function of the MgO film thickness. Our study shows that the correction of the electronic structure beyond semilocal density functionals goes in the right direction to improve the agreement with experiments, significantly reducing the zero-bias conductance. This effect becomes more evident at larger MgO thickness, that is, in increasing tunneling regime. We also observe that the reduction of the conductance seems more related to the correction of wave functions rather than energies, and thus not directly related to the correction of the band gap of bulk MgO. G0W0 and HSE both provide a band gap in agreement with experiments, but only HSE gives a significant reduction of the conductance. COHSEX, while overestimating the band gap, gives a reduction of the conductance very close to HSE.

关键词： Ballistic transport Band gap Electronic structure Electronic structure of atoms & molecules Transport phenomena Tunnel junctions Density functional calculations Density functional theory First-principles calculations GW method Hybrid functionals Landauer formula Many-body techniques Numerical approximation & analysis wannier function methods

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Revealing the Complex Nature of Bonding in the Binary High-Pressure Compound FeO2

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Physical Review Letters 2021年第10期126卷 106001-106001页

作者： E. Koemets I. Leonov M. Bykov E. Bykova S. Chariton G. Aprilis T. Fedotenko S. Clément J. Rouquette J. Haines V. Cerantola K. Glazyrin C. McCammon V. B. Prakapenka M. Hanfland H.-P. Liermann V. Svitlyk R. Torchio A. D. Rosa T. Irifune A. V. Ponomareva I. A. Abrikosov N. Dubrovinskaia L. Dubrovinsky Bayerisches Geoinstitut University of Bayreuth D-95440 Bayreuth Germany Institut Charles Gerhardt Montpellier (UMR CNRS 5253) Université de Montpellier F-34095 Montpellier Cedex 5 France Institute of Metal Physics Sofia Kovalevskaya Street 18 620219 Yekaterinburg GSP-170 Russia Materials Modeling and Development Laboratory NUST “MISIS” 119049 Moscow Russia Ural Federal University 620002 Yekaterinburg Russia Carnegie Institution of Washington Earth and Planets Laboratory 5241 Broad Branch Road NW Washington DC 20015 USA Material Physics and Technology at Extreme Conditions Laboratory of Crystallography Universität Bayreuth D-95440 Bayreuth Germany The European Synchrotron Radiation Facility 38043 Grenoble Cedex 9 France Laboratoire Charles Coulomb (L2C)—UMR CNRS 5221 Université de Montpellier CC069 34095 Montpellier France Photon Science Deutsches Elektronen-Synchrotron D-22607 Hamburg Germany Center for Advanced Radiation Sources University of Chicago Chicago Illinois 60437 USA Geodynamics Research Center Ehime University 2-5 Bunkyo-cho Matsuyama 790-8577 Japan Department of Physics Chemistry and Biology (IFM) Linköping University SE-581 83 Linköping Sweden

Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe2O3 and the appearance of FeO2. Here, based on the results of in situ single-crystal x-ray diffraction, Mössbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory+dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO2 and isostructural FeO2H0.5 is ferric (Fe3+), and oxygen has a formal valence less than 2. Reduction of oxygen valence from 2, common for oxides, down to 1.5 can be explained by a formation of a localized hole at oxygen sites.

关键词： Chemical bonding Crystal structure Density of states Earth's interior Electronic structure of atoms & molecules Inorganic chemistry Pressure effects Solid-state chemistry Structural properties Crystal structures Strongly correlated systems DFT+DMFT Mössbauer spectroscopy wannier function methods X-ray absorption near-edge spectroscopy X-ray diffraction

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Symmetry-guaranteed ideal Weyl semimetallic phase in face-centered orthogonal C6

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Physical Review B 2020年第23期101卷 235119-235119页

作者： Chao Zhang Xian-Yong Ding Li-Yong Gan Yu Cao Bing-Sheng Li Xiaozhi Wu Rui Wang School of Materials Science and Engineering Anhui University of Science and Technology Huainan 232001 People's Republic of China State Key Laboratory for Environment-Friendly Energy Materials Southwest University of Science and Technology Mianyang Sichuan 621010 People's Republic of China Department of Physics Institute for Structure and Function Chongqing University Chongqing 400044 People's Republic of China Center for Quantum Materials and Devices Chongqing University Chongqing 400044 People's Republic of China

