Title: Exotic symmetry-breaking phases from constrained dynamics
Speaker: Prof. Peng Ye (Sun Yat-Sen University)
Abstract: While the traditional symmetry-breaking orders (SSB), e.g., superfluiditity, can be theoretically obtained by considering a Mexican hat that spontaneously breaks global symmetry, e.g., U(1) in the ground states, in this talk, I will introduce a new type of SSB orders in which the broken symmetry is called "higher-rank symmetry" that transforms boson operators in a way that the group parameters are allowed to depend on space coordinates while the Hamiltonian still keeps invariant without the need of gauge degrees of freedom. We consider concrete examples dubbed “fractonic superfluids” in which higher rank U(1) symmetry is spontaneously broken. The associated conserved quantities are both total particle number and total higher moments (e.g., dipoles, angular moments, quadrupoles) that substantially constrain the low-energy dynamics. We construct minimal Hamiltonians, and study many properties of these many-body systems, e.g., Noether currents, GP equations, ODLRO against quantum fluctuations at various dimensions, and symmetry defects as well as their thermally activated proliferation that leads to hierarchical KT transitions. In addition to our systematic concrete model studies, more recently, there have been exciting updates in the community, including general discussions on Mermin-Wagner theorem and SSB of higher moment conservation in high energy physics, and realization on Hubbard models.
References: arXiv:1911.02876. Phys. Rev. Research 2, 023267 (2020). arXiv:2010.03261. Phys. Rev. Research 3, 013226 (2021). arXiv:2104.03237. Phys. Rev. Research 3, 043176 (2021). arXiv:2201.08597 arXiv:2203.06984. Chin. Phys. Lett. 39, 057101 (2022).