Institute of Physics Belgrade

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A guide to hunting periodic three-body orbits with non-vanishing angular momentum
Janković, Marija; Dmitrašinović, Veljko; Šuvakov, Milovan
A large number of periodic three-body orbits with vanishing angular momentum have been found in Newtonian gravity over the past 6 years due to a simple search method and to the contribution from practitioners outside the Celestial Mechanics community. Extension of such orbits to non-vanishing angular momentum has been lacking due to inter alia the absence of a sufficiently simple and widely known search method. We present a method, i.e., a general strategy plus detailed tactics (but not a specific algorithm, or a code), to numerically search for relative periodic orbits in the Newtonian three-body problem with three equal masses and non-vanishing angular momentum. We illustrate the method with an application to a specific, so-called Broucke–Hadjidemetriou–Hénon (BHH) family of periodic 3-body orbits: Our search yielded around 100 new “satellite” orbits, related to the original BHH orbits by a topological relation (defined in the text), with infinitely many orbits remaining to be discovered. We used the so-obtained orbits to test the period vs. topology relation that had previously been established, within a certain numerical accuracy, for orbits with vanishing angular momentum. Our method can be readily: (1) applied to families of periodic 3-body orbits other than the BHH one; (2) implemented using various standard algorithms for solving ordinary differential equations, such as the Bulirsch–Stoer and the Runge–Kutta–Fehlberg ones; (3) adapted to 3-body systems with distinct masses and/or coupling constants, including, but not limited to, Coulomb interaction. Our goal is to enable numerical searches for new orbits in as many families of orbits as possible, and thus to allow searches for other empirical relations, such as the aforementioned topology vs. period one.
A non-autonomous mega-extreme multistable chaotic system
Ahmadi, Atefeh; Parthasarathy, Sriram; Natiq, Hayder; Jafari, Sajad; Franović, Igor; Rajagopal, Karthikeyan
Megastable and extreme multistable systems comprise two major new branches of multistable systems. So far, they have been studied separately in various chaotic systems. Nevertheless, to the best of our knowledge, no chaotic system has so far been reported that possesses both types of multistability. This paper introduces the first three-dimensional non-autonomous chaotic system that displays megastability and extreme multistability, jointly called mega-extreme multistability. Our model shows extreme multistability for a variation of an initial condition associated with one system variable and megastability concerning another variable. The different types of coexisting attractors are characterized by the corresponding phase portraits and first return maps, as well as by constructing the appropriate bifurcation diagrams, calculating the Lyapunov spectra, the Kaplan-Yorke dimension and the connecting curves, and by determining the corresponding basins of attraction. The system is explicitly shown to be dissipative, with the dissipation being state-dependent. We demonstrate the feasibility and applicability of our model by designing and simulating an appropriate analog circuit.
A platform for nanomagnetism – assembled ferromagnetic and antiferromagnetic dipolar tubes
Stanković, Igor; Dašić, Miljan; Otálora, Jorge A.; García, Carlos
We report an interesting case where magnetic phenomena can transcend mesoscopic scales. Our system consists of tubes created by the assembly of dipolar spheres. The cylindrical topology results in the breakup of degeneracy observed in planar square and triangular packings. As far as the ground state is concerned, the tubes switch from circular to axial magnetization with increasing tube length. All magnetostatic properties found in magnetic nanotubes, in which the dipolar interaction is comparable to or dominant over the exchange interaction, are reproduced by the dipolar tubes including an intermediary helically magnetized state. Besides, we discuss the antiferromagnetic phase resulting from the square arrangement of the dipolar spheres and its interesting vortex state.
A three-dimensional view of Gomez’s hamburger
Teague, Richard; Jankovic, Marija R.; Haworth, Thomas J.; Qi, Chunhua; Ilee, John D.
