Measurements of the complex dielectric permittivity in nominally pure ${\mathrm{SrTiO}}_3$ are reported for frequencies ${10}^{\mathrm{-}3}$ Hz≤ν≤${10}^8$ Hz and temperatures 0.1 K≤T≤300 K. The experiments reveal relaxation phenomena similar to those reported from elastic measurements. The onset of constant loss below 50 K and a low-temperature relaxation reveals characteristic features of a tunneling motion. These phenomena can be interpreted to be characteristic of a quantum phase transition into a coherent quantum state.

DOI:https://doi.org/10.1103/PhysRevB.50.601