Spin resonance from spin-pseudospin coupling of Dirac electrons in van der Waals heterostructures

Atomically thin character of two-dimensional (2D) materials ensures that their physical properties are strongly dominated by proximity effects [1]. The enhancement of spin-orbit coupling and exchange interaction due to the proximitization, a key factor for better spin-charge interconversion and efficient spin-orbit torques of 2D systems [2], remains challenging to be addressed experimentally. In this work we have come up with the new physical realization of the electronic spin resonance induced by ac-electric field in proximitized Dirac materials, including graphene monolayer [3]. We disclose the role of coupled spin-pseudospin dynamics for the dynamical spin response of Dirac electrons upon oscillating electric field and reveal a number of unexpected features in the spin resonance absorption. Among other, the spin-pseudospin coupling manifests itself in an enhanced spin-flip absorption controlled by the position of the Fermi energy and leads to an anomalous polarization structure strikingly different from usual polarization rules of the spin resonance. We demonstrate these new features based on the rigorous Kubo formula evaluation of the optical conductivity, as well as we provide a qualitative mean-field theory for the coupled spin-pseudospin dynamics. Encouraged by our findings we discuss the prospect of the spin resonance technique for experimental diagnostics of different spin splitting terms emerging in proximitized van der Waals heterostructures.

References

[1] I. Zutic et al., “Proximitized materials”, Materials Today, 22, 85 (2019).

[2] J. F. Sierra, J. Fabian, R. K. Kawakami, S. Roche, and S. O. Valenzuela, Nat. Nanotech. 16, 856 (2021).

[3] K.S. Denisov, I.V. Rozhansky, S.O. Valenzuela and I. Zutic, under review in Phys. Rev. Lett. (2023).