Nonvolatile control of valley related properties and valley-contrasting transport in multiferroic van der Waals heterostructures

It is highly desirable to tune valley-related property through reversible and electrically nonvolatile methods. Taking the VSiGeP4/Al2S3 heterostructure as an example, we demonstrate that the valley splitting and valley-contrasting transport in VSiGeP4 monolayer are significantly enhanced by using a ferroelectric Al2S3 substrate. The vertical strain and electric field can modulate valley splitting, magnetic anisotropy, and magnetic ground state. The valley splitting is mainly governed by charge transfer between the two sublayers. The valley splitting and valley-contrasting transport are highly tunable when the ferroelectric polarization state of the Al2S3 substrate is the upward direction. In contrast, the valley splitting is rather robust when the ferroelectric polarization state is switched to the opposite direction. Furthermore, we propose to use electrical conversion between two opposite ferroelectric polarization states to obtain nonvolatile control of valley-related properties. Our research provides a proof-of-concept scheme to achieve electrical control based on multiferroic van der Waals heterostructures.