Spin-orbit interactions and the nematicity observed in the fe-based superconductors

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Iron-based superconductors exhibit complex electronic properties.
• Understanding the electronic band structure is crucial for explaining their superconducting mechanisms.
• Nematicity, a key characteristic, requires a microscopic explanation.

Purpose of the Study:

• To investigate the electronic band structure of FeTe0.5Se0.5 near the Brillouin zone center.
• To elucidate the origins of orbital ordering and its relation to nematicity.
• To provide a microscopic understanding of the electronic behavior in iron-based superconductors.

Main Methods:

• High-resolution angle-resolved photoelectron spectroscopy (ARPES) was employed to probe the electronic band structure.
• First-principles calculations were performed for both bulk and thin film FeTe0.5Se0.5.
• Analysis focused on the electronic band separation and orbital characteristics at the zone center.

Main Results:

• ARPES measurements showed a consistent separation between the α1 and α2 electronic bands.
• The α1 band exhibited minimal dependence on k_z momentum.
• Calculations revealed that antiferromagnetic coupling and spin-orbit effects lift the degeneracy of Fe d_xz and d_yz orbitals, inducing orbital ordering.

Conclusions:

• The observed orbital ordering is a direct consequence of electronic interactions and spin-orbit coupling.
• These findings establish a microscopic foundation for the nematicity observed in iron-based superconductors.
• The study offers critical insights into the fundamental physics governing the properties of these materials.