Lateral Quantum Confinement Effect on High-T_C Superconducting FeSe Monolayer

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Investigating superconductivity in reduced dimensions is crucial for understanding high-temperature superconductors.
• The quantum confinement effect's influence on high-temperature superconductors remains poorly understood.
• Spatially confined superconducting systems offer insights into fundamental superconducting mechanisms.

Purpose of the Study:

• To explore the impact of lateral quantum confinement on the superconductivity of iron selenide (FeSe) monolayers.
• To investigate the electronic properties and superconducting states in confined FeSe monolayer systems.
• To understand the transition between Bardeen-Cooper-Schrieffer and Bose-Einstein condensate states in low-dimensional superconductors.

Main Methods:

• Epitaxial growth of FeSe films with sub-unit cell coverage on strontium titanate (SrTiO3) substrates.
• Scanning tunneling spectroscopy (STS) measurements to probe electronic states and superconductivity.
• Comparative analysis of uniform FeSe monolayer regions and boundary peninsula regions.

Main Results:

• Laterally confined FeSe monolayers exhibit reduced Fermi energy in boundary regions.
• Superconductivity remains undiminished in these confined boundary regions.
• Isolated FeSe monolayer islands demonstrate superconductivity in smaller volumes, fulfilling Anderson's criterion.

Conclusions:

• Lateral quantum confinement influences superconductivity in unconventional superconductors like FeSe.
• A potential crossover from Bardeen-Cooper-Schrieffer to Bose-Einstein condensate states is observed.
• This research advances the understanding of high-temperature superconductivity in low-dimensional materials.