1
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Ruckhofer A, Benedek G, Bremholm M, Ernst WE, Tamtögl A. Observation of Dirac Charge-Density Waves in Bi 2Te 2Se. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:476. [PMID: 36770437 PMCID: PMC9919891 DOI: 10.3390/nano13030476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 01/18/2023] [Accepted: 01/19/2023] [Indexed: 06/18/2023]
Abstract
While parallel segments in the Fermi level contours, often found at the surfaces of topological insulators (TIs), would imply "strong" nesting conditions, the existence of charge-density waves (CDWs)-periodic modulations of the electron density-has not been verified up to now. Here, we report the observation of a CDW at the surface of the TI Bi2Te2Se(111), below ≈350K, by helium-atom scattering and, thus, experimental evidence for a CDW involving Dirac topological electrons. Deviations of the order parameter observed below 180K, and a low-temperature break of time reversal symmetry, suggest the onset of a spin-density wave with the same period as the CDW in the presence of a prominent electron-phonon interaction, originating from Rashba spin-orbit coupling.
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Affiliation(s)
- Adrian Ruckhofer
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
| | - Giorgio Benedek
- Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
- Donostia International Physics Center, University of the Basque Country, Paseo M. de Lardizabal 4, 20018 Donostia/San Sebastián, Spain
| | - Martin Bremholm
- Centre for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, 8000 Aarhus, Denmark
| | - Wolfgang E. Ernst
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
| | - Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
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2
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Sacchi M, Tamtögl A. Water adsorption and dynamics on graphene and other 2D materials: Computational and experimental advances. ADVANCES IN PHYSICS: X 2022; 8:2134051. [PMID: 36816858 PMCID: PMC7614201 DOI: 10.1080/23746149.2022.2134051] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 09/26/2022] [Accepted: 09/27/2022] [Indexed: 06/18/2023] Open
Abstract
The interaction of water and surfaces, at molecular level, is of critical importance for understanding processes such as corrosion, friction, catalysis and mass transport. The significant literature on interactions with single crystal metal surfaces should not obscure unknowns in the unique behaviour of ice and the complex relationships between adsorption, diffusion and long-range inter-molecular interactions. Even less is known about the atomic-scale behaviour of water on novel, non-metallic interfaces, in particular on graphene and other 2D materials. In this manuscript, we review recent progress in the characterisation of water adsorption on 2D materials, with a focus on the nano-material graphene and graphitic nanostructures; materials which are of paramount importance for separation technologies, electrochemistry and catalysis, to name a few. The adsorption of water on graphene has also become one of the benchmark systems for modern computational methods, in particular dispersion-corrected density functional theory (DFT). We then review recent experimental and theoretical advances in studying the single-molecular motion of water at surfaces, with a special emphasis on scattering approaches as they allow an unparalleled window of observation to water surface motion, including diffusion, vibration and self-assembly.
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Affiliation(s)
- M. Sacchi
- Department of Chemistry, University of Surrey, Guildford GU2 7XH, UK
| | - A. Tamtögl
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria
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3
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Chadwick H, Cantin JT, Alkoby Y, Alexandrowicz G. Multiple echoes in beam spin-echo spectroscopy and their effect on measurements of ultra-fast dynamics. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:345901. [PMID: 35679846 DOI: 10.1088/1361-648x/ac7765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 06/09/2022] [Indexed: 06/15/2023]
Abstract
Helium (3He) spin-echo is a powerful experimental technique used to probe ultra-fast atomic scale surface dynamics. The analysis of these measurements is typically performed assuming there is only a single spin-echo condition, expected to produce a constant signal for pure elastic scattering, a monotonically decaying signal for quasi-elastic scattering and oscillations from inelastic scattering events. In the present work, we show that there are in fact four spin-echoes which must be correctly accounted for, and that even in the case of elastic scattering these additional echoes lead to oscillations which could mistakenly be interpreted as being due to inelastic scattering. We demonstrate that it is possible to accurately simulate the experimental data by propagating the3He through the measured magnetic field profile of the apparatus and considering the geometry of the machine, allowing the effect of these additional echoes to be disentangled from inelastic scattering events in future3He spin-echo measurements.
