Spin-orbit enabled unconventional Stoner magnetism.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Magnetism

Background:

• The Stoner instability is crucial for understanding metallic ferromagnets, involving Coulomb repulsion, Pauli exclusion, and spin degeneracy.
• In materials with spin-orbit coupling, fermionic spin generalizes to pseudospin, usually assumed to share spin's symmetry properties.

Purpose of the Study:

• To identify a distinct symmetry of pseudospin that prevents its coupling to a Zeeman field.
• To explore the implications of this 'spinless' pseudospin property on magnetism and superconductivity in specific nonsymmorphic space groups.

Main Methods:

• Theoretical identification of a novel pseudospin symmetry.
• Analysis of Fermi surfaces and Coulomb repulsion effects.
• Investigation of implications for magnetic instabilities and superconducting properties.

Main Results:

• A 'spinless' pseudospin symmetry was identified, forbidding coupling to Zeeman fields in five nonsymmorphic space groups.
• Stoner instabilities driven by this pseudospin lead to novel magnetic states: time-reversal breaking, vanishing magnetization, noncollinear structures, and momentum-dependent spin-splittings.
• This spinless pseudospin eliminates paramagnetic limiting in superconductors across all pairing symmetries and field orientations.

Conclusions:

• The discovered 'spinless' pseudospin symmetry fundamentally alters magnetic and superconducting behaviors.
• This property enables new types of magnetic orders and enhances superconducting critical fields.
• Potential applications exist in materials like UCoGe and NiS[Formula: see text]Se[Formula: see text].