Axionic instability near topological quantum phase transition

Recently, axion electrodynamics in topological materials is one of the hot topics in condensed matter physics[1-3]. In~particular,~it has been pointed out that axion electrodynamics exhibits instability with~exotic electromagnetic response in~the presence of background~electric fields [2].~~In the presentation, we discuss~the instability due to dynamical axion field near a topological phase transition, where~the axion~field may have a large fluctuation decreasing the critical~electric field of the instability.~We report the electro-magnetic~response of the axion field~using two different model Hamiltonians.\\ \\ $[1]$ X.-L. Qi $\backslash $textit\textbraceleft et al.\textbraceright , Phys. Rev. B $\backslash $textbf\textbraceleft 78\textbraceright , 195424 (2008). \newline [2] R. Li $\backslash $textit\textbraceleft et al.\textbraceright , Nat. Phys. $\backslash $textbf\textbraceleft 6\textbraceright , 284 (2010). \newline [3] H. Ooguri $\backslash $textit\textbraceleft et al.\textbraceright , Phys. Rev. Lett. $\backslash $textbf\textbraceleft 108\textbraceright , 161803 (2012).