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Affiliation(s)
- Helen Chadwick
- Department of Chemistry, Faculty of Science and Engineering, Swansea University, Swansea SA2 8PP, United Kingdom
| | - Joshua T Cantin
- Department of Chemistry, Faculty of Science and Engineering, Swansea University, Swansea SA2 8PP, United Kingdom
| | - Yosef Alkoby
- Department of Chemistry, Faculty of Science and Engineering, Swansea University, Swansea SA2 8PP, United Kingdom
| | - Gil Alexandrowicz
- Department of Chemistry, Faculty of Science and Engineering, Swansea University, Swansea SA2 8PP, United Kingdom
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4
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Ghim M, Jhi SH. Kohn anomalies in topological insulator thin films: first-principles study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:265002. [PMID: 35405670 DOI: 10.1088/1361-648x/ac664a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Accepted: 04/11/2022] [Indexed: 06/14/2023]
Abstract
Kohn anomaly is a non-smooth phonon softening induced by electron-phonon coupling in low-dimensional metals. Some measurements claimed that Kohn anomalies are present in topological materials due to the Dirac fermions in the bulk or in the surface. However, first-principles calculations have not reproduced the Kohn anomalies, especially, on the surface of topological insulators. It is still unclear about the origin of the controversy for the existence of the Kohn anomaly whether it is a numerical shortcoming or misinterpretation in measurement. In this study, we investigate the surface Kohn anomaly in two topological insulators Bi2Se3and SnSe using the state-of-the-art Wannier interpolation schemes. We find that Bi2Se3exhibits the Kohn anomaly but only in the bulk-like phonon modes by structural confinement along thec-axis. Interestingly, SnSe exhibits the surface Kohn anomaly in support of the experimental report on Pb0.7Sn0.3Se. We show that double Dirac cones in SnSe surface states are responsible for the Kohn anomaly, which is even enhanced if the subsurface states are partially occupied.
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Affiliation(s)
- Minjae Ghim
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
| | - Seung-Hoon Jhi
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
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5
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Eder SD, Hellner SK, Forti S, Nordbotten JM, Manson JR, Coletti C, Holst B. Temperature-Dependent Bending Rigidity of AB-Stacked Bilayer Graphene. PHYSICAL REVIEW LETTERS 2021; 127:266102. [PMID: 35029489 DOI: 10.1103/physrevlett.127.266102] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 10/28/2021] [Indexed: 06/14/2023]
Abstract
The change in bending rigidity with temperature κ(T) for 2D materials is highly debated: theoretical works predict both increase and decrease. Here we present measurements of κ(T), for a 2D material: AB-stacked bilayer graphene. We obtain κ(T) from phonon dispersion curves measured with helium atom scattering in the temperature range 320-400 K. We find that the bending rigidity increases with temperature. Assuming a linear dependence over the measured temperature region we obtain κ(T)=[(1.3±0.1)+(0.006±0.001)T/K] eV by fitting the data. We discuss this result in the context of existing predictions and room temperature measurements.
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Affiliation(s)
- S D Eder
- Department of Physics and Technology, University of Bergen, Allégaten 55, 5007 Bergen, Norway
| | - S K Hellner
- Department of Physics and Technology, University of Bergen, Allégaten 55, 5007 Bergen, Norway
| | - S Forti
- Center for Nanotechnology Innovation@NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
| | - J M Nordbotten
- Department of Mathematics, University of Bergen, Allégaten 41, 5007 Bergen, Norway
| | - J R Manson
- Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634, USA
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal, 4, 20018 Donostia-San Sebastián, Spain
| | - C Coletti
- Center for Nanotechnology Innovation@NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
| | - B Holst
- Department of Physics and Technology, University of Bergen, Allégaten 55, 5007 Bergen, Norway
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6
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Ruckhofer A, Halbritter S, Lund HE, Holt AJU, Bianchi M, Bremholm M, Benedek G, Hofmann P, Ernst WE, Tamtögl A. Inelastic helium atom scattering from Sb 2Te 3(111): phonon dispersion, focusing effects and surfing. Phys Chem Chem Phys 2021; 23:7806-7813. [PMID: 33136112 DOI: 10.1039/d0cp04738d] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
We present an experimental study of inelastic scattering processes on the (111) surface of the topological insulator Sb2Te3 using helium atom scattering. In contrast to other binary topological insulators such as Bi2Se3 and Bi2Te3, Sb2Te3 is much less studied and the as-grown Sb2Te3 sample turns out to be p-doped, with the Fermi-level located below the Dirac-point as confirmed by angle-resolved photoemission spectroscopy. We report the surface phonon dispersion along both high symmetry directions in the energy region below 11 meV, where the Rayleigh mode exhibits the strongest intensity. The experimental data is compared with a study based on density functional perturbation theory calculations, providing good agreement except for a set of additional peculiar inelastic events below the Rayleigh mode. In addition, an analysis of angular scans with respect to a number of additional inelastic events is presented, including resonance enhancement, kinematical focusing, focused inelastic resonance and surfing. In the latter case, phonon-assisted adsorption of the incident helium atom gives rise to a bound state where the helium atom rides the created Rayleigh wave.
