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★2014年5月29日(木) 16:20より
場 所： 理学部313教室
講演者： Derwyn Rowlands 博士(同済大学理工学部（中国 上海）)
講演題名：「Disappearance of the Dirac cone in silicene: "alloy-analogy" revisited」
講演概要：
Silicene is a silicon-based material which has only been recently experimentally-realized. Like carbon-based graphene, it has a 2D structure which gives rise to its unusual and potentially important properties. In order to design new electronic devices using silicene, it is essential to know how its electronic properties are affected by its interaction with the substrate on which it is grown. In particular, recent experimental investigations have given conflicting results as to whether the 2D graphene-like Dirac fermion properties are preserved. In order to investigate this important issue, we study the role played by an electric field which could be induced perpendicular to the Si plane when silicene is grown on a substrate such as Ag (111) as suggested by line-profile STM measurements. By describing the effect of the field using the 2D ionic Hubbard model on the honeycomb lattice, we make an "alloy analogy" and apply the coherent potential approximation (CPA) to the system. The calculations reveal symmetry-breaking by a charge density wave induced by the electric field which causes the silicene structure to lose its Dirac fermion characteristics, thus providing a simple mechanism for the disappearance of the Dirac cone.
★2014年4月25日(金) 16:20より
場 所： 理学部313教室
講演者： 坂井 典佑 先生 (東京工業大学名誉教授)
講演題名：「ヒッグス相のソリトン 〜素粒子の余剰次元模型とソリトン〜」
講演概要：
ソリトンは場の方程式の解として得られ，時空が４次元以上の高次元であるとする余剰次元模型を構築する上で，重要な役割を果たす．超伝導現象のようにゲージ対称性が破れる場合をヒッグス相と呼ぶ．この場合に生じるドメーンウォールやボーテックスなどのソリトンの研究の現状と最近の発展を述べる．
