what is Brillouin zone and K point?
The Brillouin zone is a fundamental concept in solid state physics. I'd recommend to better consult an introductory book on that topic, e.g. Mermin/Ashcroft or Kittel. Basically, it is a unit cell in reciprocal space. There are points of different symmetry in that space/cell, which are usually named by capital letters. As you seem to be interested in graphene, the K point is the point where the conduction and the valence band touch. The geometry of the surfaces around that point is locally conical. As the bands touch there, an excitation of an electron costs arbitrarily low energy whence the electrons behave as if being effectively massless. Hence the large recent interest in that material.
oh! thank a lot!!
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