Colossal permittivity induced by lattice mirror reflection symmetry breaking in Ba$_{7}$Ir$_{3}$O$_{13+x}$(0 $\le $x$\le $ 1.5) epitaxial thin films

Materials with colossal permittivity (CP) at room temperature hold tremendous promise in modern microelectronics as well as high-energy-density storage applications. Despite several proposed mechanisms that lead torecent discoveries of a series of new CP materials such as Nb, In co-doped TiO$_{2}$ and CaCu$_{3}$Ti$_{4}$O$_{12}$ ceramics, it is imperative to find other approaches which can further guide the search for new CP materials. In this talk, we will demonstrate a new mechanism for CP: the breaking of mirror reflection symmetry of lattice can cause CP. This mechanism was revealed in a new layered iridate Ba$_{7}$Ir$_{3}$O$_{13+x}$ (BIO) thin film we recently discovered. Structural characterization of BIO films show that its mirror reflection symmetry is broken along $b$-axis, but preserved along $a$- and $c$-axes. Dielectric property measurements of BIO films at room temperature show a CP (10$^{3}$-10$^{4})$ along the in-plane direction, but a much smaller permittivity (10- 20) along the $c$-axis, in the 10$^{2}$- 10$^{6}$ Hz frequency range. Such unusually large anisotropy in permittivity testifies to the significant role of the structural in-plane mirror reflection symmetry breaking in inducing CP.