Unravelling the three-dimensional physical structure, the temperature and density distribution, of protoplanetary discs is an essential step if we are to confront simulations of embedded planets or dynamical instabilities. In this paper, we focus on submillimeter array observations of the edge-on source, Gomez’s Hamburger, believed to host an overdensity hypothesized to be a product of gravitational instability in the disc, GoHam b. We demonstrate that, by leveraging the well-characterized rotation of a Keplerian disc to deproject observations of molecular lines in position-position-velocity space into disc-centric coordinates, we are able to map out the emission distribution in the (r,z) plane and (⁠x,|y|,z) space. We show that 12CO traces an elevated layer of z/r∼0.3⁠, while 13CO traces deeper in the disc at z/r≲0.2⁠. We identify an azimuthal asymmetry in the deprojected 13CO emission coincident with GoHam b at a polar angle of ≈30○. At the spatial resolution of ∼1.5 arcsec, GoHam b is spatially unresolved, with an upper limit to its radius of <190 au.
Ab Initio Construction of Symmetry-adapted kÂ·p Hamiltonians for the Electronic Structure of Semiconductors
Jocić, Milan; Vukmirović, Nenad
While k·p Hamiltonians are frequently used for the description of electronic states in quantum nanostructures, a method is lacking to obtain them in their symmetrized form directly from ab initio band structure calculations of bulk material. We developed a method for obtaining the parameters and the symmetry-adapted form of the k·p Hamiltonian from the output of an ab initio band structure calculation. The method consists of (i) evaluation of momentum matrix elements between the wave functions obtained from band structure calculation; (ii) identification of the unitary transformation that transforms these wave functions to the symmetry-adapted basis; (iii) transformation of the k·p Hamiltonian to the symmetry-adapted basis. We illustrate the methodology by obtaining k·p Hamiltonians that describe the band structure of zinc-blende CdSe and then we use the Hamiltonians obtained to calculate the electronic states in CdSe quantum wells. Excellent agreement between density functional theory and k·p is obtained for the electronic structure, even for quite thin wells.
Ab-initio calculations of temperature dependent electronic structures of inorganic halide perovskite materials
Jocić, Milan; Vukmirović, Nenad
Despite wide interest in halide perovskite materials, it is still challenging to accurately calculate their electronic structure and its temperature dependence. In this work, we present ab-initio calculations of the temperature dependence of the electronic structure of CsPbX3 materials (X = Cl, Br or I) in the cubic form and of the zero temperature electronic structure of the orthorhombic phase of these materials. Phonon-induced temperature dependent band energy renormalization was calculated within the framework of Allen-Heine-Cardona theory, where we exploited the self-consistent procedure to determine both the energy level shifts and their broadenings. The phonon spectrum of the materials was obtained using the self-consistent phonon method since standard density functional perturbation theory calculations in harmonic approximation yield phonon modes with imaginary frequencies due to the fact that the cubic structure is not stable at zero temperature. Our results suggest that low energy phonon modes mostly contribute to phonon-induced band energy renormalization. The calculated values of the band gaps at lowest temperature where the material exhibits a cubic structure are in good agreement with experimental results from the literature. The same is the case for the slope of the temperature dependence of the band gap for the CsPbI3 material where reliable experimental data are available in the literature. We also found that phonon-induced temperature dependence of the band gap is most pronounced for the conduction band minimum and valence band maximum, while other bands exhibit a weaker dependence.
