Scientists have observed the thermal Hall Effect in insulators, leading to an important open question in condensed-matter physics.
Thermal Hall Effect in conductors
In the presence of a magnetic field, electrons are deflected from their paths in a perpendicular direction.
When a temperature gradient is applied in the conductor in one direction, another temperature gradient appears in a perpendicular direction in the presence of a magnetic field.
The electrons in the material carry both electric charges and thermal energy, and the magnetic field deflects them, giving rise to the perpendicular gradient.
Thermal Hall Effect in insulators
Scientists have observed the thermal Hall effect in insulators as well, especially terbium oxides and strontium titanate.
Not the electrons but the phonons in insulators are involved in transferring heat or electricity.
Phonons do not have electric charge hence can’t be deflected directly by the magnetic field.
Phonons are affected by the electrons that are deflected by the magnetic field.
They are deflected in a perpendicular direction as well.
A phonon is a quasiparticle of vibrational energy.
These packets of energy behave like particles in a system.
When the grid of atoms that make up the material vibrates, it releases this energy, and physicists encapsulate it in the form of phonons.