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Answer:
The structure of graphene consists of two different
types of lattice sites. Vectors pointing to nearest
neighbours for one set of lattice site (say A) are
rotated by 60 degrees compared the corresponding
vectors for the other set (say B). Every unit cell
(which repeat by translation over the lattice) has
one site of type A and another of type B. The
wavefunctions for A and B sites, when combined
together as a two component vector, can be treated
as two components of a spin-1/2 particle. So the
A/B label is called pseudospin, while ordinary
spin is generally labeled up/down.
By:
Prof. Apoorva D Patel Date:
2013-03-22
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