Van der Waals heterostructures have become a paradigm for designing new materials and devices in which specific functionalities can be tailored by combining the properties of the individual 2D layers. A single layer of transition-metal dichalcogenide (TMD) is an excellent complement to graphene (Gr) because the high quality of charge and spin transport in Gr is enriched with the large spin–orbit coupling of the TMD via the proximity effect. The controllable spin-valley coupling makes these heterostructures particularly attractive for spintronic and opto-valleytronic applications. In this work, we study spin precession in a monolayer MoSe2/Gr heterostructure and observe an unconventional, dramatic modulation of the spin signal, showing 1 order of magnitude longer lifetime of out-of-plane spins compared to that of in-plane spins (τ⊥ ≈ 40 ps and τ∥ ≈ 3.5 ps). This demonstration of a large spin lifetime anisotropy in TMD/Gr heterostructures, is a direct evidence of induced spin-valley coupling in Gr and provides an accessible route for manipulation of spin dynamics in Gr, interfaced with TMDs.

The proximity of a transition-metal dichalcogenide (TMD) to graphene imprints a rich spin texture in graphene and complements its high-quality charge/spin transport by inducing spin–orbit coupling (SOC). Rashba and valley-Zeeman SOCs are the origin of charge-to-spin conversion mechanisms such as the Rashba–Edelstein effect (REE) and spin Hall effect (SHE). In this work, we experimentally demonstrate for the first time charge-to-spin conversion due to the REE in a monolayer WS2-graphene van der Waals heterostructure. We measure the current-induced spin polarization up to room temperature and control it by a gate electric field. Our observation of the REE and the inverse of the effect (IREE) is accompanied by the SHE, which we discriminate by symmetry-resolved spin precession under oblique magnetic fields. These measurements also allow for the quantification of the efficiencies of charge-to-spin conversion by each of the two effects. These findings are a clear indication of induced Rashba and valley-Zeeman SOC in graphene that lead to the generation of spin accumulation and spin current without using ferromagnetic electrodes. These realizations have considerable significance for spintronic applications, providing accessible routes toward all-electrical spin generation and manipulation in two-dimensional materials.

These authors contributed equally to this work. The introduction and control of ferromagnetism in graphene opens up a range of new directions for fundamental and applied studies. Several approaches have been pursued so far, such as introduction of defects, functionalization with adatoms, and shaping of graphene into nanoribbons with well-defined zigzag edges. 1-6 A more robust and less invasive method utilizes the introduction of an exchange interaction by a ferromagnetic insulator (FMI) in proximity with graphene. 7-14Here we present a direct measurement of the exchange interaction in room temperature ferromagnetic graphene. We study the spin transport in exfoliated graphene on a yttriumiron-garnet (YIG) substrate where the observed spin precession clearly indicates the presence and strength of an exchange field that is an unambiguous evidence of induced ferromagnetism. We describe the results with a modified Bloch diffusion equation and extract an average exchange field of the order of 0.2 T. Further, we demonstrate that a proximity induced 2D ferromagnet can efficiently modulate a spin current by controlling the direction of the exchange field. These results can create a building block for magneticgate tuneable spin transport in one-atom-thick spintronic devices. 8,9

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A new two dimensional (2D) material-germanane-has been synthesised recently with promising electrical and optical properties. In this paper we report the first realisation of germanane fieldeffect transistors fabricated from multilayer single crystal flakes. Our germanane devices show transport in both electron and hole doped regimes with on/off current ratio of up to 10 5 (10 4 ) and carrier mobilities of 150 cm 2 (V • s) −1 (70 cm 2 (V • s) −1 ) at 77 K (room temperature). A significant enhancement of the device conductivity under illumination with 650 nm red laser is observed. Our results reveal ambipolar transport properties of germanane with great potential for (opto)electronics applications. LETTER RECEIVED

We experimentally study the effect of different scattering potentials on the flicker noise observed in graphene devices on silica substrates. The noise in nominally identical devices is seen to behave in two distinct ways as a function of carrier concentration, changing either monotonically or nonmonotonically. We attribute this to the interplay between long-and short-range scattering mechanisms. Water is found to significantly enhance the noise magnitude and change the type of the noise behaviour. By using a simple model, we show that water is a source of long-range scattering.PACS numbers: 72.10. Fk, 72.70.+m, 72.80.Vp, 73.20.Hb The phenomenon of flicker noise (also known as 1/f noise) has been intensively studied in semiconductor structures 1,2 . In Si MOSFETs it is ascribed to the random tunneling of electrons between the conducting channel and nearby impurity states, and measurements of the noise provide information about such states and their effect on the conduction 2 . A promising material to supercede silicon in future nanoelectronics is graphene 3 . Electrical conduction through graphene is limited by various scattering mechanisms, which cannot be distinguished by their effect on the electronic transport. For instance, the linear relation between graphene conductivity and carrier concentration was initially attributed to scattering by Coulomb impurities 4 . Later, it was realised that other scatterers, such as vacancies and ripples, produce nearly identical dependences 5,6 . Recent measurements of flicker noise in monolayer graphene have shown that this noise is sensitive to the method of fabrication of the device 7-9 , which suggests that it results from several distinct sources of scattering. In this work, we measure the flicker noise in graphene on top of a SiO 2 substrate and demonstrate that it is possible to use such measurements as a sensitive tool to distinguish between shortand long-range scattering mechanisms. We identify water molecules as a source of long-range scattering and show that their removal by thermal annealing has a dramatic effect on the flicker noise.Graphene transistors were prepared by mechanical exfoliation of graphene flakes onto n + Si/SiO 2 wafers with oxide thickness 300 nm. Multiple Au/Cr contacts were made to each flake. The flakes had dimensions ranging from 1 to 4 µm in width and from 5 to 22 µm in length and were verified to be monolayers by means of Raman spectroscopy 10 and measurement of plateau positions in the quantum Hall regime 11 . The concentration of carriers was tuned by applying gate voltage, V G , between the substrate and the graphene. Four-terminal measurements of the resistance were carried out at 300 K either in an inert He atmosphere or in vacuum. A total of 8 samples, named S1 to S8, were studied in detail. Samples S4-S8 were measured both before and after annealing (designated here by an asterisk) at a temperature of 140• C for about 1 hour. The low-frequency noise ( 200 Hz) was measured using both a spectrum analyser and a lock-in amplifier. T...

Electron transport nonlocality in monolayer graphene modified with hydrogen silsesquioxane polymerization Kaverzin, A. A.; van Wees, B. J. A number of practical and fundamental applications of graphene requires modification of some of its properties. In this paper we study the effect of polymerization of a hydrogen silsesquioxane film on top of monolayer graphene with the intent to increase the strength of the spin-orbit interaction. The measured nonlocal resistances R NL were found to be up to 700 , significantly exceeding the expected contribution from conventional Ohmic currents. The R NL dependence on the channel length resembles exponential decay with a characteristic length of λ 500 nm that is close to the spin-relaxation length in graphene reported elsewhere. The sensitivity of the measured effect to the electron-beam exposure was shown to decrease with an increased level of the surface contamination. However, no modulation of the effect is observed when an in-plane magnetic field is applied. This implies that a spin Hall model fails to explain the observed phenomenon and an alternative interpretation is required.

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