AEDGE: Atomic Experiment for Dark Matter and Gravity Exploration in Space
El-Neaj, Yousef Abou; Alpigiani, Cristiano; Amairi-Pyka, Sana; Araújo, Henrique; Balaž, Antun; Bassi, Angelo; Bathe-Peters, Lars; Battelier, Baptiste; Belić, Aleksandar; Bentine, Elliot; Bernabeu, José; Bertoldi, Andrea; Bingham, Robert; Blas, Diego; Bolpasi, Vasiliki; Bongs, Kai; Bose, Sougato; Bouyer, Philippe; Bowcock, Themis; Bowden, William; Buchmueller, Oliver; Burrage, Clare; Calmet, Xavier; Canuel, Benjamin; Caramete, Laurentiu-Ioan; Carroll, Andrew; Cella, Giancarlo; Charmandaris, Vassilis; Chattopadhyay, Swapan; Chen, Xuzong; Chiofalo, Maria Luisa; Coleman, Jonathon; Cotter, Joseph; Cui, Yanou; Derevianko, Andrei; De Roeck, Albert; Đorđević, Goran S.; Dornan, Peter; Doser, Michael; Drougkakis, Ioannis; Dunningham, Jacob; Dutan, Ioana; Easo, Sajan; Elertas, Gedminas; Ellis, John; El Sawy, Mai; Fassi, Farida; Felea, Daniel; Feng, Chen-Hao; Flack, Robert; Foot, Chris; Fuentes, Ivette; Gaaloul, Naceur; Gauguet, Alexandre; Geiger, Remi; Gibson, Valerie; Giudice, Gian; Goldwin, Jon; Grachov, Oleg; Graham, Peter W.; Grasso, Dario; van der Grinten, Maurits; Gündogan, Mustafa; Haehnelt, Martin G.; Harte, Tiffany; Hees, Aurélien; Hobson, Richard; Hogan, Jason; Holst, Bodil; Holynski, Michael; Kasevich, Mark; Kavanagh, Bradley J.; von Klitzing, Wolf; Kovachy, Tim; Krikler, Benjamin; Krutzik, Markus; Lewicki, Marek; Lien, Yu-Hung; Liu, Miaoyuan; Luciano, Giuseppe Gaetano; Magnon, Alain; Mahmoud, Mohammed Attia; Malik, Sarah; McCabe, Christopher; Mitchell, Jeremiah; Pahl, Julia; Pal, Debapriya; Pandey, Saurabh; Papazoglou, Dimitris; Paternostro, Mauro; Penning, Bjoern; Peters, Achim; Prevedelli, Marco; Puthiya-Veettil, Vishnupriya; Quenby, John; Rasel, Ernst; Ravenhall, Sean; Ringwood, Jack; Roura, Albert; Sabulsky, Dylan; Sameed, Muhammed; Sauer, Ben; Schäffer, Stefan Alaric; Schiller, Stephan; Schkolnik, Vladimir; Schlippert, Dennis; Schubert, Christian; Sfar, Haifa Rejeb; Shayeghi, Armin; Shipsey, Ian; Signorini, Carla; Singh, Yeshpal; Soares-Santos, Marcelle; Sorrentino, Fiodor; Sumner, Timothy; Tassis, Konstantinos; Tentindo, Silvia; Tino, Guglielmo Maria; Tinsley, Jonathan N.; Unwin, James; Valenzuela, Tristan; Vasilakis, Georgios; Vaskonen, Ville; Vogt, Christian; Webber-Date, Alex; Wenzlawski, André; Windpassinger, Patrick; Woltmann, Marian; Yazgan, Efe; Zhan, Ming-Sheng; Zou, Xinhao; Zupan, Jure
We propose in this White Paper a concept for a space experiment using cold atoms to search for ultra-light dark matter, and to detect gravitational waves in the frequency range between the most sensitive ranges of LISA and the terrestrial LIGO/Virgo/KAGRA/INDIGO experiments. This interdisciplinary experiment, called Atomic Experiment for Dark Matter and Gravity Exploration (AEDGE), will also complement other planned searches for dark matter, and exploit synergies with other gravitational wave detectors. We give examples of the extended range of sensitivity to ultra-light dark matter offered by AEDGE, and how its gravitational-wave measurements could explore the assembly of super-massive black holes, first-order phase transitions in the early universe and cosmic strings. AEDGE will be based upon technologies now being developed for terrestrial experiments using cold atoms, and will benefit from the space experience obtained with, e.g., LISA and cold atom experiments in microgravity. KCL-PH-TH/2019-65, CERN-TH-2019-126.
