講演者:Sung G. Chung 氏(Western Michigan University) 日時:6月 17日(金) 午後4時30分から 場所: 青山学院大学 理工学部(相模原キャンパス)L棟6階 L603室 題目: 「Entanglement perturbation theory for quasi-1D quantum systems」 要旨:  Quasi 1D systems such as spin-tubes, graphene nano-ribbons and carbon nano-tubes are interesting both theoretically and practically. Theoretically, various 1D fermions with long-range interactions and hopping have been studied as toy models for ferromagnetism and superconductivity. Practically, quasi 1D systems have been under an extensive study for their possible devise applications. We here develop Entanglement Perturbation Theory (EPT) for macroscopic quasi-1D systems, considering as a prototypical system, the spin 1/2 Heisenberg chain with ferromagnetic nearest neighbor and antiferromagnetic next nearest neighbor interactions with an easy-plane anisotropy, equivalent to a coupled 2 spin chains called the zigzag chain. Our finding is as follows. (1) EPT gives a converging, and hence exact phase diagram, giving exact order parameters of Neel and dimer phases for the entire parameter space along the Lifshitz line. (2) The Bosonization method based on the perturbative sine-Gordon analysis is incorrect in deeply frustrative regime. (3) iTEBD, a variant of DMRG, even with a large entanglement 300, is not as accurate as EPT with 80. ---------------------------------