Anomalous Glassy Thermal Conductivity in a Perovskite Bismuthate Induced by Structural Dynamic Instability

Area of Science:

• Materials Science
• Condensed Matter Physics

Background:

• Understanding thermal conductivity is crucial for designing new functional materials.
• Ultra-low thermal conductivity in pristine crystals presents a significant challenge.

Purpose of the Study:

• To investigate the thermal conductivity (κ(T)) of single-crystalline BaBiO3 over an extended temperature range (1.5-400 K).
• To elucidate the mechanisms responsible for the anomalous thermal transport properties observed in BaBiO3.

Main Methods:

• Experimental measurement of thermal conductivity κ(T) from 1.5 K to 400 K.
• Theoretical calculations incorporating three-phonon and isotope disorder scattering.
• Analysis of phonon scattering mechanisms, including potential contributions from tunneling two-level systems.

Main Results:

• Observed anomalous glass-like thermal conductivity with a T^2 dependence at low temperatures and a plateau from 20 K to 260 K.
• Measured room temperature κ ≈ 1.6 W m^-1 K^-1, consistent with calculations.
• Experimental κ(T) deviates from calculations below 300 K, indicating an additional scattering mechanism.

Conclusions:

• A tunneling two-level system associated with BiO6 octahedra rotation is proposed as the additional phonon scattering mechanism.
• This mechanism explains the suppressed thermal conductivity in BaBiO3 at lower temperatures.
• Findings have implications for superconductivity mechanisms in doped BaBiO3 and heterostructure design.