title: Spin Lifetimes Exceeding 12 ns in Graphene Nonlocal Spin Valve Devices.
abstract: We show spin lifetimes of 12.6 ns and spin diffusion lengths as long as 30.5 μm in single layer graphene nonlocal spin transport devices at room temperature. This is accomplished by the fabrication of Co/MgO-electrodes on a Si/SiO2 substrate and the subsequent dry transfer of a graphene-hBN-stack on top of this electrode structure where a large hBN flake is needed in order to diminish the ingress of solvents along the hBN-to-substrate interface. Interestingly, long spin lifetimes are observed despite the fact that both conductive scanning force microscopy and contact resistance measurements reveal the existence of conducting pinholes throughout the MgO spin injection/detection barriers. Compared to previous devices, we observe an enhancement of the spin lifetime in single layer graphene by a factor of 6. We demonstrate that the spin lifetime does not depend on the contact resistance area products when comparing all bottom-up devices indicating that spin absorption at the contacts is not the predominant source for spin dephasing.
authors.affiliation: 2nd Institute of Physics and JARA-FIT, RWTH Aachen University , 52074 Aachen, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Drögeler
authors.affiliation: 2nd Institute of Physics and JARA-FIT, RWTH Aachen University , 52074 Aachen, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Franzen
authors.affiliation: 2nd Institute of Physics and JARA-FIT, RWTH Aachen University , 52074 Aachen, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Volmer
authors.affiliation: 2nd Institute of Physics and JARA-FIT, RWTH Aachen University , 52074 Aachen, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Pohlmann
authors.affiliation: 2nd Institute of Physics and JARA-FIT, RWTH Aachen University , 52074 Aachen, Germany.
authors.forename: Luca
authors.initials: L
authors.lastname: Banszerus
authors.affiliation: 2nd Institute of Physics and JARA-FIT, RWTH Aachen University , 52074 Aachen, Germany.
authors.forename: Maik
authors.initials: M
authors.lastname: Wolter
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: 2nd Institute of Physics and JARA-FIT, RWTH Aachen University , 52074 Aachen, Germany.|Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Stampfer
authors.affiliation: 2nd Institute of Physics and JARA-FIT, RWTH Aachen University , 52074 Aachen, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Beschoten
keywords: Graphene; Hanle spin precession; boron nitride; contact-induced spin dephasing; pinholes; spin transport