Observation of a universal donor-dependent vibrational mode in graphene.
Electron-phonon coupling and the emergence of superconductivity in intercalated graphite have been studied extensively. Yet, phonon-mediated superconductivity has never been observed in the 2D equivalent of these materials, doped monolayer graphene. Here we perform angle-resolved photoemission spectroscopy to try to find an electron donor for graphene that is capable of inducing strong electron-phonon coupling and superconductivity. We examine the electron donor species Cs, Rb, K, Na, Li, Ca and for each we determine the full electronic band structure, the Eliashberg function and the superconducting critical temperature Tc from the spectral function. An unexpected low-energy peak appears for all dopants with an energy and intensity that depend on the dopant atom. We show that this peak is the result of a dopant-related vibration. The low energy and high intensity of this peak are crucially important for achieving superconductivity, with Ca being the most promising candidate for realizing superconductivity in graphene.
1] IFW Dresden, P.O. Box 270116, Dresden D-01171, Germany [2] St Petersburg State University, Ulianovskaya 1, St Petersburg 198504, Russia.
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Fedorov
1] Faculty of Physics, University of Vienna, Strudlhofgasse 4, Vienna A-1090, Austria [2] Department of Materials Science, Moscow State University, Leninskiye Gory 1/3, Moscow 119992, Russia.
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Verbitskiy
1] IFW Dresden, P.O. Box 270116, Dresden D-01171, Germany [2] Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300, USA.
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Haberer
Elettra Sincrotrone Trieste, Strada Statale 14 km 163.5, Trieste 34149, Italy.
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Struzzi
Elettra Sincrotrone Trieste, Strada Statale 14 km 163.5, Trieste 34149, Italy.
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Petaccia
St Petersburg State University, Ulianovskaya 1, St Petersburg 198504, Russia.
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D
Usachov
St Petersburg State University, Ulianovskaya 1, St Petersburg 198504, Russia.
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Vilkov
1] St Petersburg State University, Ulianovskaya 1, St Petersburg 198504, Russia [2] Institut für Festkörperphysik, TU Dresden, Mommsenstrasse 13, Dresden D-01069, Germany.
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Vyalikh
IFW Dresden, P.O. Box 270116, Dresden D-01171, Germany.
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Fink
IFW Dresden, P.O. Box 270116, Dresden D-01171, Germany.
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Knupfer
IFW Dresden, P.O. Box 270116, Dresden D-01171, Germany.
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Büchner
1] IFW Dresden, P.O. Box 270116, Dresden D-01171, Germany [2] Faculty of Physics, University of Vienna, Strudlhofgasse 4, Vienna A-1090, Austria.
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Grüneis