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Niggas A, Schwestka J, Balzer K, Weichselbaum D, Schlünzen N, Heller R, Creutzburg S, Inani H, Tripathi M, Speckmann C, McEvoy N, Susi T, Kotakoski J, Gan Z, George A, Turchanin A, Bonitz M, Aumayr F, Wilhelm RA. Ion-Induced Surface Charge Dynamics in Freestanding Monolayers of Graphene and MoS_{2} Probed by the Emission of Electrons. PHYSICAL REVIEW LETTERS 2022; 129:086802. [PMID: 36053690 DOI: 10.1103/physrevlett.129.086802] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 04/28/2022] [Accepted: 07/16/2022] [Indexed: 06/15/2023]
Abstract
We compare the ion-induced electron emission from freestanding monolayers of graphene and MoS_{2} to find a sixfold higher number of emitted electrons for graphene even though both materials have similar work functions. An effective single-band Hubbard model explains this finding by a charge-up in MoS_{2} that prevents low energy electrons from escaping the surface within a period of a few femtoseconds after ion impact. We support these results by measuring the electron energy distribution for correlated pairs of electrons and transmitted ions. The majority of emitted primary electrons have an energy below 10 eV and are therefore subject to the dynamic charge-up effects at surfaces.
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Affiliation(s)
- Anna Niggas
- TU Wien, Institute of Applied Physics, 1040 Vienna, Austria
| | | | - Karsten Balzer
- Computing Center of Kiel University, 24118 Kiel, Germany
| | | | - Niclas Schlünzen
- Kiel University, Institute for Theoretical Physics and Astrophysics, 24098 Kiel, Germany
| | - René Heller
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, 01328 Dresden, Germany
| | - Sascha Creutzburg
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, 01328 Dresden, Germany
| | - Heena Inani
- University of Vienna, Faculty of Physics, 1090 Vienna, Austria
| | - Mukesh Tripathi
- University of Vienna, Faculty of Physics, 1090 Vienna, Austria
| | - Carsten Speckmann
- University of Vienna, Faculty of Physics, 1090 Vienna, Austria
- University of Vienna, Vienna Doctoral School in Physics, 1090 Vienna, Austria
| | - Niall McEvoy
- Trinity College Dublin, Advanced Materials and Bioengineering Research Centre (AMBER) and School of Chemistry, College Green, Dublin 2, Ireland
| | - Toma Susi
- University of Vienna, Faculty of Physics, 1090 Vienna, Austria
| | - Jani Kotakoski
- University of Vienna, Faculty of Physics, 1090 Vienna, Austria
| | - Ziyang Gan
- Friedrich Schiller University Jena, Institute of Physical Chemistry, 07743 Jena, Germany
| | - Antony George
- Friedrich Schiller University Jena, Institute of Physical Chemistry, 07743 Jena, Germany
| | - Andrey Turchanin
- Friedrich Schiller University Jena, Institute of Physical Chemistry, 07743 Jena, Germany
| | - Michael Bonitz
- Kiel University, Institute for Theoretical Physics and Astrophysics, 24098 Kiel, Germany
- Kiel Nano, Surface and Interface Science KiNSIS, Kiel, Germany
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Moldabekov ZA, Dornheim T, Bonitz M, Ramazanov TS. Ion energy-loss characteristics and friction in a free-electron gas at warm dense matter and nonideal dense plasma conditions. Phys Rev E 2020; 101:053203. [PMID: 32575188 DOI: 10.1103/physreve.101.053203] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Accepted: 04/16/2020] [Indexed: 06/11/2023]
Abstract
We investigate the energy-loss characteristics of an ion in warm dense matter (WDM) and dense plasmas concentrating on the influence of electronic correlations. The basis for our analysis is a recently developed ab initio quantum Monte Carlo- (QMC) based machine learning representation of the static local field correction (LFC) [Dornheim et al., J. Chem. Phys. 151, 194104 (2019)JCPSA60021-960610.1063/1.5123013], which provides an accurate description of the dynamical density response function of the electron gas at the considered parameters. We focus on the polarization-induced stopping power due to free electrons, the friction function, and the straggling rate. In addition, we compute the friction coefficient which constitutes a key quantity for the adequate Langevin dynamics simulation of ions. Considering typical experimental WDM parameters with partially degenerate electrons, we find that the friction coefficient is of the order of γ/ω_{pi}=0.01, where ω_{pi} is the ionic plasma frequency. This analysis is performed by comparing QMC-based data to results from the random-phase approximation (RPA), the Mermin dielectric function, and the Singwi-Tosi-Land-Sjölander (STLS) approximation. It is revealed that the widely used relaxation time approximation (Mermin dielectric function) has severe limitations regarding the description of the energy loss of ions in a correlated partially degenerate electrons gas. Moreover, by comparing QMC-based data with the results obtained using STLS, we find that the ion energy-loss properties are not sensitive to the inaccuracy of the static local field correction (LFC) at large wave numbers, k/k_{F}>2 (with k_{F} being the Fermi wave number), but that a correct description of the static LFC at k/k_{F}≲1.5 is important.
