Tailoring The Rashba-Induced Spin-To-Charge Conversion in 2D Transition Metal Dichalcogenides Interfaced with Oxide Ferroelectrics

The direct and inverse Rashba-Edelstein effect in condensed matter is a viable source of charge-to-spin interconversion, towards the realisation of next-generation spintronic devices. One promising way of creating Rashba spin-orbit coupling (SOC) in an otherwise centrosymmetric material system is to interface it with a ferroelectric crystal, breaking inversion symmetry with the local electric field at the interface.<br/><br/>Two-dimensional (2D) crystals have emerged as a new class of materials that can exhibit a large range of quantum phenomena such as superconductivity, 2D magnetism, and non-trivial topological phases [1], [2]. Of these quantum phenomena, the Rashba effect has gained popularity recently as a result of its applicability to create charge-to-spin interconversion for next-generation spintronics devices. Highly stable PtSe₂ is one such 2D material which has a centrosymmetric crystal unit cell and a band-structure that evolves drastically as a function of the number of monolayers deposited, evolving from a high band-gap semiconductor to a semi-metal [3]. Interfacing a 2D material with a ferroelectric (FE) crystal applies a strong local electric field at the interface which breaks the inversion symmetry and triggers the interfacial Rashba effect in the 2D layer. Importantly, the sign of the Rashba spin-orbit coupling depends on the direction of the FE polarisation, such that the spin texture chirality should reverse upon a change in direction of the FE polarisation [4]. This forms the basis of the functionality of a low-power <b>F</b>erro<b>E</b>lectric <b>S</b>pin-<b>O</b>rbit (FESO) device.<br/><br/>In this work, we grow 2D materials such as PtSe₂using molecular beam epitaxy and use a wet transfer process to interface them with a variety of ferroelectric surfaces such as LiNbO₃ substrates and BiFeO₃ thin fims. The spin-to-charge conversion characteristics are then examined using a variety of experimental techniques and compared between samples with different ferroelectric polarisation directions and assessed in the context of a spin-to-charge conversion FESO device.<br/><br/><br/>[1] A. K. Geim and I. V. Grigorieva, ‘Van der Waals heterostructures’, Nature, vol. 499, no. 7459, pp. 419–425, Jul. 2013, doi: 10.1038/nature12385.<br/>[2] F. Giustino et al., ‘The 2021 quantum materials roadmap’, J. Phys. Mater., vol. 3, no. 4, p. 042006, Jan. 2021, doi: 10.1088/2515-7639/abb74e.<br/>[3] L. Zhang et al., ‘Precise Layer-Dependent Electronic Structure of MBE-Grown PtSe2’, Advanced Electronic Materials, vol. 7, no. 11, p. 2100559, 2021, doi: 10.1002/aelm.202100559.<br/>[4] S. Picozzi, ‘Ferroelectric Rashba semiconductors as a novel class of multifunctional materials’, Frontiers in Physics, vol. 2, 2014, Accessed: Mar. 10, 2023. [Online]. Available: https://www.frontiersin.org/articles/10.3389/fphy.2014.00010