The halon is a special state of an impurity in a gapless environment. The hallmark of the halon physics is that a well-defined integer charge of the dressed impurity gets fractionalized into two parts: a microscopic core with a fractionalized charge and a large halo carrying a complementary charge. We discuss three systems demonstrating the haloneffect: i) A local potential well in a two-dimensional superfluid--Mott-insulator quantum critical environment traps 1/2 particle/hole. ii) A heavy polaron in a Fermi gas carries a macroscopic screening cloud with a fractionalized charge. iii) A three-dimensional (type-II) superconductor at the critical temperature demonstrates a critical Meissner effect.
Kun Chen received his Bachelor degree in physics from USTC in 2011. He received PhD degree from USTC in 2016 and from UMass Amherst in 2018. Since 2017, Kun Chen started as Simons Postdoctoral Fellow in Rutgers University, New Jersey. His main research interest is the development of novel field-theoretic and numerical approaches and their applications in correlated electrons and ultra-cold atoms.