Persistent superconductivity in ultrathin Pb films: a scanning tunneling spectroscopy study

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Superconducting properties are sensitive to material dimensions, especially in ultrathin films.
• Quantum confinement effects can significantly alter electronic states and critical temperatures in nanostructures.

Purpose of the Study:

• To investigate the superconducting energy gap and transition temperature (Tc) in epitaxially grown lead (Pb) films.
• To understand the relationship between film thickness, quantum-well states, and superconducting properties.
• To explore quantum phenomena in ultrathin superconducting films.

Main Methods:

• Utilized low-temperature scanning tunneling microscopy (LT-STM) to probe superconducting properties.
• Examined epitaxially grown Pb films with layer thicknesses ranging from 5 to 18 monolayers (ML).
• Measured quantum-well states above the superconducting transition temperature (Tc).

Main Results:

• Observed persistent quantum oscillations in both the energy gap and transition temperature (Tc) as a function of film thickness.
• Found no suppression of superconducting properties down to the lowest measured thicknesses.
• Demonstrated a direct correlation between Tc oscillations and the density of states oscillations at the Fermi level (E(F)).

Conclusions:

• The observed quantum oscillations in Tc are driven by the electronic density of states at the Fermi level.
• The oscillations exhibit a bilayer periodicity, modulated by quantum beats, linked to Fermi wavelength and film thickness.
• Ultrathin Pb films maintain robust superconducting properties, exhibiting predictable quantum phenomena with varying thickness.