Optical phonon contribution to the thermal conductivity of a quantum paraelectric

Abstract

Motivated by recent experimental findings, we study the contribution of a quantum critical optical phonon branch to the thermal conductivity of a paraelectric system. We consider the proximity of the optical phonon branch to transverse acoustic phonon branch and calculate its contribution to the thermal conductivity within the Kubo formalism. We find a low temperature power law dependence of the thermal conductivity as T α , with 1 < α < 2, (lower than T 3 behavior) due to optical phonons near the quantum critical point. This result is in accord with the experimental findings and indicates the importance of quantum fluctuations in the thermal conduction in these materials.

Phonon drag thermal Hall effect in metallic strontium titanate

“…This suggests a link between the amplitude of κ xy and the presence of ferroelectric fluctuations. Note that in 18 O-enriched strontium titanate [9], most 16 O atoms were substituted and the 20 K peak in κ xx is still present, in contrast to what is seen here. Yet, κ xy was similarly damped, ruling out that κ xy is simply more sensitive to disorder.…”

“…A previous study on the effect of 18 O substitution on the thermal Hall effect in strontium titanate [9] found a decrease of comparable magnitude. Substituting Sr by Ca [24,26] and substituting 16 O with 18 O [21,36] both stabilize a ferroelectric order, modify the superconducting dome and generate a polar metal. In both cases, the large κ xy of the quantum paraelectric solid is drastically suppressed with the stabilization of the ferroelectric order.…”

“…In strontium titanate, a non-magnetic insulator [8], the phononic origin of the THE [5,9] is uncontested. Theoretical scenarios [10][11][12][13][14][15][16] have been proposed to explain how phonons can generate a transverse thermal gradient on top of the longitudinal one.…”

Phonon drag thermal Hall effect in metallic strontium titanate

“…In strontium titanate, a nonmagnetic insulator ( 8 ), the phononic origin of the THE ( 5 , 9 ), is uncontested. Theoretical scenarios ( 10 – 16 ) have been proposed to explain how phonons can generate a transverse thermal gradient on top of the longitudinal one.…”