Revealing Spin and Spatial Symmetry Decoupling: New Insights into Magnetic Systems with Dzyaloshinskii-Moriya Interaction (2502.00457v1)

Abstract: It is widely accepted that spin-orbit coupling (SOC) generally locks spin and spatial degrees of freedom, as a result, the spin, despite being an axial vector, is fixed and cannot rotate independently, and the magnetic system should be described by magnetic space groups (MSGs). While as a new type of group, spin space groups (SSGs) have been introduced to approximately describe the symmetry of magnetic systems with negligible SOC, and received significant attention recently. In this work, we prove that in two cases of coplanar spin configurations, there are spin-only operations that strictly hold even with considerable Dzyaloshinskii-Moriya interaction (DMI), and the symmetry of their spin models could be described by the spin-coplanar SSG. In addition, we also find that for spin-collinear cases, regardless the strength of DMI, the magnon systems within the framework of linear spin wave theory (LSWT) also preserve the decoupled spin and spatial rotations, but the symmetry does not belong to the conventional definitions of collinear spin groups. Finally, we discuss the potential realization of these novel symmetries for magnetic candidate materials in rod, layer, and three-dimensional (3D) space groups. Our work extends the applicability of SSGs to magnetic materials with heavy elements, and provides new avenues for exploring novel physical phenomena in magnon topology and transport.

• The paper reveals that DMI decouples spin and spatial symmetries in both coplanar and collinear configurations.
• It employs symmetry analysis and LSWT to characterize magnon transport, suggesting potential for pure spin current generation.
• The study identifies candidate 2D and 3D materials where decoupled symmetry properties enable novel magnetic states and device applications.

Decoupling Spin and Spatial Symmetry in Magnetic Systems Influenced by Dzyaloshinskii-Moriya Interaction

The paper "Revealing Spin and Spatial Symmetry Decoupling: New Insights into Magnetic Systems with Dzyaloshinskii-Moriya Interaction" addresses the profound influence of Dzyaloshinskii-Moriya interaction (DMI) on the symmetry properties of magnetic systems. The research delineates scenarios under which spin and spatial rotations remain decoupled even in the presence of significant DMI, challenging the conventional understanding where spin-orbit coupling (SOC) generally synchronizes these two degrees of freedom.

Detailed Insights and Methodology

The paper investigates magnetic systems typically characterized by magnetic space groups (MSGs) due to SOC which locks spin and spatial degrees, preventing independent spin rotations. Introduced as an alternative framework, spin space groups (SSGs) offer higher symmetry descriptions for materials with negligible SOC. This paper expounds the classification and applicability of SSGs to materials where SOC is non-negligible due to substantial DMI, particularly in coplanar and collinear spin configurations.

Key Findings

1. Spin-Coplanar and Collinear Configurations: The authors identify two key magnetic configurations where DMI does not completely couple spatial and spin symmetries:
   • Coplanar Spin Systems: In planar systems (2D), where magnetic atoms lie in the plane with horizontal mirror symmetry, DMI aligns perpendicular to the plane. Similarly, 1D chain systems with C$_{2z}$ symmetry align DMI along the axis. These configurations maintain the structure of spin-coplanar SSGs, retaining symmetry operations such as time reversal combined with spin rotations.
   • Collinear Spin Configurations: For collinear spins within LSWT, SSG-like symmetries persist despite massive DMI. An interesting observation is that only certain spin operations are retained while others are suppressed by the presence of DMI.
2. Magnon Transport and Spintronics Implications: The research highlights significant implications for magnon transport, predicting possible pure spin current generation without thermal current due to preserved symmetries. The elucidation of how intact SSG-related symmetries influence magnon behaviors offers potential advancements in the design of spintronic devices.
3. Candidate Materials Identification: The authors provide a comprehensive list of materials, identified through symmetry criteria, in which the decoupled symmetry persists despite DMI. These include 2D materials categorized using layer groups and 3D materials by their associated space groups.

Theoretical and Practical Implications

The paper broadens the theoretical framework of symmetry in magnetic systems, presenting a nuanced understanding of SSG application in materials with pronounced DMI. This extension is particularly valuable in predicting novel magnetic states and phenomena in complex materials, such as topological magnon systems, where unconventional symmetry considerations are pivotal.

The exploration of the influence of DMI on SSG symmetries enriches the discourse on how magnon topological properties and transport behaviors can be harnessed and tailored. This is particularly critical in fields like magnonics and spintronics where understanding and controlling wave propagation and spin currents hold significant technological promise.

In conclusion, this paper contributes to the enhancement of symmetry theory in condensed matter physics and provides a structured pathway for discovering emergent phenomena in magnetic materials through the intersection of DMI and SSGs. Future research may build on these findings to further explore material-specific applications and the practical engineering of devices utilizing these novel symmetry considerations.