In quantum Hall states, which appear in two-dimensional systems under perpendicular magnetic field, current flows along sample edge. The edge channels provide unique one-dimensional systems to perform a variety of quantum transport experiments. Edge magnetoplasmons (EMPs) are collective charge excitations in the edge channels. Investigation of EMP properties, in particular, the decay mechanism is essential to obtain robust quantum effects in such systems. In this work, we show the dispersion relation and dissipation mechanisms of EMPs in graphene [1].

We prepared graphene by thermal decomposition of SiC. The samples used have disk shaped graphene. High-frequency transmission between two electrodes, which couple to graphene only capacitively, was investigated in frequency and time domains [Fig. 1(a)]. The dispersion relation of EMPs obtained by the frequency-domain measurement is nonlinear due to carrier interactions [Fig. 1(b)]. The velocity, which corresponds to the slope of the dispersion relation, is 1.7×10⁶ m/s for smaller wave number, consistent with that obtained by time-of-flight measurement [2]. This value is larger than the Fermi velocity in graphene (10⁶ m/s), demonstrating that charges propagate in collective modes, that is, EMPs. The EMP decay time is directly obtained by the time-domain measurement [Fig. 1(c)]. From its frequency and temperature dependence, EMP dissipations are found to be caused by capacitive and resistive couplings to localized states in the bulk graphene. We suggest that, owing to the linear band structure and the strong edge confinement, EMP dissipation in graphene can be lower than that in GaAs systems. Our results encourage using graphene for quantum transport experiments and plasmonic applications.