Absence of hyperfine effects in 13C-graphene spin-valve devices

Ivan Vera Marun, M Wojtaszek, I J Vera-Marun, E Whiteway, M Hilke, B J van Wees

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    Abstract

    The carbon isotope 13{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}13{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater}C, in contrast to 12{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}12{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater}C, possesses a nuclear magnetic moment and can induce electron spin dephasing in graphene. This effect is usually neglected due to the low abundance of 13{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}13{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater}C in natural carbon allotropes (???{\textless}math{\textgreater}{\textless}mo{\textgreater}???{\textless}/mo{\textgreater}{\textless}/math{\textgreater}1\%). Chemical vapor deposition (CVD) allows for artificial synthesis of graphene solely from a 13{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}13{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater}C precursor, potentially amplifying the influence of the nuclear magnetic moments. In this work we study the effect of hyperfine interactions in pure 13{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}13{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater}C-graphene on its spin transport properties. Using Hanle precession measurements we determine the spin relaxation time and observe a weak increase of ??s{\textless}math{\textgreater}{\textless}msub{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}??{\textless}/mi{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}s{\textless}/mi{\textgreater}{\textless}/msub{\textgreater}{\textless}/math{\textgreater} with doping and a weak change of ??s{\textless}math{\textgreater}{\textless}msub{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}??{\textless}/mi{\textgreater}{\textless}mi \_moz-math-font-style="italic"{\textgreater}s{\textless}/mi{\textgreater}{\textless}/msub{\textgreater}{\textless}/math{\textgreater} with temperature, as in natural graphene. For comparison we study spin transport in pure 12{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}12{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater}C-graphene, also synthesized by CVD, and observe similar spin relaxation properties. As the signatures of hyperfine effects can be better resolved in oblique spin-valve and Hanle configurations, we use finite-element modeling to emulate oblique signals in the presence of a hyperfine magnetic field for typical graphene properties. Unlike in the case of GaAs, hyperfine interactions with 13{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}13{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater}C nuclei influence electron spin transport only very weakly, even for a fully polarized nuclear system. Also, in the measurements of the oblique spin-valve and Hanle effects no hyperfine features could be resolved. This work experimentally confirms the weak character of hyperfine interactions and the negligible role of 13{\textless}math{\textgreater}{\textless}msup{\textgreater}{\textless}mrow{\textgreater}{\textless}/mrow{\textgreater}{\textless}mn{\textgreater}13{\textless}/mn{\textgreater}{\textless}/msup{\textgreater}{\textless}/math{\textgreater}C atoms in the spin dephasing processes in graphene.
    Original languageEnglish
    JournalPhysical Review B
    Volume89
    Issue number3
    DOIs
    Publication statusPublished - Jan 2014

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