Intercalated Graphene Bilayers: London Penetration Depth Study

K.M. Skoczylasa, A.E. Auguścikb, R. Szczęśniakb aJan Długosz University in Częstochowa, Institute of Physics, al. Armii Krajowej 13/15, 42-200 Częstochowa, Poland bCzęstochowa University of Technology, Institute of Physics, al. Armii Krajowej 19, 42-200 Częstochowa, Poland

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The Eliashberg strong-coupling theory of superconductivity has been used to obtain the London penetration depth functions (λL) for superconducting doped graphene bilayers. Analyzed systems can be described by the following chemical formula: C6XC6, where X is the dopant belonging to the I or II group (either K, Rb, or Ca, Sr). Our recent work on these systems show the capability of superconducting state occurrence with the highest critical temperature (Tc) for calcium intercalation (Tc=14.56 K). This result adds to the very long list of eligible characteristics of doped two-dimensional graphene sheet. This work comprises the capability of C6XC6 systems to attenuate the magnetic vortices arising inside the structure of the superconductor under the application of an external magnetic field or electric current. We note the highest λL (at T=0 K) values for the case of calcium intercalation which holds the highest Tc. However, we also observe that rubidium insertion does not lead to higher λL(0) value than potassium and strontium intercalation (Tc=8.67 K and 8.74 K, respectively) with the lowest critical temperature (Tc=5.47 K). Additionally, the course of (λL(0)/λL(T))2 function can be compared to the BCS theory predictions which lead to the conclusion of C6XC6 group being conventional electron-phonon superconductors with properties beyond the BCS theory.

DOI:10.12693/APhysPolA.138.178 topics: superconductivity, two-dimensional, graphene, Eliashberg theory, thermodynamic properties