Non-volatile Valley Spin Valve based on 2D Ferroelectric MoS₂

A spin valve is a fundamental device concept in spintronics, where electron transmission is controlled by the alignment of magnetic moments in two ferromagnetic layers. Recently, the relevant concept has been proposed in valleytronics, where a valley spin valve (VSV) utilizes the valley degree of freedom and spin-valley locking to achieve a similar valve effect without relying on magnetism.¹ In this work, we propose to make VSV non-volatile by using a two-dimensional ferroelectric semiconductor whose electrical resistance is controlled by the ferroelectric domain wall between the two uniformly polarized domains. Focusing on the 1T’’ phase of MoS₂, which is known for its monolayer ferroelectricity, we employ density functional theory and quantum transport calculations and demonstrate a giant resistance change up to 10⁷ when switching between the uniformly polarized state and the state with oppositely polarized domains separated by a domain wall. This VSV effect occurs due to transmission being strongly dependent on the matching (mismatching) of the valley-dependent spin polarizations in the two domains with the same (opposite) ferroelectric polarization orientations, when the chemical potential of 1T’’-MoS₂ lies within the spin-split valleys. Our results offer a new approach to realize high-performance, non-volatile valleytronic devices.

1. L. L. Tao, E. Y. Tsymbal, Two-dimensional spin-valley locking spin valve. Phys. Rev. B 100, 161110(R) (2019).