What is the minimal condition for a phonon to couple to a magnetic field and bend its trajectory?

• Grant number: 24/16100-9
• Support Opportunities: Regular Research Grants
• Start date: December 01, 2024
• End date: November 30, 2029
• Field of knowledge: Physical Sciences and Mathematics - Physics - Condensed Matter Physics
• Principal Investigator: Valentina Martelli
• Grantee: Valentina Martelli
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The thermal Hall effect (THE) is the thermal analogue of the Hall effect, where a charge flow changes the trajectory because of the Lorentz force by applying a perpendicular magnetic field. Compared to the Electronic Hall effect, which has been investigated in depth and is frequently employed to detect exotic electronic states, THE is still not understood from a fundamental standpoint despite having been observed in a growing number of materials. When the THE is observed in an insulator, phonons (or possibly any other neutral heat carriers), which are charge-less and spin-less excitations, are said to acquire handedness. Both intrinsic (thermal carriers coupled to field-sensitive mechanism) and extrinsic mechanisms (impurities and defects) have been put forward to explain this phenomenon. Exotic chargeless excitations (ex. Majorana fermions), which are expected to open a gap in their bands under the effect of a magnetic field, were predicted to show a peculiar signature on THE. In this project, we will perform a systematic investigation of THE down to low temperatures (1.5-300K) and under a magnetic field up to 9T on a series of naturally occurring crystals with a controlled degree of impurities, of sample crystallinity, and structural chirality. The experiments will be carried out on home-made platforms and are expected to provide new relevant insights and advance the understanding of the minimal conditions needed for a phonon to bend in the presence of a magnetic field. (AU)