Electronic spin transport and spin precession in single graphene layers at room temperature

Abstract

Electronic transport in single or a few layers of graphene is the subject of intense interest at present. The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states, has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport, supercurrent transport has also been observed. Graphene might also be a promising material for spintronics and related applications, such as the realization of spin qubits, owing to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. Here we report the observation of spin transport, as well as Larmor spin precession, over micrometre-scale distances in single graphene layers. The 'non-local' spin valve geometry was used in these experiments, employing four-terminal contact geometries with ferromagnetic cobalt electrodes making contact with the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals that reflect the magnetization direction of all four electrodes, indicating that spin coherence extends underneath all of the contacts. No significant changes in the spin signals occur between 4.2 K, 77 K and room temperature. We extract a spin relaxation length between 1.5 and 2 mum at room temperature, only weakly dependent on charge density. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around ten per cent.

Electronic and Magnetic Properties of Partially Open Carbon Nanotubes

“…Among them, chemical functionalization/doping and the application of external eletric/magnetic fields are known as being practically viable approaches to tailoring the electrical properties of CNTs 5,7,12,13,14,15 . In general, carbon-based systems are promising candidates for spin-based applications such as spin-qubits and spintronics 11,12,16,17,18,19,20 ; they are believed to have exceptionally long spin coherence times because of the absence of the nuclear spin in the carbon atom and very weak spin-orbit interactions. Therefore, in addition to their unique electrical properties, designing and modulating the spin injection and spin transport in CNTs have drawn heightened attention.…”

Long Spin Relaxation Times in Wafer Scale Epitaxial Graphene on SiC(0001)

“…1 Recent experiments show an increase of τ S to τ S ≈ 0.5 ns in eSLG at RT 2,3 and τ S ≈ 1 ns at T = 4 K. 3 Measurements on bilayer graphene (BLG) show even higher spin relaxation times of up to a few nanoseconds at low temperature. 3,4 At the same time, a study on few-layer graphene (FLG) showed an enhancement of τ S with increasing number of layers, which is attributed to the screening of external scattering potentials.…”

Tuning the Electronic Structure of Graphene by an Organic Molecule

“…The large spin-polarization of charge carriers at the Fermi level could be useful for graphene-based spintronic devices, which is expected to have long spin relaxation length. 32 Next, we consider higher coverage of TCNE molecules on graphene. Here, a 2(3) 1/2 × 3 supercell containing 24 carbon atoms per graphene layer and 1 TCNE was used.…”