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The phase diagram of iron-based superconductors consists of various electronic orders, including antiferromagnetic and symmetry related vestigial orders, which are highly entangled with superconductivity. In this talk, I will show the hidden Lie algebra among the various vestigial orders in iron-based superconductors. Because of the intertwined nature of these order parameters, the phase transition between the nematic and density C_4 phases exhibits an enhanced U(1) symmetry, despite its first-order nature. This enriched continuous symmetry gives rise to a Goldstone mode at the transition point and causes softening of susceptibilities in the nematic and charge sectors when the system is close to the transition. I will propose ways for probing these effects in experiments, and discuss the implications of our results for the superconductivity of iron-based systems.
Rong Yu is a professor at Department of Physics, Renmin University of China. He obtained his Ph.D. degree from University of Southern California in 2007. He was a postdoctoral research associate at University of Tennessee, Knoxville (2007–2009) and at Rice University (2009-2013). He has been working on theory of correlated electronic systems. Current main areas of his research includes superconductivity and correlation effects in iron-based superconductors, frustration and disorder effects in quantum magnets, and phase transitions in heavy fermion systems.