Unconventional Charge-to-Spin Conversion in Graphene/ MoTe2 van der Waals Heterostructures

Abstract

Spin-charge interconversion (SCI) is a central phenomenon to the development of spintronic devices from materials with strong spin-orbit coupling (SOC). In the case of materials with high crystal symmetry, the only allowed SCI processes are those where the spin-current, charge-current, and spin-polarization directions are orthogonal to each other. Consequently, standard SCI experiments are designed to maximize the signals arising from the SCI processes with conventional mutually orthogonal geometry. However, in low-symmetry materials, certain nonorthogonal SCI processes are also allowed. Since the standard SCI experiment is limited to charge current flowing only in one direction in the SOC material, certain allowed SCI configurations remain unexplored. Here, we perform a thorough SCI study in a graphene-based lateral spin valve combined with low-symmetry MoTe 2 . Due to a very low contact resistance between the two materials, we can detect SCI signals using both a standard configuration, where the charge current is applied along MoTe 2 , and a recently introduced [three-dimensional-(3D) current] configuration, where the charge-current flow can be controlled in three directions within the heterostructure. As a result, we observe three different SCI components, one orthogonal and two nonorthogonal, adding valuable insight into the SCI processes in low-symmetry materials. The large SCI signals obtained at room temperature, along with the versatility of the 3D-current configuration, provide feasibility and flexibility to the design of the next generation of spin-based devices.

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

“…The pure charge-to-spin precession signal Δ R CSC with out-of-plane spin polarization (due to the SHE), plotted in Figure (g), has been obtained as follows: (1) subtracting the R NL curves between the positive ( R NL ↑ ) and negative ( R NL ↓ ) alignment of the F1 magnetization, followed by (2) an antisymmetrization of the obtained curve with respect to the magnetic field. The first step removes any initial-magnetization-independent components, such as local magnetoresistance, ordinary Hall effect, and conventional EE. , The second step eliminates the possible contribution of unconventional charge-to-spin conversion with spins polarized along y , which has been observed in some van der Waals heterostructures. − The reciprocal experiment (inverse SHE) is shown in the Supporting Information Figure S11 and confirms that we are in the linear response regime. A control experiment in a reference device without CuO x as an adlayer exhibits no spin-to-charge signal (see Supporting Information Figure S10).…”

Transition Metal Dichalcogenides: Making Atomic‐Level Magnetism Tunable with Light at Room Temperature

“…The "twisting" effect has been reported to significantly alter the magnetic and valleytronic properties of 2D-TMDs. [129,[152][153][154][155][156] Twisting graphene from a 2D-TMD in a 2D-TMD/graphene heterostructure can enhance the valley Zeeman and Rashba effects, [129,152] as well as the charge-to-spin conversion efficiency. [153,154] By tailoring the atomic interface between twisted bilayer graphene and WSe 2 , Lin et al showed strong electron correlation within the moiré flat band, which stabilizes insulating states at both quarter and half filling, and the spin-orbit coupling drives the Mott-like insulator into ferromagnetism.…”

“…[129,[152][153][154][155][156] Twisting graphene from a 2D-TMD in a 2D-TMD/graphene heterostructure can enhance the valley Zeeman and Rashba effects, [129,152] as well as the charge-to-spin conversion efficiency. [153,154] By tailoring the atomic interface between twisted bilayer graphene and WSe 2 , Lin et al showed strong electron correlation within the moiré flat band, which stabilizes insulating states at both quarter and half filling, and the spin-orbit coupling drives the Mott-like insulator into ferromagnetism. [155] In addition to the magnetic proximity and charge transfer effects, twisting adds an interesting experimental knob to tune the magnetic and magneto-optic functionalities of 2D-TMDs for spintronics and valleytronics applications.…”

Accelerated Data-Driven Discovery and Screening of Two-Dimensional Magnets Using Graph Neural Networks

“…Another important long-standing challenge is the realization of semiconducting magnets with critical temperatures above room temperature . Additionally, many 2D magnets exhibit interesting quantum phenomena such as superconductivity, spin liquid states, , and topological phases. − Consequently, this class of materials presents itself as a playground for quantum phenomena and strongly correlated effects, in addition to its numerous potential applications. As a result, many studies have been devoted to high-throughput and ML approaches to discover new 2D magnets.…”