Terahertz surface modes and electron-phonon coupling on 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Bi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Se</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>
(111)

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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“…Hence, the assignment and discussion about these features are beyond the scope of this work and will be treated separately. 55…”

Section: Resultsmentioning

confidence: 99%

Helium–Surface Interaction and Electronic Corrugation of Bi₂Se₃(111)

et al. 2019

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“… spin-echo (3HeSE) spectrometry, in particular, with its unprecedented resolution in the neV range, can in principle measure the ASP dispersion in the GHz domain. Recent HAS experiments have provided the dispersion curves of other THz electronic collective excitations such as phasons and amplitons occurring in charge density wave systems 60 , 61 and, with HeSE, in the long-period reconstructed surface 62 . As shown in the case of (111), bound-state resonance enhancement can be exploited in HAS experiments to amplify the response of low-energy electronic collective excitations 61 .…”

Section: Discussionmentioning

confidence: 99%

“…Recent HAS experiments have provided the dispersion curves of other THz electronic collective excitations such as phasons and amplitons occurring in charge density wave systems 60 , 61 and, with HeSE, in the long-period reconstructed surface 62 . As shown in the case of (111), bound-state resonance enhancement can be exploited in HAS experiments to amplify the response of low-energy electronic collective excitations 61 . On the other hand, fast neutral atom beams in grazing-incidence scattering experiments in the keV energy domain have also proved to have sufficient resolution to detect surface excitons in insulators 63 and plasmon coherent excitations at metal surfaces 64 : nothing prevents in principle their use at smaller incident energy and higher monochromaticity for ASP at metal surfaces.…”

Section: Discussionmentioning

confidence: 99%

Evidence for a spin acoustic surface plasmon from inelastic atom scattering

Benedek

Bernasconi

Campi

et al. 2021

Sci Rep

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Closed-shell atoms scattered from a metal surface exchange energy and momentum with surface phonons mostly via the interposed surface valence electrons, i.e., via the creation of virtual electron-hole pairs. The latter can then decay into surface phonons via electron-phonon interaction, as well as into acoustic surface plasmons (ASPs). While the first channel is the basis of the current inelastic atom scattering (IAS) surface-phonon spectroscopy, no attempt to observe ASPs with IAS has been made so far. In this study we provide evidence of ASP in Ni(111) with both Ne atom scattering and He atom scattering. While the former measurements confirm and extend so far unexplained data, the latter illustrate the coupling of ASP with phonons inside the surface-projected phonon continuum, leading to a substantial reduction of the ASP velocity and possibly to avoided crossing with the optical surface phonon branches. The analysis is substantiated by a self-consistent calculation of the surface response function to atom collisions and of the first-principle surface-phonon dynamics of Ni(111). It is shown that in Ni(111) ASP originate from the majority-spin Shockley surface state and are therefore collective oscillation of surface electrons with the same spin, i.e. it represents a new kind of collective quasiparticle: a Spin Acoustic Surface Plasmon (SASP).

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“…[151][152][153] Hence, HAS provides a sensitive probe to determine the surface phonon dispersion and energy dissipation processes in terms of the e-ph coupling constant, l, on the surfaces of these materials. The obtained experimental data of various TIs 92,145,[154][155][156][157][158][159] promise to evolve a more general picture about the surface dynamics and the atom-surface interaction of these peculiar surfaces. The e-ph 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 l. 145 Investigations of the archetypal TI which is Bi 2 Te 3 (111) 155 show a prominent surface acoustic mode that may have important implications in layered and nanoscale devices.…”

Section: Specific Science Cases For Combined Has/hese Investigationsmentioning

confidence: 95%