Spin Hall Effect in Bilayer Graphene Combined with an Insulator up to Room Temperature

Enhanced Spin Relaxation Time in a 2D/1D Van Der Waals Hybrid Heterostructure

The key attraction of graphene in spintronics arises from its high electronic mobility and low intrinsic spin-orbit coupling (SOC), which enable long spin relaxation times. However, the weak SOC limits the ability to control spin currents within graphene. A promising strategy for enhancing the spin functionalities of graphene is to introduce proximity effects with other materials. In this context, molecular compounds show great potential for tuning the spin properties of graphene. Here, a novel fabrication methodology is presented that integrates molecular compounds with graphene-based spintronic nanodevices using stencil hexagonal boron nitride (hBN) masks, allowing us to investigate the resulting spin-related effects. First, our non-destructive fabrication technique, confirmed by micro-Raman spectroscopy, preserves the integrity of the molecular compound. Moreover, by combining experimental Hanle precession with a 3D spin diffusion model, it is demonstrated that fullerene (C60) molecules enhance the spin relaxation time of the graphene. The established fabrication methodology can be further expanded to integrate graphene with exotic molecular compounds, such as photochromic and spin cross-over molecules, enabling the exploration of proximity-induced spin phenomena and paving the way for spin-based multifunctional nanodevices.

Magnetotransport and Spin-Relaxation Signatures of the Radial Rashba and Dresselhaus Spin-Orbit Coupling in Proximitized Graphene

Graphene-based van der Waals heterostructures take advantage of tailoring spin-orbit coupling (SOC) in the graphene layer by the proximity effect. At long wavelength-saddled by the electronic states near the Dirac points-the proximitized features can be effectively modeled by the Hamiltonian involving novel SOC terms and allow for an admixture of the tangential and radial spin-textures-by the so-called Rashba angle θ_{R}. Taking such effective models we perform realistic large-scale magnetotransport calculations-transverse magnetic focusing and Dyakonov-Perel spin relaxation-and show that there are unique qualitative and quantitative features allowing for an unbiased experimental disentanglement of the conventional Rashba SOC from its novel radial counterpart, called here the radial Rashba SOC. Along with that, we propose a scheme for a direct estimation of the Rashba angle by exploring the magneto response symmetries when swapping an in-plane magnetic field. To complete the story, we analyze the magnetotransport and spin-relaxation signatures in the presence of an emergent Dresselhaus SOC and also provide some generic ramifications about possible scenarios of the radial superconducting diode effect.

Twist-angle-tunable spin texture in WSe2/graphene van der Waals heterostructures

Twist engineering has emerged as a powerful approach for modulating electronic properties in van der Waals heterostructures. While theoretical works have predicted the modulation of spin texture in graphene-based heterostructures by twist angle, experimental studies are lacking. Here, by performing spin precession experiments, we demonstrate tunability of the spin texture and associated spin-charge interconversion with twist angle in WSe2/graphene heterostructures. For specific twist angles, we detect a spin component radial with the electron's momentum, in addition to the standard orthogonal component. Our results show that the helicity of the spin texture can be reversed by twist angle, highlighting the critical role of the twist angle in the spin-orbit properties of WSe2/graphene heterostructures and paving the way for the development of spin-twistronic devices.

Ferroelectric Semimetals with α-Bi/SnSe van der Waals Heterostructures and Their Topological Currents

We show that proximity effects can be utilized to engineer van der Waals heterostructures (vdWHs) displaying semimetallic spin-ferroelectricity locking, where ferroelectricity and semimetallic spin states are confined to different layers, but are correlated by means of proximity effects. Our findings are supported by first principles calculations involving α-Bi/SnSe bilayers. We show that such systems support ferroelectrically switchable nonlinear anomalous Hall effect originating from large Berry curvature dipoles as well as direct and inverse spin Hall effects with giant bulk spin-charge interconversion efficiencies. The giant efficiencies are consequences of the proximity-induced semimetallic nature of low energy electron states, which are shown to behave as two-dimensional pseudo-Weyl fermions by means of symmetry analysis and first principles calculations as well as direct angle-resolved photoemission spectroscopy measurements.

Emerging Spintronic Materials and Functionalities

The explosive growth of the information era has put forward urgent requirements for ultrahigh-speed and extremely efficient computations. In direct contrary to charge-based computations, spintronics aims to use spins as information carriers for data storage, transmission, and decoding, to help fully realize electronic device miniaturization and high integration for next-generation computing technologies. Currently, many novel spintronic materials have been developed with unique properties and multifunctionalities, including organic semiconductors (OSCs), organic-inorganic hybrid perovskites (OIHPs), and 2D materials (2DMs). These materials are useful to fulfill the demand for developing diverse and advanced spintronic devices. Herein, these promising materials are systematically reviewed for advanced spintronic applications. Due to the distinct chemical and physical structures of OSCs, OIHPs, and 2DMs, their spintronic properties (spin transport and spin manipulation) are discussed separately. In addition, some multifunctionalities due to photoelectric and chiral-induced spin selectivity (CISS) are overviewed, including the spin-filter effect, spin-photovoltaics, spin-light emitting devices, and spin-transistor functions. Subsequently, challenges and future perspectives of using these multifunctional materials for the development of advanced spintronics are presented.

Gate-Tunable Spin Hall Effect in an All-Light-Element Heterostructure: Graphene with Copper Oxide

Graphene is a light material for long-distance spin transport due to its low spin-orbit coupling, which at the same time is the main drawback for exhibiting a sizable spin Hall effect. Decoration by light atoms has been predicted to enhance the spin Hall angle in graphene while retaining a long spin diffusion length. Here, we combine a light metal oxide (oxidized Cu) with graphene to induce the spin Hall effect. Its efficiency, given by the product of the spin Hall angle and the spin diffusion length, can be tuned with the Fermi level position, exhibiting a maximum (1.8 ± 0.6 nm at 100 K) around the charge neutrality point. This all-light-element heterostructure shows a larger efficiency than conventional spin Hall materials. The gate-tunable spin Hall effect is observed up to room temperature. Our experimental demonstration provides an efficient spin-to-charge conversion system free from heavy metals and compatible with large-scale fabrication.

CVD Bilayer Graphene Spin Valves with 26 μm Spin Diffusion Length at Room Temperature

We present inverted spin-valve devices fabricated from chemical vapor deposition (CVD)-grown bilayer graphene (BLG) that show more than a doubling in device performance at room temperature compared to state-of-the-art bilayer graphene spin valves. This is made possible by a polydimethylsiloxane droplet-assisted full-dry transfer technique that compensates for previous process drawbacks in device fabrication. Gate dependent Hanle measurements reveal spin lifetimes of up to 5.8 ns and a spin diffusion length of up to 26 μm at room temperature combined with a charge carrier mobility of about 24 000 cm²(V s)^-1 for the best device. Our results demonstrate that CVD-grown BLG shows equally good room temperature spin transport properties as both CVD-grown single-layer graphene and even exfoliated single-layer graphene.