Temperature-induced surface phonon polaritons dissipation in perovskite SrTiO₃

Perovskite SrTiO₃ has emerged as a relevant technological material for nano-photonics that confines light to subdiffraction geometry with remarkably wide spectral tunability. Yet, the influence of lattice vibrations on its surface phonon polaritons (SPhPs) and localized surface phonon resonances (LSPhRs) receives little attention, and the underlying physics still remains elusive. Here, we apply spectroscopic ellipsometry (SE) experiments and multiscale simulations spanning from first-principles to finite-difference time-domain (FDTD), and investigate the temperature influence on infrared dielectric functions, SPhPs and LSPhRs of SrTiO₃. SE measurements find that the width of the Reststrahlen band lying between transverse and longitudinal oxygen-related optical phonons changes slightly, but infrared dielectric functions vary significantly as temperature increases. First-principles calculations confirm the coupling of the motion of oxygen atoms to incident photons, forming quasiparticles of SPhPs. FDTD simulations show that strong LSPhRs exist at 250 K in the SrTiO₃ nanodisks but dissipate as lattice vibration strengthens, mainly due to the reduced phonon relaxation lifetime. This work reveals the underlying physics of temperature influence on SPhPs and LSPhRs of SrTiO₃ and helps explore its potential applications as photonic resonators at high temperatures.