Thermal transport and phonon hydrodynamics in strontium titanate

TL;DR

This study investigates thermal conductivity and phonon hydrodynamics in strontium titanate, revealing Poiseuille flow of phonons in undoped samples and the impact of doping on heat transport across a wide temperature range.

Contribution

It provides experimental evidence of phonon hydrodynamics and Poiseuille flow in strontium titanate, highlighting how doping suppresses these effects and elucidating temperature-dependent thermal transport mechanisms.

Findings

Poiseuille flow observed in undoped SrTiO3 below its peak thermal conductivity.

Doping with Nb reduces lattice thermal conductivity and suppresses phonon hydrodynamics.

High-temperature thermal diffusivity inversely proportional to temperature, governed by sound velocity and Planckian time.

Abstract

We present a study of thermal conductivity, $\kappa$, in undoped and doped strontium titanate in a wide temperature range (2-400 K) and detecting different regimes of heat flow. In undoped SrTiO$_{3}$, $\kappa$ evolves faster than cubic with temperature below its peak and in a narrow temperature window. Such a behavior, previously observed in a handful of solids, has been attributed to a Poiseuille flow of phonons, expected to arise when momentum-conserving scattering events outweigh momentum-degrading ones. The effect disappears in presence of dopants. In SrTi$_{1-x}$Nb$_{x}$O$_{3}$, a significant reduction in lattice thermal conductivity starts below the temperature at which the average interdopant distance and the thermal wavelength of acoustic phonons become comparable. In the high-temperature regime, thermal diffusivity becomes proportional to the inverse of temperature, with a prefactor set by sound velocity and Planckian time ($\tau_{p}=\frac{\hbar}{k_{B}T}$).