Second sound in SrTiO3.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Thermodynamics

Background:

• Strontium titanate (SrTiO3) exhibits complex phonon dynamics.
• Understanding heat transport mechanisms in dielectric crystals is crucial for thermal management applications.

Purpose of the Study:

• To investigate collective phonon excitations in SrTiO3 using low-frequency light scattering.
• To develop a theoretical model for phonon gas applicable beyond local thermal equilibrium.
• To determine the temperature dependence of relaxation times for phonon-momentum-conserving collisions.

Main Methods:

• Low-frequency light scattering experiments on SrTiO3.
• Application of extended thermodynamics for phonon gas.
• Construction of a theoretical spectral function valid under non-equilibrium conditions.

Main Results:

• The temperature dependence of tauN, the relaxation time for normal phonon processes, was determined.
• The analysis provides a theoretical framework for spectral functions beyond local thermal equilibrium.
• Evidence suggests that anomalous soundlike spectra in SrTiO3 are attributed to second sound.

Conclusions:

• Second sound, a wavelike heat propagation, explains the anomalous soundlike spectrum in SrTiO3.
• The study provides insights into non-equilibrium phonon hydrodynamics in dielectric materials.