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Affiliation(s)
- Adrian Ruckhofer
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria.
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7
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Tamtögl A, Ruckhofer A, Campi D, Allison W, Ernst WE. Atom-surface van der Waals potentials of topological insulators and semimetals from scattering measurements. Phys Chem Chem Phys 2021; 23:7637-7652. [PMID: 33492313 DOI: 10.1039/d0cp05388k] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The phenomenology of resonant scattering has been known since the earliest experiments upon scattering of atomic beams from surfaces and is a means of obtaining experimental information about the fundamentals of weak adsorption systems in the van der Waals regime. We provide an overview of the experimental approach based on new experimental data for the He-Sb2Te3(111) system, followed by a comparative overview and perspective of recent results for topological semimetal and insulator surfaces. Moreover, we shortly discuss the perspectives of calculating helium-surface interaction potentials from ab initio calculations. Our perspective demonstrates that atom-surface scattering provides direct experimental information about the atom-surface interaction in the weak physisorption regime and can also be used to determine the lifetime and mean free path of the trapped atom. We further discuss the effects of elastic and inelastic scattering on the linewidth and lifetime of the trapped He atom with an outlook on future developments and applications.
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Affiliation(s)
- Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria.
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8
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Ward DJ, Raghavan A, Tamtögl A, Jardine AP, Bahn E, Ellis J, Miret-Artès S, Allison W. Inter-adsorbate forces and coherent scattering in helium spin-echo experiments. Phys Chem Chem Phys 2021; 23:7799-7805. [PMID: 33331836 DOI: 10.1039/d0cp04539j] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In studies of dynamical systems, helium atoms scatter coherently from an ensemble of adsorbates as they diffuse on the surface. The results give information on the co-operative behaviour of interacting adsorbates and thus include the effects of both adsorbate-substrate and adsorbate-adsorbate interactions. Here, we discuss a method to disentangle the effects of interactions between adsorbates from those with the substrate. The result gives an approximation to observations that would be obtained if the scattering was incoherent. Information from the experiment can therefore be used to distinguish more clearly between long-range inter-adsorbate forces and the short range effects arising from the local lattice potential and associated thermal excitations. The method is discussed in the context of a system with strong inter-adsorbate interactions, sodium atoms diffusing on a copper (111) surface.
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Affiliation(s)
- David J Ward
- Cavendish Laboratory, J.J. Thomson Ave., Cambridge, CB3 0HE, UK.
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9
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Holst B, Alexandrowicz G, Avidor N, Benedek G, Bracco G, Ernst WE, Farías D, Jardine AP, Lefmann K, Manson JR, Marquardt R, Artés SM, Sibener SJ, Wells JW, Tamtögl A, Allison W. Material properties particularly suited to be measured with helium scattering: selected examples from 2D materials, van der Waals heterostructures, glassy materials, catalytic substrates, topological insulators and superconducting radio frequency materials. Phys Chem Chem Phys 2021; 23:7653-7672. [PMID: 33625410 DOI: 10.1039/d0cp05833e] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Helium Atom Scattering (HAS) and Helium Spin-Echo scattering (HeSE), together helium scattering, are well established, but non-commercial surface science techniques. They are characterised by the beam inertness and very low beam energy (<0.1 eV) which allows essentially all materials and adsorbates, including fragile and/or insulating materials and light adsorbates such as hydrogen to be investigated on the atomic scale. At present there only exist an estimated less than 15 helium and helium spin-echo scattering instruments in total, spread across the world. This means that up till now the techniques have not been readily available for a broad scientific community. Efforts are ongoing to change this by establishing a central helium scattering facility, possibly in connection with a neutron or synchrotron facility. In this context it is important to clarify what information can be obtained from helium scattering that cannot be obtained with other surface science techniques. Here we present a non-exclusive overview of a range of material properties particularly suited to be measured with helium scattering: (i) high precision, direct measurements of bending rigidity and substrate coupling strength of a range of 2D materials and van der Waals heterostructures as a function of temperature, (ii) direct measurements of the electron-phonon coupling constant λ exclusively in the low energy range (<0.1 eV, tuneable) for 2D materials and van der Waals heterostructures (iii) direct measurements of the surface boson peak in glassy materials, (iv) aspects of polymer chain surface dynamics under nano-confinement (v) certain aspects of nanoscale surface topography, (vi) central properties of surface dynamics and surface diffusion of adsorbates (HeSE) and (vii) two specific science case examples - topological insulators and superconducting radio frequency materials, illustrating how combined HAS and HeSE are necessary to understand the properties of quantum materials. The paper finishes with (viii) examples of molecular surface scattering experiments and other atom surface scattering experiments which can be performed using HAS and HeSE instruments.
