아래와 같이 세미나를 개최하오니 많이 참석해 주시기 바랍니다. 아 래 제목: An Ideal Mean-Field Transition in a Driven Interacting System 연사: 허 명 선 박사 (서울대학교) 일시: 2009년 10월 15일(목) 16:00 장소: 기초과학연구소 세미나실(31317호) 초록: Mean-field approach has been instrumental for developing an insight into critical phenomena. However, close to the phase transition point the mean field approximation usually breaks down. Here we report an observation of an ideal mean-field symmetry breaking transition and the associated critical behavior. The transition occurs in an atomic cloud confined in a periodically modulated magneto-optical trap once the number of atoms reaches a critical value. In the symmetric phase, the atoms equally occupy two parametrically excited vibrational states with opposite phase. As a result of the transition, the state occupations become different. This is symmetry breaking in time rather than in space. It is due to the interatomic interaction and is mediated by nonequilibrium fluctuations. The results demonstrate that a mean-field transition can occur in a many-body system and that the notion of discrete symmetry breaking transitions can be extended to the time domain.