Weyl-mediated helical magnetism in NdAlSi

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Weyl semimetals exhibit unique electronic properties due to emergent relativistic quasiparticles called Weyl fermions.
• Observed phenomena include surface Fermi arcs, anomalous Hall effect, and negative magnetoresistance, primarily linked to electronic transport.
• The potential for Weyl fermions to support collective phenomena, such as magnetism, remains less understood.

Purpose of the Study:

• To investigate collective phenomena driven by Weyl fermions in a Weyl semimetal.
• To explore the relationship between topological electronic structures and magnetic ordering in NdAlSi.
• To identify the underlying interactions promoting magnetic structures in Weyl semimetals.

Main Methods:

• Neutron diffraction to characterize magnetic order.
• Density functional theory (DFT) calculations to analyze electronic band structure and Fermi pockets.
• Quantum oscillation measurements to probe topological electronic properties.

Main Results:

• A long-wavelength helical magnetic order was discovered in the Weyl semimetal NdAlSi.
• The magnetic order's periodicity is directly linked to the nesting vector of two topologically non-trivial Fermi pockets.
• Bond-oriented Dzyaloshinskii-Moriya interactions, driven by Weyl exchange processes, promote the chiral transverse spin structure.

Conclusions:

• Weyl fermions can drive collective magnetism, exemplified by the helical magnetic order in NdAlSi.
• Topological Fermi pockets and associated nesting vectors play a crucial role in establishing magnetic order.
• This work establishes a rare instance of Weyl fermions inducing collective magnetic phenomena, expanding the understanding of quantum materials.