Doped carbon nanotubes as a model system of biased graphene
  Albeit difficult to access experimentally, the density of states (DOS) is a key parameter in solid state systems which governs several important phenomena including transport, magnetism, thermal, and thermoelectric properties. We study DOS in an ensemble of potassium intercalated single-wall carbon nanotubes (SWCNT) and show using electron spin resonance spectroscopy that a sizeable number of electron states are present, which gives rise to a Fermi-liquid behavior in this material. A comparison between theoretical and the experimental DOS indicates that it does not display significant correlation effects, even though the pristine nanotube material shows a Luttinger-liquid behavior. We argue that the carbon nanotube ensemble essentially maps out the whole Brillouin zone of graphene thus it acts as a model system of biased graphene. 
P. Szirmai, B. G. M\'arkus, B. D\'ora, G. F\'abi\'an, J. Koltai, V.   Z\'olyomi, J. K\"urti, B. N\'afr\'adi, L. Forr\'o, T. ...
cond-mat.str-el cond-mat.mes-hall