Lattice and polarizability mediated spin activity in EuTiO₃

EuTiO_3 is shown to exhibit novel strong spin-charge-lattice coupling deep in the paramagnetic phase. Its existence is evidenced by an, until now, unknown response of the paramagnetic susceptibility at temperatures exceeding the structural phase transition temperature T_S = 282K. The "extra" features in the susceptibility follow the rotational soft zone boundary mode temperature dependence above and below T_S. The theoretical modeling consistently reproduces this behavior and provides reasoning for the stabilization of the soft optic mode other than quantum fluctuations.