The investigation of the electronic properties of graphene (single hexagonal layer of carbon atoms) has attracted a renewed interest after the development of recent techniques which permit to produce and manage single-layer (and also multilayer) samples of this materials. Nowadays truly atomic single-layer isolated samples are available as well as epitaxially grown graphene on substrates.
using optical measurements. Related with this issue is also the observation of a gap at the chemical potential in doped samples. Of fundamental relevance from the technological point of view it is also the control of transport mechanisms. Graphenes are indeed systems with extremely high mobility µ ~ m2/Vs, which is limited by the presence of different scattering channels. Understanding and controlling such scattering channels appears thus of the highest importance for optimising transport properties. Within this context, debated open issues which still require a satisfactory understanding are: the report of a minimal conductance at the Dirac point which is 3-4 times larger than the predicted universal one; the linear dependence of the conductivity on the gate voltage Vg and hence on the carrier density n; the low temperature behavior T < TBGin doped samples; the doping dependence of the linear temperature behavior of for T > TBG.
Researchers of ISC-Sapienza are currently working on this field. In our activity investigated many electronic, transport and spectroscopy properties of single layer and bilayered graphene. We studied for instance the dependence of the optical sum-rule in bilayer systems as function of doping and we showed that the sum-rule is only weakly by the opening of the gap induced by he gate-voltage. We have also analyze the angle-resolved photoemission data in epitaxially grown graphene which show a opening of the gap at the Dirac point, whose nature is not clear system. Different interpretations of such feature have been advanced. In this context we proposed a phenomenological model, based on the opening of a massless gap, which permits to explain several controversial issues.We have also investigatd the robustness of the Boltzmann theory of transport in doped graphene, in particular for what concerns the relevance of the transport angular 1-cos?. We have shown that, although the multiband chiral character questions the straightforward applicability of the Boltzmann theory, transport properties are still characterized by such angular factor which stems from the strict relation between scattering in the momentum and the chiral space.
People: L. Benfatto, E. Cappelluti.
– L.Benfatto, S.G.Sharapov, J.P.Carbotte, “Robustness of the optical-conductivity sum rule in Bilayer Graphene“, 125422
– L. Benfatto and E. Cappelluti, “Spectroscopic signatures of massless gap opening in graphene“
– E. Cappelluti and L. Benfatto, “Vertex renormalization in DC conductivity of doped chiral graphene“, arXiv:0809.4215v1 [cond-mat.mes-hall] (2008).