日本原子力研究開発機構 (JAEA) / 量子ビーム応用研究部門
放射光科学研究ユニット / 放射光量子シミュレーショングループ
|Date and time:||27th May (Tue.) 16:00〜|
|Place:||SPring-8, "HOUKOUKAN" seminar room|
|Title:||Energy Gap and Averaged Inversion Symmetry of Tight-Binding Electrons on Generalized Honeycomb Lattice|
|講演者:||岸木敬太 氏 (熊本大学)|
|Speaker:||Prof. Keita Kishigi (Kumamoto University)|
The realization of ``massless Dirac fermions'' in graphene and the organic conductor α-(BEDT-TTF)2I3 attracts a lot of interest recently. The electron band structure of graphene can be understood using a tight-binding model on a honeycomb lattice[3,4]. One of the natural questions is what is the condition for the zero gap. Therefore, We study the condition to open a finite gap for the tight-binding electrons on an extended honeycomb lattice with the next-nearest-neighbor transfer integrals t2a, t2b, t2c, t2d, t2e and t2f, where t2a, t2b and t2c are transfer integrals between the sublattice A and t2d, t2e and t2f are transfer integrals between the sublattice B, and on-site potentials (εA and εB). If the system has the inversion symmetry in this model, i.e., the sublattices A and B have the same on-site potential (εA = εB), the gap is zero. We find that although the finite gap is generally opened by inversion-symmetry breaking, the gap remains zero if the averaged inversion symmetry, which is defined as the sum of the transfer integrals and the on-site potentials of the sublattices are the same (t2a + t2b + t2c + εA = t2d + t2e + t2f + εB), is conserved.