Spin-orbit-mediated proximity coupling at a magnetic van der Waals interface

Two-dimensional (2D) quantum materials and their integrated superstructures provide emergent phenomena associated with reduced dimensionality, modified lattice symmetry, and enhanced proximity coupling. A remarkable example is Ising superconductivity emerging in a non-centrosymmetric 2D superconductor with broken in-plane inversion symmetry as represented by 2D NbSe₂, where strong Zeeman-type spin-orbit interaction (SOI) locks the orientation of the spins of Cooper pairs to the out-of-plane direction, providing exotic non-BCS superconducting states. In this presentation, we demonstrate a unique proximity coupling between such out-of-plane spin-polarized electrons in 2D NbSe₂ and isotropic local spins in a newly-developed 2D Heisenberg ferromagnet V₅Se₈ [1] across a van der Waals interface [2, 3]. We will in particular focus on the specific regime, where the number of the V₅Se₈ layer was decreased down to the 2D limit so that the transport properties were dominated by NbSe₂ [3]. Very interestingly, we found that the sign of the anomalous Hall effect (AHE) of those samples were positive at the lowest temperature, which was opposite to those of the V₅Se₈ individual films. We also found that the AHE signal of those samples was enhanced with the in-plane magnetic fields, suggesting an additional contribution to the AHE signal except magnetization. We verify by band structure calculations that those unprecedented behavior could be well understood by accepting the idea that NbSe₂ is in a ferromagnetic/ferrovalley state, where characteristic Zeeman-type SOI plays an essential role.

 

References:

[1] M. Nakano et al., Nano Lett. 19, 8806 (2019).

[2] H. Matsuoka et al., Nano Lett. 21, 1807 (2021).

[3] H. Matsuoka et al., submitted.