Aerosol Synthesis and Gas-Phase Photoelectron Spectroscopy of Ag-Bi-I Nanosystems
Danilović, Danijela; Božanić, Dušan; Dojčilović, Radovan; Vukmirović, Nenad; Sapkota, Pitambar; Vukašinović, Ivana; Đoković, Vladimir; Bozek, John; Nicolas, Christophe; Ptasinska, Sylwia; Milosavljević, Aleksandar
We report on the aerosol generation of ligand-free silver iodobismuthate (Ag-Bi-I) nanoparticles (NPs) and on in situ investigation of their electronic structure using synchrotron radiation soft X-ray aerosol photoelectron spectroscopy (XAPS). The structural and morphological characterizations revealed the aerosol to be composed of spherical rudorffite Ag3BiI6 particles, approximately 100 nm in size. The XAPS showed well-resolved signals from all expected elements (Ag, Bi, and I) and allowed estimation of the NP work function to be about 4.5 eV. The ionization energy of Ag3BiI6 NPs was determined to be 6.1 eV that is in good agreement with our calculations based on a hybrid functional approach. The presented method of production of Ag3BiI6 aerosol can prove beneficial for the future development of Ag-Bi-I-based photovoltaic materials, since it allows the deposition of Ag-Bi-I particles on large surface areas of arbitrary shape and roughness.
Analysis of Worldwide Time-Series Data Reveals Some Universal Patterns of Evolution of the SARS-CoV-2 Pandemic
Mitrović Dankulov, Marija; Tadić, Bosiljka; Melnik, Roderick
Predicting the evolution of the current epidemic depends significantly on understanding the nature of the underlying stochastic processes. To unravel the global features of these processes, we analyse the world data of SARS-CoV-2 infection events, scrutinising two 8-month periods associated with the epidemic’s outbreak and initial immunisation phase. Based on the correlation-network mapping, K-means clustering, and multifractal time series analysis, our results reveal several universal patterns of infection dynamics, suggesting potential predominant drivers of the pandemic. More precisely, the Laplacian eigenvectors localisation has revealed robust communities of different countries and regions that break into clusters according to similar profiles of infection fluctuations. Apart from quantitative measures, the immunisation phase differs significantly from the epidemic outbreak by the countries and regions constituting each cluster. While the similarity grouping possesses some regional components, the appearance of large clusters spanning different geographic locations is persevering. Furthermore, characteristic cyclic trends are related to these clusters; they dominate large temporal fluctuations of infection evolution, which are prominent in the immunisation phase. Meanwhile, persistent fluctuations around the local trend occur in intervals smaller than 14 days. These results provide a basis for further research into the interplay between biological and social factors as the primary cause of infection cycles and a better understanding of the impact of socio-economical and environmental factors at different phases of the pandemic.
Analytical solution for time integrals in diagrammatic expansions: Application to real-frequency diagrammatic Monte Carlo
Vučičević, Jakša; Stipsić, Pavle; Ferrero, Michel
Recent years have seen a revived interest in the diagrammatic Monte Carlo (DiagMC) methods for interacting fermions on a lattice. A promising recent development allows one to now circumvent the analytical continuation of dynamic observables in DiagMC calculations within the Matsubara formalism. This is made possible by symbolic algebra algorithms, which can be used to analytically solve the internal Matsubara frequency summations of Feynman diagrams. In this paper, we take a different approach and show that it yields improved results. We present a closed-form analytical solution of imaginary-time integrals that appear in the time-domain formulation of Feynman diagrams. We implement and test a DiagMC algorithm based on this analytical solution and show that it has numerous significant advantages. Most importantly, the algorithm is general enough for any kind of single-time correlation function series, involving any single-particle vertex insertions. Therefore, it readily allows for the use of action-shifted schemes, aimed at improving the convergence properties of the series. By performing a frequency-resolved action-shift tuning, we are able to further improve the method and converge the self-energy in a nontrivial regime, with only 3-4 perturbation orders. Finally, we identify time integrals of the same general form in many commonly used Monte Carlo algorithms and therefore expect a broader usage of our analytical solution.
