Superconductivity at the two-dimensional limit.

Superconductivity at the two-dimensional limit in crystalline films with only one unit cell thick or one quantum well channel has become a frontier in the field of superconductivity. In this paper, we briefly review the recent experimental detections of superconductivity at the two-dimensional limit and corresponding Berezinskii-Kosterlitz-Thouless (BKT) transitions using imaging, spectroscopy and transport techniques, such as one-monolayer Pb/In films on Si(lll) substrates, one-unit-cell FeSe films on SrTiO₃ (001) substrates, and two-monolayer Ga films on GaN(0001) substrates. Due to anisotropy, quantum size effects from dimension limitation, and interface effects between the film and the substrate, superconducting parameters such as critical temperature, Bardeen-Cooper-Schrieffer (BCS) ratio and critical magnetic fields in thin films can be significantly different from those in corresponding bulk materials. Furthermore, considering quasi-two-dimensional layered structure in high-Tc superconductors and dissipation problem in electronic integrated circuits, the investigation of superconductivity at the two-dimensional limit is expected not only to reveal new physical phenomena or properties, but also to further understand high-T_c superconductivity and explore new high-T_c superconductors, as well as to develop new generation of dissipationless electronic devices and low-dissipation integrated circuits. [ABSTRACT FROM AUTHOR]