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Dynamic nuclear polarization from topological insulator helical edge states
摘要： Topological insulators are promising for spintronics and related technologies due to their spin-momentum-locked edge states, which are protected by time-reversal symmetry. In addition to the unique fundamental physics that arises in these systems, the potential technological applications of these protected states have also been driving TI research over the past decade. However, most known topological insulator materials naturally contain spinful nuclei, and their hyperfine coupling to helical edge states intrinsically breaks time-reversal symmetry, removing the topological protection and enabling the buildup of dynamic nuclear spin polarization through hyperfine-assisted backscattering. Here, we calculate the scattering probabilities and nuclear polarization for edge channels containing up to 34 nuclear spins using a numerically exact analysis that exploits the symmetries of the problem to drastically reduce the computational complexity. We then show the emergence of universal scaling properties that allow us to extrapolate our findings to vastly larger and experimentally relevant system sizes. We find that significant nuclear polarization can result from relatively weak helical edge currents, suggesting that it may be an important factor affecting spin transport in topological insulator devices.
关键词： Hyperfine coupling,Dynamic nuclear polarization,Helical edge states,Topological insulators,Spintronics
更新于2025-09-04 15:30:14
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Effects of spin-orbit coupling on the optical response of a material
摘要： We investigate the effects of spin-orbit coupling on the optical response of materials. In particular, we study the effects of the commutator between the spin-orbit coupling part of the potential and the position operator on the optical matrix elements using density functional theory calculations within the generalized gradient approximation. By means of a formalism that separates a fully relativistic Kleinman-Bylander pseudopotential into the scalar-relativistic and spin-orbit-coupling parts, we calculate the contribution of the commutator arising from spin-orbit coupling to the squared optical matrix elements of isolated atoms, monolayer transition-metal dichalcogenides, and topological insulators. In the case of isolated atoms from H (Z = 1) to Bi (Z = 83), the contribution of spin-orbit coupling to the squared matrix elements can be as large as 14%. On the other hand, in the cases of monolayer transition-metal dichalcogenides and topological insulators, we find that this contribution is less than 1% and that it is sufficient to calculate the optical matrix elements and subsequent physical quantities without considering the commutator arising from spin-orbit coupling.
关键词： optical response,spin-orbit coupling,transition-metal dichalcogenides,topological insulators,density functional theory
更新于2025-09-04 15:30:14