Controlling conductivity by quantum well states in ultrathin Bi(111) films

Kröger, Philipp; Abdelbarey, D.; Siemens, Mark E.; Lükermann, Daniel; Sologub, S.V.; Pfnür, H.; Tegenkamp, Christoph

doi:10.1103/physrevb.97.045403

Cited by 23 publications

(24 citation statements)

References 28 publications

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“…The transport experiment in ref. (23) indeed detected a signature of surface states possessing finite contributions in the film interior. Nevertheless, the experiment succeeded in separating thickness-…”

Section: F the Distinction Between Surface And Bulk States In Atomicmentioning

confidence: 90%

Surface-state Coulomb repulsion accelerates a metal-insulator transition in topological semimetal nanofilms

et al. 2020

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The emergence of quantization at the nanoscale, the quantum size effect (QSE), allows flexible control of matter and is a rich source of advanced functionalities. A QSE-induced transition into an insulating phase in semimetallic nanofilms was predicted for bismuth a halfcentury ago and has regained new interest with regard to its surface states exhibiting nontrivial electronic topology. Here, we reveal an unexpected mechanism of the transition by high-resolution angle-resolved photoelectron spectroscopy combined with theoretical calculations. Anomalous evolution and degeneracy of quantized energy levels indicate that increased Coulomb repulsion from the surface states deforms a quantum confinement potential with decreasing thickness. The potential deformation strongly modulates spatial distributions of quantized wave functions, which leads to acceleration of the transition beyond the original QSE picture. This discovery establishes a complete picture of the long-discussed transition and highlights a new class of size effects dominating nanoscale transport in systems with metallic surface states. Teaser (127 characters)Increased Coulomb repulsion from surface states significantly modulates quantum confinement in topological semimetal nanofilms. 2 MAIN TEXT IntroductionQuantized electronic states generated by the quantum size effect (QSE) in nano-confined systems enable unique tunability for a wide range of phenomena such as superconductivity (1), light-matter interaction (2), and non-equilibrium carrier dynamics (3). Modulations of the band gap and the density of states further improve functionalities in catalysts (4) and information devices (5). From a technological point of view, quantization inevitably affects any electronic system fabricated at the nanoscale. One of the most well-known examples is a QSE-induced metal-insulator transition, whose essence is illustrated for a film geometry in Figs. 1 (A and B). When semimetallic bulk bands are quantized, the valence-band top and the conduction-band bottom no longer cross the Fermi level ( ), and the system enters an insulating phase. In the case of a system possessing metallic surface states as typically observed in topological materials, the transition is marked by the disappearance of conducting channels in the film interior, and thereafter electric current flows only through the surfaces. The transition was first predicted a half-century ago on bismuth (Bi) (6). A Bi single crystal is a typical semimetal with small carrier pockets and three-dimensional (3D) Dirac dispersions (7), which generate unusual magneto-transport responses (8-10). Moreover, due to the large spin-orbit coupling, Bi surfaces host spin-polarized metallic states (Figs. 1, A, B, and E) that have been intensively examined in the context of electronic topology (11-16). Although theoretical calculations tended to predict trivial band topology (11, 12), angle-resolved photoelectron spectroscopy (ARPES) experiments have detected electronic band structures exhibiting nontrivial topology (13,14). A...

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Section: F the Distinction Between Surface And Bulk States In Atomicmentioning

confidence: 90%

Surface-state Coulomb repulsion accelerates a metal-insulator transition in topological semimetal nanofilms

et al. 2020

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“…In this section, we concentrate on the interpretation of experimental results for Bismuth films from the literature. The experimental results of Kröger et al [4] and Hirahara et al [5], i.e. the energy level spacings ∆ E as a function of the Bi film thickness d, are depicted in Fig.…”

Section: Comparison With Experimentsmentioning

confidence: 97%

“…Kröger, measurement 1 Kröger, measurement 2 Kröger, measurement 3 Hirahara Theory fit Fig. 1 Experimental data of Kröger et al [4] (3 different Bi films) and Hirahara et al [5] in comparison with a fit to the harmonic oscillator.…”

Section: ∆E [Ev]mentioning

confidence: 99%

“…For epitaxially grown SnO 2 , InSb, and Pb films with low charge densities, measurements with exponents about 1.5 have been reported [1][2][3]. Furthermore, Kröger et al [4] and Hirahara et al [5] investigated Bi films [6][7][8][9][10] and demonstrated that these exhibit equidistant energy levels with a 1/d thickness dependence [4,5]. For this, Kröger et al prepared epitaxially grown Bi(111) films on Si(111) samples.…”

Section: Introductionmentioning

confidence: 99%

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Do Equidistant Energy Levels Necessitate a Harmonic Potential?

Teichert

Kühn

Thränhardt

2021

Preprint

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Experimental results from literature show equidistant energy levels in thin Bi films on surfaces, suggesting a harmonic oscillator description. Yet this conclusion is by no means imperative, especially considering that any measurement only yields energy levels in a finite range and with a nonzero uncertainty. Within this study we review isospectral potentials from the literature and investigate the applicability of the harmonic oscillator hypothesis to recent measurements. First, we describe experimental results from literature by a harmonic oscillator model, obtaining a realistic size and depth of the resulting quantum well. Second, we use the shift-operator approach to calculate anharmonic non-polynomial potentials producing (partly) equidistant spectra. We discuss different potential types and interpret the possible modeling applications. Finally, by applying n th o rder perturbation theory we show that exactly equidistant eigenenergies cannot be achieved by polynomial potentials, except by the harmonic oscillator potential. In summary, we aim to give an overview over which conclusions may be drawn from the experimental determination of energy levels and which may not.

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“…Semiconductor-like behavior was confirmed by measurements of the temperature dependent conductivity, e.g., in Refs. [4][5][6][7][8][9]. The expected quantum confinement relies on the assumption that the crystal structure in the nanoscale system does not change considerably compared to the bulk and that there are no conducting surface states.…”

Section: Introductionmentioning

confidence: 99%

Structural modification of thin Bi(1 1 1) films by passivation and native oxide model

König

Fahy

Greer

2019

Phys. Rev. Materials

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The structure of thin terminated Bi(1 1 1) films of approximately 1 nm thickness is investigated from first principles. Our density functional theory calculations show that covalent bonds to the surface can change the orientation of the films completely. For thicker films, the effect is limited to the surface only. Based on these observations, we further present a simple model structure for the native oxide and chemically similar oxides, which form a protective capping layer, leaving the orientation of the films unchanged. The advantages of this energetically favorable layered termination are discussed in the context of the films' technological exploitation in nanoelectronic devices. arXiv:1903.12654v2 [cond-mat.mtrl-sci]

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Controlling conductivity by quantum well states in ultrathin Bi(111) films

Cited by 23 publications

References 28 publications

Surface-state Coulomb repulsion accelerates a metal-insulator transition in topological semimetal nanofilms

Surface-state Coulomb repulsion accelerates a metal-insulator transition in topological semimetal nanofilms

Do Equidistant Energy Levels Necessitate a Harmonic Potential?

Structural modification of thin Bi(1 1 1) films by passivation and native oxide model

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