The exploration of topological phases in carbon allotropes is always an attractive topic. Here, we propose a metastable carbon allotrope, which possesses exotically helical carbon chains bridged by quadrangle rings. This unique structure with sp2−sp3 bonding networks crystallizes in a noncentrosymmetric face-centered orthogonal (fco) lattice with six atoms in a unit cell, thus, named fco−C6. This carbon phase possesses the considerable stability, thus, facilitating its experimental fabrication. More importantly, fco−C6 exhibits ideal Weyl semimetallic features with the minimum number of Weyl points in a time-reversal system. First-principles calculations and symmetry arguments uncover that the Weyl points are guaranteed to lie along the high-symmetry paths, and thus well separated in momentum space. We investigate the topological surface states of fco−C6 projected on a semi-infinite (010) surface. There are only two extremely long Fermi arcs across the projected Fermi surface. Therefore, this paper provides an ideal candidate to detect Weyl fermions and can realize further applications in carbon allotropes.

关键词： Topological materials Carbon-based materials Weyl semimetal First-principles calculations wannier function methods k dot p method

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Z2 topology of bismuth

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Physical Review Materials 2021年第9期5卷 L091201-L091201页

作者： Irene Aguilera Hyun-Jung Kim Christoph Friedrich Gustav Bihlmayer Stefan Blügel Peter Grünberg Institute and Institute for Advanced Simulation Forschungszentrum Jülich and JARA 52425 Jülich Germany

While first-principles calculations with different levels of sophistication predict a topologically trivial Z2 state for bulk bismuth, some photoemission experiments show surface states consistent with the interpretation of bismuth being in a topologically nontrivial Z2 state. We resolve this contradiction between theory and experiment by showing, based on quasiparticle self-consistent GW calculations, that the experimental surface states interpreted as supporting a nontrivial phase are actually consistent with a trivial Z2 invariant. We identify this contradiction as the result of a crosstalk effect arising from the extreme penetration depth of the surface states into the bulk of Bi. A film of Bi can be considered bulklike only for thicknesses of about 1000 bilayers (≈400 nm) and more.

关键词： First-principles calculations Surface states Topological phases of matter Topological materials GW method Tight-binding model wannier function methods

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Topological half-metallic features in alkali metal doped CrCl3 monolayers

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Physical Review B 2023年第17期107卷 174405-174405页

作者： Fei Wang Yaling Zhang Wenjia Yang Jingjing Zhang Huisheng Zhang Xiaohong Xu Key Laboratory of Magnetic Molecules and Magnetic Information Materials of the Ministry of Education and Research Institute of Materials Science Shanxi Normal University Taiyuan 030006 China College of Physics and Electronic Information Shanxi Normal University Taiyuan 030006 China

Two-dimensional (2D) topological half metals, namely, empowering nontrivial topological states with 100% spin-polarized 2D systems, may find important applications in low-dissipation spintronics. However, exploration of such intriguing materials is still very challenging. The recently discovered 2D magnetic materials provide unprecedented opportunities to realize 2D topological half-metallic state. Using first-principles calculations, we first find that the ferromagnetism of CrCl3 monolayer can be well reserved by doping alkali metals, in fact, whose Curie temperature can be enhanced from 23 to 66 K after doping K. Then, we notice that semiconducting to Dirac half-metallic phase transition is achieved via Na and K doping, where the linear Dirac dispersion originates from the honeycomb lattice formed by Cr atoms. Most strikingly, Na- and K doped CrCl3 exhibit quantum anomalous Hall effect (QAHE) with Chern number C=1, while the Li-doped one harbors high Chern number QAHE with C=−2. Thus, our work provides a theoretical guideline to realize 2D topological half-metallic state, rendering it as a promising platform for future applications.

关键词： Phase transitions Spintronics 2-dimensional systems Ferromagnets Topological materials Density functional theory Monte Carlo methods Tight-binding model wannier function methods

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Coexistence of spontaneous polarization and superconductivity in hole-doped oxyhydrides ATiO2H (A=K,Rb,Cs): First-principles study

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Physical Review Materials 2021年第5期5卷 054802-054802页

作者： Minjae Ghim Nobuya Sato Ryosuke Akashi Seung-Hoon Jhi Shinji Tsuneyuki Department of Physics Pohang University of Science and Technology Pohang 37673 Republic of Korea Department of Physics The University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-0033 Japan The Institute for Solid State Physics The University of Tokyo 5-1-5 Kashiwanoha Kashiwa-shi Chiba 277-8581 Japan

