Monolayers on Ferromagnetic EuS Substrates*

We have compared the Zeeman splitting ΔE of the A exciton in MoS₂ monolayers deposited on SiO₂/Si with those from MoS deposited on ferromagnetic EuS substrates. The ΔE is defined as the energy difference between the σ- and the σ+ exciton components with the magnetic field perpendicular to the sample plane. The Zeeman splitting for the SiO₂ substrate samples is linear in magnetic field with a slope of 0.2 meV/T. The samples on EuS substrates behave in a different way: For |B|< 1 T the slope of the ΔE vs B plotbecomes ~ -2 meV/T. Here 1 T is the field at which the EuS magnetization saturates. For |B|>1 T the slope changes sign and becomes ~ 0.8 meV/T. In the related WSe₂ /EuS system, the slope for |B|>1T returns to the 0.2 meV/T¹, i.e. the exchange enhanced valley splitting saturates as the magnetization of EuS saturates. The enhanced valley splitting with opposite signs at different field ranges for MoS₂ on EuS suggests competing mechanisms for valley splitting.

1 Zhao, C. et al,. Nat Nanotechnol 12, 757-762, (2017)