Unit cell dependence of optical matrix elements in tight-binding theory: The case of zigzag graphene nanoribbons

详细信息    查看全文

• 作者：Kondayya Gundra ; ^a ; ^{naiduk@barc.gov.in"" rel=""nofollow} ; Alok Shukla^a ; ^{shukla@iitb.ac.in"" rel=""nofollow}
• 关键词：Tight-binding theory ; Momentum matrix elements ; Optical properties ; Graphene nanoribbons
• 刊名：Physica B
• 出版年：2011
• 出版时间：1 October 2011
• 年：2011
• 卷：406
• 期：19
• 页码：3538-3543
• 全文大小：386 K

文摘

In the tight-binding theory, momentum matrix elements (MMEs) needed to calculate the optical properties are normally computed using a formulation based on the gradient of the Hamiltonian in the k space. We demonstrate the inadequacy of this formulation by considering the case of zigzag graphene nanoribbons. We show that one obtains wrong values of MMEs, in violation of the well-known selection rules, if the unit cell chosen in the calculations does not incorporate the symmetries of the bulk. This is in spite of the fact that the band structure is insensitive to the choice of the unit cell. We substantiate our results based on group-theoretic arguments. Our observations will open an avenue for proper formulation of MMEs.