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Affiliation(s)
- Bodil Holst
- Department of Physics and Technology, University of Bergen, Allegaten 55, 5007 Bergen, Norway.
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10
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Measuring the Electron–Phonon Interaction in Two-Dimensional Superconductors with He-Atom Scattering. CONDENSED MATTER 2020. [DOI: 10.3390/condmat5040079] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Helium-atom scattering (HAS) spectroscopy from conducting surfaces has been shown to provide direct information on the electron–phonon interaction, more specifically the mass-enhancement factor λ from the temperature dependence of the Debye–Waller exponent, and the mode-selected electron–phonon coupling constants λQν from the inelastic HAS intensities from individual surface phonons. The recent applications of the method to superconducting ultra-thin films, quasi-1D high-index surfaces, and layered transition-metal and topological pnictogen chalcogenides are briefly reviewed.
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11
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Benedek G, Miret-Artés S, Manson JR, Ruckhofer A, Ernst WE, Tamtögl A. Origin of the Electron-Phonon Interaction of Topological Semimetal Surfaces Measured with Helium Atom Scattering. J Phys Chem Lett 2020; 11:1927-1933. [PMID: 32032492 PMCID: PMC7061329 DOI: 10.1021/acs.jpclett.9b03829] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 02/07/2020] [Indexed: 06/10/2023]
Abstract
He atom scattering has been demonstrated to be a sensitive probe of the electron-phonon interaction parameter λ at metal and metal-overlayer surfaces. Here it is shown that the theory linking λ to the thermal attenuation of atom scattering spectra (the Debye-Waller factor) can be applied to topological semimetal surfaces, such as the quasi-one-dimensional charge-density-wave system Bi(114) and the layered pnictogen chalcogenides. The electron-phonon coupling, as determined for several topological insulators belonging to the class of bismuth chalcogenides, suggests a dominant contribution of the surface quantum well states over the Dirac electrons in terms of λ.
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Affiliation(s)
- Giorgio Benedek
- Donostia
International Physics Center (DIPC), Paseo Manuel de Lardizabal, 4, 20018 Donostia-San Sebastian, Spain
- Dipartimento
di Scienza dei Materiali, Università
di Milano-Bicocca, Via Cozzi 53, 20125 Milano, Italy
| | - Salvador Miret-Artés
- Donostia
International Physics Center (DIPC), Paseo Manuel de Lardizabal, 4, 20018 Donostia-San Sebastian, Spain
- Instituto
de Física Fundamental, Consejo Superior
de Investigaciones Científicas, Serrano 123, 28006 Madrid, Spain
| | - J. R. Manson
- Donostia
International Physics Center (DIPC), Paseo Manuel de Lardizabal, 4, 20018 Donostia-San Sebastian, Spain
- Department
of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634, United States
| | - Adrian Ruckhofer
- Institute
of Experimental Physics, Graz University
of Technology, 8010 Graz, Austria
| | - Wolfgang E. Ernst
- Institute
of Experimental Physics, Graz University
of Technology, 8010 Graz, Austria
| | - Anton Tamtögl
- Institute
of Experimental Physics, Graz University
of Technology, 8010 Graz, Austria
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12
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Tamtögl A, Sacchi M, Avidor N, Calvo-Almazán I, Townsend PSM, Bremholm M, Hofmann P, Ellis J, Allison W. Nanoscopic diffusion of water on a topological insulator. Nat Commun 2020; 11:278. [PMID: 31937778 PMCID: PMC6959239 DOI: 10.1038/s41467-019-14064-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 12/13/2019] [Indexed: 11/12/2022] Open
Abstract
The microscopic motion of water is a central question, but gaining experimental information about the interfacial dynamics of water in fields such as catalysis, biophysics and nanotribology is challenging due to its ultrafast motion, and the complex interplay of inter-molecular and molecule-surface interactions. Here we present an experimental and computational study of the nanoscale-nanosecond motion of water at the surface of a topological insulator (TI), Bi[Formula: see text]Te[Formula: see text]. Understanding the chemistry and motion of molecules on TI surfaces, while considered a key to design and manufacturing for future applications, has hitherto been hardly addressed experimentally. By combining helium spin-echo spectroscopy and density functional theory calculations, we are able to obtain a general insight into the diffusion of water on Bi[Formula: see text]Te[Formula: see text]. Instead of Brownian motion, we find an activated jump diffusion mechanism. Signatures of correlated motion suggest unusual repulsive interactions between the water molecules. From the lineshape broadening we determine the diffusion coefficient, the diffusion energy and the pre-exponential factor.
