Enhanced Thermal Hall Effect in Nearly Ferroelectric Insulators

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Physics

Background:

• Recent experiments show unexpectedly large thermal Hall conductivity (κ_{H}) in insulating La_{2}CuO_{4} (LCO) and SrTiO_{3} (STO).
• Understanding the mechanisms behind this phenomenon is crucial for materials science and thermal transport studies.

Purpose of the Study:

• To theoretically investigate the conditions under which acoustic phonons can cause a significant thermal Hall conductivity.
• To identify the dominant contributions (intrinsic vs. extrinsic) to κ_{H} in insulating materials.

Main Methods:

• Theoretical exploration of acoustic phonon contributions to thermal Hall conductivity.
• Analysis of intrinsic and extrinsic factors, including dielectric constant (ε) and flexoelectric coupling (F).

Main Results:

• Both intrinsic and extrinsic contributions to κ_{H} are proportional to the dielectric constant and flexoelectric coupling.
• The intrinsic phonon contribution is significantly smaller than experimentally observed values.
• An extrinsic contribution, dependent on the phonon mean-free path, is proposed as a likely explanation for the observed κ_{H}, especially in SrTiO_{3}.

Conclusions:

• Acoustic phonons play a role in the thermal Hall conductivity of insulating materials.
• Extrinsic effects related to phonon transport are key to explaining large observed κ_{H}.
• Further investigation into insulating perovskites may reveal materials with even larger intrinsic κ_{H}.