The Exploration of the Thermal Hall Effect in Insulators

The thermal hall effect (THE) is a fascinating physical phenomenon that arises when tiny transverse temperature differences occur in a material as a thermal current passes through it and a perpendicular magnetic field is applied. While this effect has been observed in various insulators, the underlying physics behind it remains poorly understood. Researchers at Université de Sherbrooke in Canada have been diligently investigating this effect in different materials to shed light on its mechanisms.

Uncovering the Mechanism

The latest paper published in Nature Physics by the researchers at Université de Sherbrooke focused on examining the THE in the antiferromagnetic insulator strontium iridium oxide (Sr2IrO4). Their research journey began with the discovery of a large THE in cuprate superconductors, a revelation that surprised many in the scientific community. Louis Taillefer, co-author of the paper, highlighted the groundbreaking nature of their findings, particularly how the large THE persisted even at zero doping in cuprates, which are Mott insulators, sparking interest among leading theorists.

Following their initial discovery, the researchers were able to identify phonons as the heat carriers responsible for the observed effect in cuprate insulators. This significant revelation laid the foundation for further investigations into the role of phonons in THE. By conducting experiments sending the heat current perpendicular to the CuO2 planes, where only phonons can travel, the researchers confirmed that phonons were indeed the relevant heat carriers.

In their recent study, Taillefer and his team delved into the impact of impurities on the phonon-induced THE in Sr2IrO4. Through the introduction of rhodium (Rh) and lanthanum (La) impurities into the material, they made a surprising discovery. The addition of a small concentration of Rh impurities led to a remarkable 70-fold increase in THE, indicating that phonon scattering off impurities embedded in an antiferromagnetic environment plays a crucial role in the observed effect.

The new findings from the study hint at a potential mechanism underlying the phonon-induced THE in Sr2IrO4, focusing on the scattering of phonons by impurities. This raises exciting possibilities for future research in exploring the role of impurities in generating THE in other materials. Additionally, the researchers plan to investigate materials that could exhibit THE from exotic emergent excitations like Majorana fermions or spinons, broadening the scope of their exploration.

Overall, the journey of uncovering the mechanisms behind the thermal hall effect in insulators is a complex and intriguing one, with each discovery leading to new questions and avenues for exploration. Through meticulous experimentation and collaboration, researchers are gradually unraveling the mysteries surrounding this fascinating phenomenon, paving the way for future advancements in the field of condensed matter physics.


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