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Affiliation(s)
- Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, 8010, Graz, Austria.
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK.
| | - Marco Sacchi
- Department of Chemistry, University of Surrey, Guildford, GU2 7XH, UK
| | - Nadav Avidor
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
| | - Irene Calvo-Almazán
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
- Material Science Division, Argonne National Laboratory, Argonne, 60439, IL, USA
| | - Peter S M Townsend
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
- Department of Chemistry and Chemical Biology, Rutgers University, 123 Bevier Road, Piscataway, NJ, 08854, USA
| | - Martin Bremholm
- Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, 8000, Aarhus, Denmark
| | - Philip Hofmann
- Department of Physics and Astronomy, Interdisciplinary Nanoscience Center (iNANO), Aarhus University, 8000, Aarhus C, Denmark
| | - John Ellis
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
| | - William Allison
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
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13
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Zhang TT, Miao H, Wang Q, Lin JQ, Cao Y, Fabbris G, Said AH, Liu X, Lei HC, Fang Z, Weng HM, Dean MPM. Phononic Helical Nodal Lines with PT Protection in MoB_{2}. PHYSICAL REVIEW LETTERS 2019; 123:245302. [PMID: 31922848 DOI: 10.1103/physrevlett.123.245302] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Indexed: 06/10/2023]
Abstract
While condensed matter systems host both fermionic and bosonic quasiparticles, reliably predicting and empirically verifying topological states is only mature for Fermionic electronic structures, leaving topological Bosonic excitations sporadically explored. This is unfortunate, as Bosonic systems such as phonons offer the opportunity to assess spinless band structures where nodal lines can be realized without invoking special additional symetries to protect against spin-orbit coupling. Here we combine first-principles calculations and meV-resolution inelastic x-ray scattering to demonstrate the first realization of parity-time reversal symmetry protected helical nodal lines in the phonon spectrum of MoB_{2}. This structure is unique to phononic systems as the spin-orbit coupling present in electronic systems tends to lift the degeneracy away from high-symmetry locations. Our study establishes a protocol to accurately identify topological Bosonic excitations, opening a new route to explore exotic topological states in crystalline materials.
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Affiliation(s)
- T T Zhang
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
- Department of Physics, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8551, Japan
- Tokodai Institute for Element Strategy, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8503, Japan
| | - H Miao
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Q Wang
- Department of Physics and Beijing Key Laboratory of Opto-Electronic Functional Materials and Micro-devices, Renmin University of China, Beijing, China
| | - J Q Lin
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Y Cao
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - G Fabbris
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - A H Said
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - X Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - H C Lei
- Department of Physics and Beijing Key Laboratory of Opto-Electronic Functional Materials and Micro-devices, Renmin University of China, Beijing, China
| | - Z Fang
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - H M Weng
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - M P M Dean
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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14
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Ruckhofer A, Tamtögl A, Pusterhofer M, Bremholm M, Ernst WE. Helium-Surface Interaction and Electronic Corrugation of Bi 2Se 3(111). THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2019; 123:17829-17841. [PMID: 31608131 PMCID: PMC6781485 DOI: 10.1021/acs.jpcc.9b03450] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 06/13/2019] [Indexed: 06/10/2023]
Abstract
We present a study of the atom-surface interaction potential for the He-Bi2Se3(111) system. Using selective adsorption resonances, we are able to obtain the complete experimental band structure of atoms in the corrugated surface potential of the topological insulator Bi2Se3. He atom scattering spectra show several selective adsorption resonance features that are analyzed, starting with the free-atom approximation and a laterally averaged atom-surface interaction potential. Based on quantum mechanical calculations of the He-surface scattering intensities and resonance processes, we are then considering the three-dimensional atom-surface interaction potential, which is further refined to reproduce the experimental data. Following this analysis, the He-Bi2Se3(111) interaction potential is best represented by a corrugated Morse potential with a well depth of D = (6.54 ± 0.05) meV, a stiffness of κ = (0.58 ± 0.02) Å-1, and a surface electronic corrugation of (5.8 ± 0.2)% of the lattice constant. The experimental data may also be used as a challenging benchmark system to analyze the suitability of several van der Waals approaches: the He-Bi2Se3(111) interaction captures the fundamentals of weak adsorption systems where the binding is governed by long-range electronic correlations.
