Inhomogeneous Superconductivity Onset in FeSe Studied by Transport Properties

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Heterogeneous superconductivity onset is typical in high-temperature superconductors.
• Superconductivity often initiates as isolated domains in anisotropic materials like FeSe.
• Transport measurements reveal SC domain structure and size.

Purpose of the Study:

• Investigate the impact of sample thickness on superconductivity in FeSe.
• Determine the aspect ratio and size of superconducting domains.
• Develop a method to estimate SC domain aspect ratio from Tc anisotropy.

Main Methods:

• Fabrication of FeSe mesa structures using focused ion beam (FIB) for interlayer resistivity measurements.
• Temperature-dependent measurement of both interlayer and intralayer resistivity.
• Analytical and numerical calculations to analyze experimental data.

Main Results:

• Superconducting transition temperature (Tc) increases from 8 K in bulk FeSe to 12 K in ~40 nm thick microbridges.
• SC domain aspect ratio and size are consistent with resistivity and diamagnetic response measurements.
• A method for estimating SC domain aspect ratio from Tc anisotropy in thin samples was proposed.

Conclusions:

• Sample thickness significantly influences the superconducting transition temperature in FeSe.
• The study provides a method for characterizing SC domains in anisotropic superconductors.
• Discusses the relationship between nematic and superconducting domains in FeSe.