Superconductivity Modulated by Quantum Size Effects

Guo, Yang; Zhang, Yanfeng; Bao, Xinyu; Han, Tao; Tang, Zhe; Zhang, Lixin; Zhu, Wenguang; Wang, E. G.; Niu, Qian; Qiu, Z. Q.; Jia, Jin‐Feng; Zhao, Zhongxian; Xue, Qi‐Kun

doi:10.1126/science.1105130

Cited by 568 publications

(456 citation statements)

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“…[1][2][3][4] Perhaps, the best illustrated example of the QSE are Pb films on Si͑111͒, where various properties, such as the surface energy, the superconducting transition temperature, the interlayer spacing, and the film stability, oscillate with the film thickness. [5][6][7][8][9][10][11] The QSE also favors magic film thicknesses, corresponding to the electron energy minima at F / 2 intervals. [6][7][8]12,13 This drives metal thin films with unfavored thicknesses to stabilize by relaxing the interlayer spacing.…”

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confidence: 99%

Quantum size effect induced dilute atomic layers in ultrathin Al films

Jiang

Tang

et al. 2007

Phys. Rev. B

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We illustrate using scanning tunneling microscopy and low energy electron diffraction that thin Al films grown on Si͑111͒-ͱ 3 ϫ ͱ 3-Al substrates form layers having unusual thicknesses, not compatible with a normal fcc stacking of dense Al͑111͒-1 ϫ 1 layers ͑coverageϽ wetting layer+ 7 Å͒. This structure is shown to be based on inserted dilute 1.5ϫ 1.5 atomic layers. At a film thickness of the wetting layer+ 7 Å, the film undergoes a phase transformation and continues to grow in the normal stacking of Al͑111͒-1 ϫ 1 layers. The phenomenon is explained within the theory of the quantum size effects in a jellium metal combined with strain effects. We argue that the insertion of dilute atomic layers for small film thicknesses allows the Al film to reach thicknesses perfectly well adjusted to the minima of the oscillating electron energy, which arises from the spatial confinement of the free electrons in the thin film. In contrast, at larger thicknesses, where the electron energy differences diminish, a strain-driven phase transformation drives the system back to the classical close-packed Al͑111͒-1 ϫ 1 fcc stacking. The isotropic property of the metallic bonding drives metal ions to get as close as possible in order to maximize the overlap of the wave functions and to minimize the energy. Therefore, most metals form close-packed crystalline structures with high coordination numbers. Depending on the shape and extension of the wave functions involved, metals crystallize preferentially in the close-packed face-centered cubic or hexagonal structures or in the nearly close-packed body-centered cubic structure. In the conventional understanding, deviations from this principle should only occur if the bonds between the metal atoms become directional, i.e., exhibit covalent contributions. Here, we demonstrate, however, that a pure single element metal can also form a stack of dilute and dense close-packed atomic layers and thus deviate from the closed-packed principle in dimensionally reduced structures. The driving force is not a directional component of the metallic bond but rather a reduction of the electron energy governed by quantum size effects. Once the gain of electron energy vanishes with increasing film thickness, the whole system undergoes, however, a strain-driven phase transformation from alternating dilute and dense atomic layers to only close-packed layers.Quantum mechanics and thus also quantum size effects ͑QSEs͒ become relevant for spatially confined structures, such as thin metal films, whose thickness is comparable to the Fermi wavelength F . 1-4 Perhaps, the best illustrated example of the QSE are Pb films on Si͑111͒, where various properties, such as the surface energy, the superconducting transition temperature, the interlayer spacing, and the film stability, oscillate with the film thickness. [5][6][7][8][9][10][11] The QSE also favors magic film thicknesses, corresponding to the electron energy minima at F / 2 intervals. [6][7][8]12,13 This drives metal thin films with unfavored thicknesses to stabil...