ANN prediction of the decolourisation efficiency of the organic dyes in wastewater by plasma needle
Mitrović, Tatjana; Ristić, Mirjana; Perić-Grujić, Aleksandra; Lazović, Saša
In this paper, the results of decolourisation of Reactive Orange 16 (RO 16), Reactive Blue 19 (RB 19) and Direct Red 28 (DR 28) textile dyes in aqueous solution by plasma needle are presented. Treatment time, feed gas flow rate (1, 4 and 8 dm3 min-1) and gas composition (Ar, Ar/O2) were optimized to achieve the best performance of the plasma treatment. An artificial neural network (ANN) was used for the prediction of parameters relevant for the decolourisation outcome. It was found that more than 95 % decolourisation could be achieved for all three dyes after plasma treatment, although the decolourisation of DR 28 was much slower than those of the other two dyes, which could be explained by the complexity of its molecular structure. It was concluded that the oxidation was very dependent on all three mentioned parameters. The ANN predicted the treatment time as the crucial factor for decolourisation performance of RO 16 and DR 28, while the Ar flow rate was the most relevant for RB 19 decolourisation. The obtained results suggest that the plasma needle is a promising tool for the oxidation of organic pollutants and that an ANN could be used for optimization of the treatment parameters to achieve high removal rates.
Anomalous tracer diffusion in the presence of extended obstacles on a triangular lattice
Lončarević, Ivana; Dujak, Dijana; Jakšić, Zorica; Karač, Aleksandar; Budinski-Petković, Ljuba; Vrhovac, Slobodan
Proteins diffuse to their sites of action within cells in a crowded, strongly interacting environment of nucleic acids and other macromolecules. An interesting question is how the highly crowded environment of biological cells affects the dynamic properties of passively diffusing particles. The Lorentz model is a generic model covering many of the aspects of transport in a heterogeneous environment. We investigate biologically relevant situations of immobile obstacles of various shapes and sizes. The Monte Carlo simulations for the diffusion of a tracer particle are carried out on a two-dimensional triangular lattice. Obstacles are represented by non-overlapping lattice shapes that are randomly placed on the lattice. Our simulation results indicate that the mean-square displacement displays anomalous transport for all obstacle shapes, which extends to infinite times at the corresponding percolation thresholds. In the vicinity of this critical density the diffusion coefficient vanishes according to a power law, with the same conductivity exponent for all obstacle shapes. At the fixed density of obstacles, we observe that the diffusion coefficient is higher for the smaller obstacles if the object size is defined as the highest projection of the object on one of the six directions on the triangular lattice. The dynamic exponent, which describes the anomalous transport at the critical density, is the same for all the obstacle shapes. Here we show that the values of critical exponents estimated for all disordered environments do not depend on the microscopic details of the present model, such as obstacle shape, and agree with the predicted values for the underlying percolation problem. We also provide the evidence for a divergent non-Gaussian parameter close to the percolation transition for all obstacle shapes.
Atmospheric Plasma Supported by TiO2 Catalyst for Decolourisation of Reactive Orange 16 Dye in Water
Mitrović, Tatjana; Tomić, Nataša; Đukić-Vuković, Aleksandra; Dohčević-Mitrović, Zorana; Lazović, Saša
Purpose: Every advanced oxidation process (AOP) has its limitations in water purification. Novel designs with simultaneous application of different AOPs can offer better solutions for cleaner water. Methods: We have comparatively studied two advanced oxidation processes (AOPs) on decolourisation of Reactive Orange 16 (RO 16) azo dye pollutant from water: gas plasma treatment by low power atmospheric pressure plasma using novel plasma needle configuration, and semiconductor heterogeneous photocatalysis using titanium dioxide (TiO2) nanopowders. Additionally, simultaneous application of two advanced oxidation processes on azo dye decolourisation was studied. Results: It was found that plasma treatment is very efficient system for the dye removal even for low flow rates (1 slm) of the Ar as feed gas. The presence of 10% of O2 in Ar flow intensified dye oxidation process and shortened required time for total decolourisation. When plasma and catalyst were simultaneously applied, TiO2 was activated with a few Watts plasma source as well as 300 W UV lamp source. The synergic effect of two AOPs was more pronounced for higher feed gas flow rates, resulting in improved decolourisation efficiency. Conclusion: Plasma needle can efficiently remove Reactive Orange 16 azo dye from water with a power consumption of only few Watts. With the addition of TiO2 the removal efficiency is significantly improved.
