Imaging Josephson Vortices on the Surface SuperconductorSi(111)−(7×3)

Abstract

We have studied the superconducting Si(111)-( √ 7 × √ 3)-In surface using a 3 He-based lowtemperature scanning tunneling microscope (STM). Zero-bias conductance (ZBC) images taken over a large surface area reveal that vortices are trapped at atomic steps after magnetic fields are applied. The crossover behavior from Pearl to Josephson vortices is clearly identified from their elongated shapes along the steps and significant recovery of superconductivity within the cores. Our numerical calculations combined with experiments clarify that these characteristic features are determined by the relative strength of the interterrace Josephson coupling at the atomic step.PACS numbers: 74.25. Ha,74.55.+v,74.50.+r The recent discovery of superconductivity in silicon surface reconstructions with metal adatoms was an unexpected surprise, because they are regarded as one of the thinnest two-dimensional (2D) materials ever possible [1][2][3][4][5]. This class of surface 2D materials has now become relevant for extensive superconductor researches in progress [6][7][8][9]. Notably, these new studies have been advanced by surface analytical techniques such as scanning tunneling microscopy (STM) [1,5,7,8] and ultrahigh vacuum (UHV)-compatible transport measurement [2-4, 10, 11].One ubiquitous feature of these surface systems is the presence of atomic steps. Atomic steps are considered to strongly affect electron transport phenomena, because they potentially decouple neighboring surface terraces [12][13][14][15]. This could prevent superconducting currents from running over a long distance. The presence of supercurrents through atomic steps has indeed been demonstrated by direct electron transport measurements [2][3][4], and recent experiments indicated that atomic steps work as Josephson junctions [2,5]. Nevertheless, direct evidence of Josephson coupling has not been obtained yet, and possible local variation of its strength has remained an open issue. This problem is also closely related to Josephson junctions formed at the grain boundaries in thin films of high-T c cuprates, which are of technological importance [16,17].In this Letter, we report on compelling evidence of the Josephson coupling at atomic steps on the surface superconductor Si (111)Zero-bias conductance (ZBC) images taken with a low-temperature (LT) STM reveal that vortices are present at atomic steps after magnetic fields are applied. The crossover behavior from Pearl to Josephson vortices is evident from their characteristic elongated shapes and significant recovery of superconductivity within their cores. This identification is strongly supported by our numerical calculations, which clarify their dependence on the interterrace Josephson coupling at the atomic step.The experiment was performed using a UHV-LT-STM constructed at the Institute of Solid State Physics, University of Tokyo. The STM head was accommodated within a 3 He-based cryostat combined with a solenoid superconducting magnet, where magnetic field was applied in the normal direction to the sampl...

Indium coverage of the Si(111)- 7×3 -In surface

“…Among these reconstructions, the √7 × √3 has attracted much interest recently, because it shows a free-electron-like two dimensional metallic state [12,13] and superconductivity at about 3 K [14][15][16][17][18]. It is reported that two phases of the √7 × √3 reconstruction exist, which show slightly different appearances in scanning tunneling microscopy (STM) images, from which they derive their names: a hexagonal and a rectangular phase (denoted as "hex" and "rect", hereafter).…”

Impact of Surface Conditions on the Superconductivity of Si(111)-(√7 × √3)-In

“…Our results indicate that the atomic steps work as Josephson junctions and allow supercurrents to flow with a limited rate. Detailed results, discussions and theoretical calculations are presented elsewhere [9,10].…”

Superconducting nanoribbon with a constriction: A quantum-confined Josephson junction

“…In addition, impurities locally suppress superconductivity, which in superconducting nanowires can promote a phase slip center, giving rise to the broad temperature transition and residual resistance 25,26 . Very recently, a step in atomically thin films was found to have a strong effect on electronic transport 27,28 and vortex matter 24,29,30 , as a new paradigm in the interplay between the local defects and low-dimensional superconductivity. As an extended defect, the step does not only scatter electrons (leading to the modification on the overall electronic structure of the sample 31 ), but also affects the flow of superconduct-ing currents and the proximity-induced superconducting correlations 27,28 .…”