Role of steps on Pb atomic-layer superconductivity

Atomic-layer superconductors [1] exhibit various unique characteristics. One of the features is the enhancement of the in-plane critical magnetic field. The presence of steps, which work as a Josephson barrier [2], is inevitable. It is thus expected that the weakened coupling between terraces confines cooper pairs within the terraces and modifies superconductivity depending on the terrace width.
Pb monolayers on a Si(111) substrate is known to form various superconducting phases. Using scanning tunneling microscopy (STM), we found a√3×√43 superconductivity phase still remains on narrow terraces (< 150 nm) even under out-of-plane magnetic fields above its critical magnetic field (190 mT). In addition, on a striped incommensurate (SIC) phase formed on a 1.1 degrees tilted vicinal Si(111) substrate, where 15 nm-narrow terraces covers the whole surface, we observed suppression of the superconductivity breaking against out-of-plane magnetic field. Our results open up the possibility of creating superconducting materials whose the critical magnetic fields of all directions are enhanced in a macroscopic level.

References:
[1] T. Zhang et al., Nature Phys., 6, 104 (2010)
[2] S. Yoshizawa et al., Phys. Rev. Lett. 113, 247004 (2014)