Atomic-Level Microstructure of Efficient Formamidinium-Based Perovskite Solar Cells Stabilized by 5-Ammonium Valeric Acid Iodide Revealed by Multinuclear and Two-Dimensional Solid-State NMR
Alanazi, Anwar Q.; Kubicki, Dominik J.; Prochowicz, Daniel; Alharbi, Essa A.; Bouduban, Marine E. F.; Jahanbakhshi, Farzaneh; Mladenović, Marko; Milić, Jovana; Giordano, Fabrizio; Ren, Dan; Alyamani, Ahmed Y.; Albrithen, Hamad; Albadri, Abdulrahman; Alotaibi, Mohammad Hayal; Moser, Jacques-E.; Zakeeruddin, Shaik M.; Rothlisberger, Ursula; Emsley, Lyndon; Grätzel, Michael
Chemical doping of inorganic-organic hybrid perovskites is an effective way of improving the performance and operational stability of perovskite solar cells (PSCs). Here we use 5-ammonium valeric acid iodide (AVAI) to chemically stabilize the structure of α-FAPbI3. Using solid-state MAS NMR, we demonstrate the atomic-level interaction between the molecular modulator and the perovskite lattice and propose a structural model of the stabilized three-dimensional structure, further aided by density functional theory (DFT) calculations. We find that one-step deposition of the perovskite in the presence of AVAI produces highly crystalline films with large, micrometer-sized grains and enhanced charge-carrier lifetimes, as probed by transient absorption spectroscopy. As a result, we achieve greatly enhanced solar cell performance for the optimized AVA-based devices with a maximum power conversion efficiency (PCE) of 18.94%. The devices retain 90% of the initial efficiency after 300 h under continuous white light illumination and maximum-power point-tracking measurement.
Automatic heterogeneous quantization of deep neural networks for low-latency inference on the edge for particle detectors
Coelho, Claudionor; Kuusela, Aki; Li, Shan; Zhuang, Hao; Ngadiuba, Jennifer; Aarrestad, Thea Klaeboe; Lončar, Vladimir; Pierini, Maurizio; Pol, Adrian Alan; Summers, Sioni
Although the quest for more accurate solutions is pushing deep learning research towards larger and more complex algorithms, edge devices demand efficient inference and therefore reduction in model size, latency and energy consumption. One technique to limit model size is quantization, which implies using fewer bits to represent weights and biases. Such an approach usually results in a decline in performance. Here, we introduce a method for designing optimally heterogeneously quantized versions of deep neural network models for minimum-energy, high-accuracy, nanosecond inference and fully automated deployment on chip. With a per-layer, per-parameter type automatic quantization procedure, sampling from a wide range of quantizers, model energy consumption and size are minimized while high accuracy is maintained. This is crucial for the event selection procedure in proton–proton collisions at the CERN Large Hadron Collider, where resources are strictly limited and a latency of O(1)μs is required. Nanosecond inference and a resource consumption reduced by a factor of 50 when implemented on field-programmable gate array hardware are achieved.