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confidence: 99%

Quantum size effect induced dilute atomic layers in ultrathin Al films

Jiang

Tang

et al. 2007

Phys. Rev. B

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“…Quantized QWSs are clearly observed in STS, and these give rise to the high DOS in the films. We know that the bottoms of the m-shaped bands near the Γ point in the ARPES measurements correspond to the energy positions of the peaks in the normal emission experiment [5]. However, the high DOS regions (the peaks) in STS do not match the band bottoms but, rather, the tops where the m-shaped bands start bending to higher binding Fig.…”

Section: Resultsmentioning

confidence: 99%

“…In this regard, Pb thin films represent a peculiar system. In this system, quantum size effects have been observed to drive quantum oscillation of many properties with a period of 2 ML: examples include the superconducting transition temperature T c [5][6], thermal stability [11], thermal expansion coefficient [12], electron-phonon coupling [13], local work function [14], surface reactivity [15] and Kondo effect [16]. These have been explained by an oscillation in electronic density of states (DOS) near the Fermi level (E F ) [5][6][7][8][9][10][11][12][13][14][15][16][17], particularly in the bottom of subbands that pass though the Fermi level [18,19].…”

Section: Introductionmentioning

confidence: 99%

“…In this system, quantum size effects have been observed to drive quantum oscillation of many properties with a period of 2 ML: examples include the superconducting transition temperature T c [5][6], thermal stability [11], thermal expansion coefficient [12], electron-phonon coupling [13], local work function [14], surface reactivity [15] and Kondo effect [16]. These have been explained by an oscillation in electronic density of states (DOS) near the Fermi level (E F ) [5][6][7][8][9][10][11][12][13][14][15][16][17], particularly in the bottom of subbands that pass though the Fermi level [18,19]. More interestingly, the oscillations in the properties of Pb persist for large film thicknesses, and quantized electronic states have even been observed at film thicknesses up to 45 ML [14], a much larger thickness [5][6][7][8][9][10][11][12][13][14][15][16][17] than observed for other films [2][3][4].…”

Section: Introductionmentioning

confidence: 99%

“…The electronic structure of Pb films with different thicknesses has been studied by photoemission spectroscopy and scanning tunneling spectroscopy (STS) [5,12,[14][15][16]. Many of these studies have revealed that the oscillations in the DOS at E F are consistent with the observed properties of the films-for instance, higher superconducting transition temperature (T c ) [5], surface reactivity [15] and Kondo temperature [16]. However, why the Pb films exhibit much stronger DOS oscillations than other 2-D systems is still an open question.…”

Section: Introductionmentioning

confidence: 99%

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Van Hove singularities as a result of quantum confinement: The origin of intriguing physical properties in Pb thin films

Sun

Souma

et al. 2010

Nano Res.

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In situ angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS) have been used to study the electronic structure of Pb thin films grown on a Si (111) substrates. The experiments reveal that the electronic structure near the Fermi energy is dominated by a set of m-shaped subbands because of strong quantum confinement in the films, and the tops of the m-shaped subbands form an intriguing ring-like Van Hove singularity. Combined with theoretical calculations, we show that it is the Van Hove singularity that leads to an extremely high density of states near the Fermi energy and the recently reported strong oscillations (with a period of two monolayers) in various properties of Pb films.

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Scanning Probe Microscopy – From Surfaces to Single Atoms

Néel

2020

Digital Encyclopedia of Applied Physics

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This article highlights the important role of scanning tunneling and atomic force microscopy in modern surface science experiments. Imaging with atomic resolution, manipulation of matter atom by atom, spectroscopy of confined electrons, molecular vibrational quanta, surface phonons, single‐atom spin flips, and single‐molecule fluorescence photons are some of the diverse applications of the microscopes. The impact of the actual atomic or molecular termination of the tip is emphasized. A variety of examples presents the state of the art in quantum physics of surfaces and interfaces and demonstrates that scanning probe techniques significantly contribute to the understanding of matter at the atomic scale.

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Superconductivity Modulated by Quantum Size Effects

Cited by 568 publications

References 22 publications

Quantum size effect induced dilute atomic layers in ultrathin Al films

Quantum size effect induced dilute atomic layers in ultrathin Al films

Van Hove singularities as a result of quantum confinement: The origin of intriguing physical properties in Pb thin films

Scanning Probe Microscopy – From Surfaces to Single Atoms

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