Polar metal is a material that hosts both polar distortion and metallicity. Such a material is expected to show exotic magneto-electric phenomena if it superconducts. Here, we theoretically explore ferroelectric and superconducting properties in a series of perovskite-type oxyhydrides ATiO2H (A=K, Rb, Cs) under hole-doping conditions using first-principles calculations based on density functional theory. Our simulation shows that these compounds host spontaneous polarization and superconductivity at optimal doping concentration. The unusual coexistence of superconductivity and large polarization (∼100μC/cm2) originates from the weak coupling of the polar distortion and superconducting states, the reason for which is the separation of the displaced atoms and spatially confined metallic carriers. Additionally, superconductivity is enhanced by the unique electronic properties near the valence band maximum: quartic band dispersion with a sizable contribution of hydrogen 1s states. This paper thus features the oxyhydrides as possible model polar superconducting systems, which may be utilizable for future magneto-electric devices.

关键词： Electric polarization Superconductivity Electronically polarized systems Low-temperature superconductors Two-dimensional electron system BCS theory Density functional theory wannier function methods

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Ab initio derivation of an effective Hamiltonian for the La2CuO4/La1.55Sr0.45CuO4 heterostructure

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Physical Review B 2019年第15期99卷 155148-155148页

作者： Terumasa Tadano Yusuke Nomura Masatoshi Imada International Center for Young Scientists (ICYS) National Institute for Materials Science Tsukuba 305-0047 Japan Research and Services Division of Materials Data and Integrated System (MaDIS) National Institute for Materials Science Tsukuba 305-0047 Japan Department of Applied Physics The University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8656 Japan

We formulate a method of deriving an effective low-energy Hamiltonian for nonperiodic systems such as interfaces for strongly correlated electron systems by extending a conventional multiscale ab initio scheme for correlated electrons (MACE). We apply the formalism to copper-oxide high Tc superconductors in an example of the interface between overdoped La2−xSrxCuO4 and Mott insulating La2CuO4 recently realized experimentally and derive the two-band effective Hamiltonian (Eg Hamiltonian) from the Cu 3dx2−y2-like and 3d3r2−z2-like orbitals near the Fermi level. We show that the parameters of the Eg Hamiltonian derived for the La2CuO4/La1.55Sr0.45CuO4 superlattice differ considerably from those for the bulk La2CuO4, particularly significant in the partially screened Coulomb parameters and the level offset between the dx2−y2 and dz2 orbitals, ΔE. In addition, we investigate the effect of the lattice relaxation on the Eg Hamiltonian by carefully comparing the parameters derived before and after the structure optimization. We find that the CuO6 octahedra distort after the relaxation as a consequence of the Madelung potential difference between the La2CuO4 and La1.55Sr0.45CuO4 sides, by which the layer dependence of the hopping and Coulomb parameters becomes more gradual than the unrelaxed case. Furthermore, the structure relaxation dramatically changes the ΔE value and the occupation number at the interface. This study not only evidences the importance of the ionic relaxation around interfaces but also provides a set of layer-dependent parameters of the Eg Hamiltonian, which is expected to provide further insight into the interfacial superconductivity when solved with low-energy solvers.

关键词： First-principles calculations Cuprates Interfaces Random phase approximation wannier function methods

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Spread-balanced wannier functions: Robust and automatable orbital localization

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Physical Review B 2021年第12期104卷 125140-125140页

作者： Pietro F. Fontana Ask H. Larsen Thomas Olsen Kristian S. Thygesen CAMD Department of Physics Technical University of Denmark DK-2800 Kongens Lyngby Denmark

We introduce a type of wannier functions (WFs) obtained by minimizing the conventional spread functional with a penalty term proportional to the variance of the spread distribution. This modified wannierization scheme is less prone to produce ineffective solutions featuring one or several poorly localized orbitals, making it well suited for complex systems or high-throughput applications. Furthermore, we propose an automatable protocol for selecting the initial guess and determine the optimal number of bands (or equivalently, WFs) for the localization algorithm. The improved performance and robustness of the approach is demonstrated for a diverse set of test systems including the nitrogen-vacancy center in diamond, metal slabs with atomic adsorbates, spontaneous polarization of ferroelectrics, and 30 inorganic monolayer materials comprising both metals and semiconductors. The methods are implemented in Python as part of the Atomic Simulation Environment.

关键词： First-principles calculations Density functional theory wannier function methods

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