Blunt-End Driven Re-entrant Ordering in Quasi Two-Dimensional Dispersions of Spherical DNA Brushes
Romero-Sanchez, Ivany; Pihlajamaa, Ilian; Adžić, Natasa; Castellano, Laura E.; Stiakakis, Emmanuel; Likos, Christos N.; Laurati, Marco
We investigate the effects of crowding on the conformations and assembly of confined, highly charged, and thick polyelectrolyte brushes in the osmotic regime. Particle tracking experiments on increasingly dense suspensions of colloids coated with ultralong double-stranded DNA (dsDNA) fragments reveal nonmonotonic particle shrinking, aggregation, and re-entrant ordering. Theory and simulations show that aggregation and re-entrant ordering arise from the combined effect of shrinking, which is induced by the osmotic pressure exerted by the counterions absorbed in neighbor brushes and of a short-range attractive interaction competing with electrostatic repulsion. An unconventional mechanism gives origin to the short-range attraction: blunt-end interactions between stretched dsDNA fragments of neighboring brushes, which become sufficiently intense for dense and packed brushes. The attraction can be tuned by inducing free-end backfolding through the addition of monovalent salt. Our results show that base stacking is a mode parallel to hybridization to steer colloidal assembly in which attractions can be fine-tuned through salinity and, potentially, grafting density and temperature.
Bridging quantum criticality via many-body scarring
Daniel, Aiden; Hallam, Andrew; Jean-Yves Desaules; Hudomal, Ana; Su, Guo-Xian; Halimeh, Jad; Papić, Zlatko
Quantum dynamics in certain kinetically-constrained systems can display a strong sensitivity to the initial condition, wherein some initial states give rise to persistent quantum revivals - a type of weak ergodicity breaking known as "quantum many-body scarring"(QMBS). Recent work [Yao, Pan, Liu, and Zhai, Phys. Rev. B 105, 125123 (2022)2469-995010.1103/PhysRevB.105.125123] pointed out that QMBS gets destroyed by tuning the system to a quantum critical point, echoing the disappearance of long-range order in the system's ground state at equilibrium. Here we show that this picture can be much richer in systems that display QMBS dynamics from a continuous family of initial conditions: As the system is tuned across the critical point while at the same time deforming the initial state, the dynamical signatures of QMBS at intermediate times can undergo an apparently smooth evolution across the equilibrium phase transition point. We demonstrate this using the PXP model - a paradigmatic model of QMBS that has recently been realized in Rydberg atom arrays as well as ultracold bosonic atoms in a tilted optical lattice. Using exact diagonalization and matrix product state methods, we map out the dynamical phase diagram of the PXP model with the quenched chemical potential. We demonstrate the existence of a continuous family of initial states that give rise to QMBS and formulate a ramping protocol that can be used to prepare such states in experiment. Our results show the ubiquity of scarring in the PXP model and highlight its intriguing interplay with quantum criticality.
Bumps, chimera states, and Turing patterns in systems of coupled active rotators
Franović, Igor; Omel'chenko, Oleh E.; Wolfrum, Matthias
Self-organized coherence-incoherence patterns, called chimera states, have first been reported in systems of Kuramoto oscillators. For coupled excitable units, similar patterns where coherent units are at rest are called bump states. Here, we study bumps in an array of active rotators coupled by nonlocal attraction and global repulsion. We demonstrate how they can emerge in a supercritical scenario from completely coherent Turing patterns: a single incoherent unit appears in a homoclinic bifurcation, undergoing subsequent transitions to quasiperiodic and chaotic behavior, which eventually transforms into extensive chaos with many incoherent units. We present different types of transitions and explain the formation of coherence-incoherence patterns according to the classical paradigm of short-range activation and long-range inhibition.
