- The paper develops a theory quantifying spin accumulation in chiral semimetals where Weyl nodes are energetically separated.
- It employs diagrammatic perturbation theory to derive coupled spin-charge diffusion equations that explain complex transport phenomena.
- Numerical results reveal a nonmonotonic Fermi energy dependency and a spin-valve-like magnetoresistance with promising spintronic applications.
The paper "Current-Induced Spin Accumulation and Magnetoresistance in Chiral Semimetals" investigates the theoretical framework underlying spin-momentum locking and its resultant effects in Weyl semimetals. The focus centers on the role of broken inversion and mirror symmetries in chiral semimetals wherein Weyl nodes of opposite chirality occur at different energies, in contrast to traditional bulk Weyl semimetals where these nodes cancel out any net spin accumulation.
Key Findings and Contributions
The paper develops a generalized theory to quantify spin accumulation in response to an electrical current in chiral topological semimetals. It presents a minimal theoretical model considering a pair of linearly dispersing Weyl nodes separated in both momentum and energy. By incorporating impurity scattering using a diagrammatic perturbation theory, the researchers derived coupled spin-charge diffusion equations that capture the interaction between spin and charge transport.
The key finding is that spin accumulation is maximized when the Fermi energy aligns with one of the nodes, achieving an effective spin polarization equivalent to an isolated node. This is a significant departure from previous understandings where such effects were considered entirely negligible in bulk semimetals.
Numerical Insights and Implications
Noteworthy numerical insights include the demonstration that the spin accumulation exhibits a nonmonotonic dependency on the Fermi energy. The maximum value, equivalent to ℏ/2 per electron, aligns with conditions where the Fermi energy matches one of the Weyl nodes, while both at charge neutrality and far from the nodes, the effect dissipates. Furthermore, a novel magnetoresistance mechanism emerges, contingent on nonequilibrium spin density induced by spin-polarized current injection. This results in an additional contribution to voltage affected by the magnetization's orientation, leading to a distinct spin-valve-like effect.
The implications of these findings extend both practically and theoretically. Practically, these results offer potential advancements in spintronic applications, wherein control over spin currents is vital. Chiral semimetals such as CoSi and RhSi present promising platforms for experimental observation of these theoretical predictions due to their complex electronic structures characterized by non-trivial topology.
Future Directions
This research opens several avenues for further exploration. Experimentally, verifying the theory in chiral semimetal samples is crucial, potentially accounting for the more elaborate electronic nature of real materials as opposed to the idealized model presented. Theoretically, extending studies to include interactions between different transport phenomena, as well as disorder effects beyond the self-consistent Born approximation, could enrich the comprehension of spin-related phenomena in topologically nontrivial systems.
In conclusion, the paper provides robust theoretical insights into spin phenomena in chiral semimetals, laying groundwork for experimental validations and future studies in topological materials and spintronics.
