Chiral Phonons in 2D Halide Perovskites

TL;DR

This paper demonstrates the existence of chiral phonons in 2D halide perovskites and their potential role in spin and heat transport phenomena, using machine learning to confirm their properties.

Contribution

The study confirms chiral phonons in 2D halide perovskites using machine learning force fields, highlighting their role in spin and heat current effects.

Findings

Chiral phonons are confirmed in 2D halide perovskites.

Low-energy phonons from the inorganic framework exhibit chirality.

Chiral phonons generate angular momentum under temperature gradients.

Abstract

Phonons in chiral crystal structures can be circularly polarized, making them chiral. Chiral phonons carry angular momentum, which is observable in heat currents, and, via coupling to electron spin, in spin currents. Two-dimensional (2D) halide perovskites, versatile direct band gap semiconductors, can easily form chiral structures by incorporating chiral organic cations. As a result, they exhibit phenomena such as chirality-induced spin selectivity (CISS) and the spin Seebeck effect, although the underlying mechanisms remain unclear. Using on-the-fly machine-learning force fields trained against density functional theory calculations, we confirm the presence of chiral phonons, a potential key factor for these effects. Our analysis reveals that low-energy phonons, originating from the inorganic framework, primarily exhibit chirality. Under a temperature gradient, these chiral phonons generate substantial angular momentum, leading to experimentally observable effects. These findings position chiral 2D perovskites as a promising platform for exploring the interplay between phononic, electronic, spintronic, and thermal properties.