C and Fortran OpenMP programs for rotating Bose–Einstein condensates
Kishor Kumar, Ramavarmaraja; Lončar, Vladimir; Muruganandam, Paulsamy; Adhikari, Sadhan K.; Balaž, Antun
We present OpenMP versions of C and Fortran programs for solving the Gross–Pitaevskii equation for a rotating trapped Bose–Einstein condensate (BEC) in two (2D) and three (3D) spatial dimensions. The programs can be used to generate vortex lattices and study dynamics of rotating BECs. We use the split-step Crank–Nicolson algorithm for imaginary- and real-time propagation to calculate stationary states and BEC dynamics, respectively. The simulation input parameters for the C programs are provided via input files, while for the Fortran programs they are given at the beginning of each program and therefore their change requires recompilation of the corresponding program. The programs propagate the condensate wave function and calculate several relevant physical quantities, such as the energy, the chemical potential, and the root-mean-square sizes. The imaginary-time propagation starts with an analytic wave function with one vortex at the trap center, modulated by a random phase at different space points. Nevertheless, the converged wave function for a rapidly rotating BEC with a large number of vortices is most efficiently calculated using the pre-calculated converged wave function of a rotating BEC containing a smaller number of vortices as the initial state rather than using an analytic wave function with one vortex as the initial state. These pre-calculated initial states exhibit rapid convergence for fast-rotating condensates to states containing multiple vortices with an appropriate phase structure. This is illustrated here by calculating vortex lattices with up to 61 vortices in 2D and 3D. Outputs of the programs include calculated physical quantities, as well as the wave function and different density profiles (full density, integrated densities in lower dimensions, and density cross-sections). The provided real-time propagation programs can be used to study the dynamics of a rotating BEC using the imaginary-time stationary wave function as the initial state. We also study the efficiency of parallelization of the present OpenMP C and Fortran programs with different compilers. Program summary Program title: BEC-GP-ROT-OMP, consisting of: (1) BEC-GP-ROT-OMP-C package, containing programs (i) bec-gp-rot-2d-th and (ii) bec-gp-rot-3d-th; (2) BEC-GP-ROT-OMP-F package, containing programs (i) bec-gp-rot-2d-th and (ii) bec-gp-rot-3d-th. Program files doi: http://dx.doi.org/10.17632/cw7tkn22v2.2 Licensing provisions: Apache License 2.0 Programming language: OpenMP C; OpenMP Fortran. The C programs are tested with the GNU, Intel, PGI, Oracle, and Clang compiler, and the Fortran programs are tested with the GNU, Intel, PGI, and Oracle compiler. Nature of problem: The present Open Multi-Processing (OpenMP) C and Fortran programs solve the time-dependent nonlinear partial differential Gross–Pitaevskii (GP) equation for a trapped rotating Bose–Einstein condensate in two (2D) and three (3D) spatial dimensions in a fully anisotropic traps. Solution method: We employ the split-step Crank–Nicolson algorithm to discretize the time-dependent GP equation in space and time. The discretized equation is then solved by imaginary- or real-time propagation, employing adequately small space and time steps, to yield the solution of stationary and non-stationary problems, respectively.
Calculations of electron mobility in II-VI semiconductors
Vukmirović, Nenad
Electron mobility in the conduction band of II-VI semiconductors ZnSe, CdTe, ZnTe, and CdSe was studied. Temperature dependence of mobility was calculated using the methodology based on density functional theory calculations of the electronic states, phonon modes, and electron-phonon coupling constants, along with Fourier-Wannier procedure for interpolation to a dense grid in momentum space. The mobilities obtained from calculations within generalized gradient approximation of density functional theory overestimate the experimental mobility several times. The calculation that used improved electronic band structure and high-frequency dielectric constants obtained using a hybrid functional lead to a very good agreement with experimental mobilities for most of the materials studied. It was also found that the Frohlich model provides a reasonably good estimate of mobilities around room temperature where longitudinal optical phonons provide the dominant scattering mechanism, as expected for these direct gap materials where all relevant electronic states are in the vicinity of the Gamma point. The results indicate as well that the long-ranged part of electron-phonon interaction fully determines the electron mobility in the materials studied. For this reason, the approach where only this part of electron-phonon interaction is calculated using the relevant analytical formulas allows for accurate calculation of mobility without the use of the interpolation procedure for electron-phonon coupling constants.

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