Superconductivity at the Two-Dimensional Limit

Abstract

Superconductivity in the extreme two-dimensional limit is studied on ultrathin lead films down to two atomic layers, where only a single channel of quantum well states exists. Scanning tunneling spectroscopy reveals that local superconducting order remains robust until two atomic layers, where the transition temperature abruptly plunges to a lower value, depending sensitively on the exact atomic structure of the film. Our result shows that Cooper pairs can still form in the last two-dimensional channel of electron states, although their binding is strongly affected by the substrate.

Visualizing superconductivity in FeSe nanoflakes onSrTiO3by scanning tunneling microscopy

“…In order to study these phenomena, nanostructures with extremely small k F V are particularly interesting. Compared to conventional metal superconductors, [1][2][3][4][5][6][7][8]10 the layered superconducting compounds (e.g. cuprates and iron-based superconductors) generally exhibit a smaller k F and represent ideal systems to test the intriguing superconductivity in confined systems.…”

Negative Poisson’s ratios in metal nanoplates

“…By virtue of the enhancement of nanotechnology, numerous layered structures with a thickness of several atomic layers have been achieved for various applications, through experimental techniques such as atomic layer deposition, thermal evaporation, chemical vapour deposition and molecular beam epitaxy methods [47][48][49] . Therefore, a fundamental understanding of the elastic behaviour of nanoscale plate-shaped materials becomes more important.…”

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

“…More interestingly, the anisotropy of the m-band of a Pb film is smaller than for the band of the bulk, the reason for which needs more detailed studies. We can explain very strong thickness-dependent physical properties observed in Pb thin films [5][6][7][8][9][10][11][12][13][14][15][16][17] in terms of the 1-D-like DOS singularity developing from the 2-D band bending: it is simply because the electronic structure near EF is now dominated by the singularity. Although we have only studied 23 and 24 ML Pb films, we know where the VHS of other Pb films is from previous STS measurements [16].…”

“…This is the reason why the STS of Pb films display a series of peaks [10] like a 1-D system [29], which has not been observed in any other 2-D system. The QWSs around the Κ point do not show an evident relationship with the DOS because they always cross the Fermi level very steeply.…”

“…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]. These strong oscillations in the properties of thick Pb films are very puzzling since, according to theory, the quantum size effect should quickly become damped with increasing thickness [18].…”