The temperature dependence of anisotropic conductivity of a quasi-one-dimensional metallic surface, Si(111)4 × 1-In, was measured by a variable-temperature four-tip scanning tunneling microscope. Using the square four-point probe method, we succeeded in measuring the conductivity parallel and perpendicular to the In chains independently as a function of temperature. It was shown that the conductivity perpendicular to the In chains was mainly the conductivity of the space-charge layer of the substrate. Moreover, it was clarified that it strongly depends on the substrate flashing temperature and this sometimes hindered the anisotropic conductivity at low temperatures. In contrast, the conductivity parallel to In chains was clearly dominated by the surface states and decreased drastically around 110 K by the well-known 4 × 1 to 8 × 2 metal-insulator transition. The low temperature 8 × 2 phase had an energy gap as large as ∼250 meV, consistent with previous photoemission reports.

The strongly connected or coupled grain boundaries (GBs) between adjacent grains and their macroembodiment as flowing intergrain supercurrents crossing the GBs inside multiseeded bulk high-temperature superconductors were elucidated by trapped-flux evaluation. Trapped-field measurements, after cutting and polishing two multiseeded YBCO bulk samples, were conducted to present the existence of coupled GBs and their distribution along the c-axis growth. The intensive trapped-flux density observed near the GB areas inside the whole sample is direct evidence of a strongly connected or coupled GB. The relatively strong trapped flux near the GB areas and the significant improvement of the total trapped flux compared with the isolated single-grain bulks were ascribed to the intergrain supercurrent flowing across the GBs in large macroscopic loops with coordination of the intragrain supercurrent circulating in each grain of the multiseeded bulk. Based on the experimental results, a simplified simulation model that incorporates two forms of the intra-and intersupercurrents flowing inside the multiseeded bulk is introduced to reproduce the trapped-flux density features, and qualitative agreement is obtained by comparison with the experimental ones.Index Terms-Bulk high-temperature superconductors (HTSCs), grain boundary (GB) coupling, intra-and intergrain current, multiseeded bulks, trapped magnetic flux.

We performed in situ conductivity measurements by multiple microscopic probes of Ag nanofilms grown on a periodic array of indium atomic wires on Si(111). Within the investigated thickness range the transport properties differ markedly from the bulk case. The ratio between the in-plane conductivity along and perpendicular to the In wires is 1.4 for the 3 monolayer (0.7 nm) thick Ag film and approaches unity with increasing film thickness. The observed anisotropy at the initial stage of the film growth is far larger than expected from the quasi-one-dimensional quantum well electronic structure of the films and ascribed to the carrier scattering at the film/vacuum and film/substrate interfaces. Our findings show that an ordered monolayer inserted at the interface enables drastic changes of the transport behavior of the whole metal nanofilm.

No abstract