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Affiliation(s)
- Adrian Ruckhofer
- Institute
of Experimental Physics, Graz University
of Technology, Graz 8010, Austria
| | - Anton Tamtögl
- Institute
of Experimental Physics, Graz University
of Technology, Graz 8010, Austria
| | - Michael Pusterhofer
- Institute
of Experimental Physics, Graz University
of Technology, Graz 8010, Austria
| | - Martin Bremholm
- Centre
for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Aarhus 8000, Denmark
| | - Wolfgang E. Ernst
- Institute
of Experimental Physics, Graz University
of Technology, Graz 8010, Austria
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15
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Kalish S, Chamon C, El-Batanouny M, Santos LH, Sankar R, Chou FC. Contrasting the Surface Phonon Dispersion of Pb_{0.7}Sn_{0.3}Se in Its Topologically Trivial and Nontrivial Phases. PHYSICAL REVIEW LETTERS 2019; 122:116101. [PMID: 30951360 DOI: 10.1103/physrevlett.122.116101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2018] [Revised: 02/19/2019] [Indexed: 06/09/2023]
Abstract
We report inelastic He atom scattering measurements of the (001) surface phonon dispersion of the topological crystalline insulator Pb_{0.7}Sn_{0.3}Se. This material exhibits a temperature-dependent topological transition, so we measure the surface dispersion curves in both the trivial and nontrivial phases. We identify that, peculiarly, most surface modes are resonances, rather than pure surface states. We find that a shear vertical surface resonance branch around 9.0 meV dramatically changes on going from the trivial to the topological phase. We associate this remarkable change with the emergence of surface Dirac fermions. We use the measured dispersion of this resonance branch to determine the corresponding mode-dependent electron-phonon coupling λ_{ν}(q).
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Affiliation(s)
- S Kalish
- Department of Physics, Boston University, Boston, Massachusetts 02215, USA
| | - C Chamon
- Department of Physics, Boston University, Boston, Massachusetts 02215, USA
| | - M El-Batanouny
- Department of Physics, Boston University, Boston, Massachusetts 02215, USA
| | - L H Santos
- Institute for Condensed Theory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA and Department of Physics, Emory University, Atlanta, Georgia 30322, USA
| | - R Sankar
- Center of Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
| | - F C Chou
- Center of Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
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16
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Mal P, Bera G, Turpu GR, Srivastava SK, Gangan A, Chakraborty B, Das B, Das P. Vibrational spectra of Pb2Bi2Te3, PbBi2Te4, and PbBi4Te7 topological insulators: temperature-dependent Raman and theoretical insights from DFT simulations. Phys Chem Chem Phys 2019; 21:15030-15039. [DOI: 10.1039/c9cp01494b] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Insertion of lead and lead telluride in Bi2Te3 leads to a change in the thermal conductivity, frequency shift, and the broadening of phonon modes.
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Affiliation(s)
- Priyanath Mal
- Department of Pure and Applied Physics
- Guru Ghasidas Vishwavidyalaya
- Bilaspur-495009
- India
| | - G. Bera
- Department of Pure and Applied Physics
- Guru Ghasidas Vishwavidyalaya
- Bilaspur-495009
- India
| | - G. R. Turpu
- Department of Pure and Applied Physics
- Guru Ghasidas Vishwavidyalaya
- Bilaspur-495009
- India
| | - Sunil K. Srivastava
- Department of Physics
- Mahatma Gandhi Central University
- East Champaran
- Bihar-845401
- India
| | - A. Gangan
- High Pressure and Synchrotron Radiation Physics Division
- Bhabha Atomic Research Centre
- Mumbai-40008
- India
| | - Brahmananda Chakraborty
- High Pressure and Synchrotron Radiation Physics Division
- Bhabha Atomic Research Centre
- Mumbai-40008
- India
| | - Bipul Das
- Department of Physics
- National Changhua University of Education
- Changhua 500
- Taiwan
| | - Pradip Das
- Department of Pure and Applied Physics
- Guru Ghasidas Vishwavidyalaya
- Bilaspur-495009
- India
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