【报告题目】Excitonic semimetal-insulator quantum criticality in Dirac fermion systems
【报告摘要】The low-energy excitations of graphene and other similar semimetals are massless Dirac fermions. The density of states vanishes at the Fermi level, thus the Coulomb interaction is long-ranged and leads to a variety of unusual properties. When the Coulomb interaction is strong enough, a finite gap is opened due to excitonic pairing, which then drives a semimetal-insulator quantum phase transition. This scenario is a condensed-matter realization of dynamical chiral symmetry breaking, an important concept of particle physics. The system exhibits rich quantum critical phenomena near the semimetal-insulator quantum critical point. We study the excitonic insulating transition and the associated quantum criticality in a number of Dirac fermion systems, and discuss how to detect the theoretically predicted quantum critical phenomena.