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Affiliation(s)
- Zh A Moldabekov
- Institute for Experimental and Theoretical Physics, Al-Farabi Kazakh National University, 050040 Almaty, Kazakhstan
| | - T Dornheim
- Center for Advanced Systems Understanding (CASUS), Görlitz, Germany
| | - M Bonitz
- Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
| | - T S Ramazanov
- Institute for Experimental and Theoretical Physics, Al-Farabi Kazakh National University, 050040 Almaty, Kazakhstan
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Schlünzen N, Hermanns S, Scharnke M, Bonitz M. Ultrafast dynamics of strongly correlated fermions-nonequilibrium Green functions and selfenergy approximations. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:103001. [PMID: 31247604 DOI: 10.1088/1361-648x/ab2d32] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
This article presents an overview on recent progress in the theory of nonequilibrium Green functions (NEGF). We discuss applications of NEGF simulations to describe the femtosecond dynamics of various finite fermionic systems following an excitation out of equilibrium. This includes the expansion dynamics of ultracold atoms in optical lattices following a confinement quench and the excitation of strongly correlated electrons in a solid by the impact of a charged particle. NEGF, presently, are the only ab initio quantum approach that is able to study the dynamics of correlations for long times in two and three dimensions. However, until recently, NEGF simulations have mostly been performed with rather simple selfenergy approximations such as the second-order Born approximation (SOA). While they correctly capture the qualitative trends of the relaxation towards equilibrium, the reliability and accuracy of these NEGF simulations has remained open, for a long time. Here we report on recent tests of NEGF simulations for finite lattice systems against exact-diagonalization and density-matrix-renormalization-group benchmark data. The results confirm the high accuracy and predictive capability of NEGF simulations-provided selfenergies are used that go beyond the SOA and adequately include strong correlation and dynamical-screening effects. With an extended arsenal of selfenergies that can be used effectively, the NEGF approach has the potential of becoming a powerful simulation tool with broad areas of new applications including strongly correlated solids and ultracold atoms. The present review aims at making such applications possible. To this end we present a selfcontained introduction to the theory of NEGF and give an overview on recent numerical applications to compute the ultrafast relaxation dynamics of correlated fermions. In the second part we give a detailed introduction to selfenergies beyond the SOA. Important examples are the third-order approximation, the [Formula: see text] approximation, the T-matrix approximation and the fluctuating-exchange approximation. We give a comprehensive summary of the explicit selfenergy expressions for a variety of systems of practical relevance, starting from the most general expressions (general basis) and the Feynman diagrams, and including also the important cases of diagonal basis sets, the Hubbard model and the differences occuring for bosons and fermions. With these details, and information on the computational effort and scaling with the basis size and propagation duration, readers will be able to choose the proper basis set and straightforwardly implement and apply advanced selfenergy approximations to a broad class of systems.
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Affiliation(s)
- N Schlünzen
- Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany
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Schlünzen N, Joost JP, Bonitz M. Achieving the Scaling Limit for Nonequilibrium Green Functions Simulations. PHYSICAL REVIEW LETTERS 2020; 124:076601. [PMID: 32142347 DOI: 10.1103/physrevlett.124.076601] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Accepted: 12/24/2019] [Indexed: 06/10/2023]
Abstract
The dynamics of strongly correlated fermions following an external excitation reveals extremely rich collective quantum effects. Examples are fermionic atoms in optical lattices, electrons in correlated materials, and dense quantum plasmas. Presently, the only quantum-dynamics approach that rigorously describes these processes in two and three dimensions is the nonequilibrium Green functions (NEGF) method. However, NEGF simulations are computationally expensive due to their T^{3} scaling with the simulation duration T. Recently, T^{2} scaling was achieved with the generalized Kadanoff-Baym ansatz (GKBA), for second-order Born (SOA) selfenergies, which has substantially extended the scope of NEGF simulations. Here we demonstrate that GKBA-NEGF simulations can be performed with order T^{1} scaling, both for SOA and GW selfenergies, and point out the remarkable capabilities of this approach.
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Affiliation(s)
- Niclas Schlünzen
- Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany
| | - Jan-Philip Joost
- Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany
| | - Michael Bonitz
- Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany
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Joost JP, Jauho AP, Bonitz M. Correlated Topological States in Graphene Nanoribbon Heterostructures. NANO LETTERS 2019; 19:9045-9050. [PMID: 31735027 DOI: 10.1021/acs.nanolett.9b04075] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Finite graphene nanoribbon (GNR) heterostructures host intriguing topological in-gap states (Rizzo, D. J.; et al. Nature2018, 560, 204). These states may be localized either at the bulk edges or at the ends of the structure. Here we show that correlation effects (not included in previous density functional simulations) play a key role in these systems: they result in increased magnetic moments at the ribbon edges accompanied by a significant energy renormalization of the topological end states, even in the presence of a metallic substrate. Our computed results are in excellent agreement with the experiments. Furthermore, we discover a striking, novel mechanism that causes an energy splitting of the nonzero-energy topological end states for a weakly screened system. We predict that similar effects should be observable in other GNR heterostructures as well.
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Affiliation(s)
- Jan-Philip Joost
- Institut für Theoretische Physik und Astrophysik , Christian-Albrechts-Universität zu Kiel , D-24098 Kiel , Germany
| | - Antti-Pekka Jauho
- CNG, DTU Physics , Technical University of Denmark , Kongens Lyngby , DK 2800 , Denmark
| | - Michael Bonitz
- Institut für Theoretische Physik und Astrophysik , Christian-Albrechts-Universität zu Kiel , D-24098 Kiel , Germany
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