Anharmonic Eigenvectors and Acoustic Phonon Disappearance in Quantum Paraelectric SrTiO_{3}.

摘要: Pronounced anomalies in the SrTiO_{3} dynamical structure factor, S(Q,E), including disappearance of acoustic phonon branches at low temperatures, were uncovered with inelastic neutron scattering (INS) and simulations. The striking effect reflects anharmonic couplings between optic phonons incipient ferroelectric instability near quantum critical point. It is rationalized using a first-principles renormalized approach, pointing to nonlinear Ti-O hybridization causing unusual changes real-space eigenvectors, frequencies, group velocities, phase space. Our method general establishes how T dependences beyond harmonic regime, assessed by INS mapping large reciprocal-space volumes, provide insights into atomic dynamics transitions.