Protected Fe valence in quasi-two-dimensional α-FeSi2

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Iron disilicide (α-FeSi2) shares structural similarities with iron-based superconductors like LiFeAs.
• Understanding α-FeSi2's electronic properties is crucial for exploring unconventional superconductivity.

Purpose of the Study:

• To conduct a comprehensive study of the high-temperature α-phase of iron disilicide.
• To investigate its potential for unconventional superconductivity by examining its electronic and magnetic properties.

Main Methods:

• Measurements of magnetic susceptibility, magnetization, heat capacity, and resistivity on single crystals.
• Theoretical calculations including band theory and many-body approaches.

Main Results:

• α-FeSi2 exhibits metallic behavior down to 1.8 K without magnetic ordering.
• Electronic correlations and paramagnetism are weaker than in pnictides.
• Vacancy formation and doping (Mn, Co) have limited impact on electronic properties.
• Smaller inter-iron layer spacing leads to different orbital symmetries near the Fermi level.

Conclusions:

• α-FeSi2 is a metal with modest electronic correlations, differing from unconventional superconductors.
• The distinct orbital character due to reduced inter-iron spacing may explain the absence of superconductivity.
• Findings provide insights into pairing mechanisms in iron-based superconductors.