第44回 原研・兵県大合同コロキウム

日時: 平成20年5月27日(火) 16:00〜
Date and time: 27th May (Tue.) 16:00〜
場所: SPring-8, 萌光館
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)
Abstract:

The realization of ``massless Dirac fermions'' in graphene[1] and the organic conductor α-(BEDT-TTF)2I3[2] 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.[5]