Origin of Unconventional Quantum Oscillations in Kagome Metals

TL;DR

This study explains the different quantum oscillation spectra in kagome metals CsTi3Bi5 and RbTi3Bi5 by modeling orbital effects and magnetic breakdown, revealing how subtle orbital differences influence topological signals.

Contribution

The paper introduces a tight-binding model linking orbital variations to quantum oscillation differences and highlights magnetic breakdown as a key factor in topological signal observation.

Findings

Distinct oscillation spectra are reproduced by the model.

Magnetic breakdown masks topological signals in RbTi3Bi5.

Orbital differences affect hybridization gaps and quantum oscillations.

Abstract

Recent quantum oscillation experiments on the kagome metals CsTi$_3$Bi$_5$ and RbTi$_3$Bi$_5$ have revealed a puzzling phenomenon: despite possessing nearly identical band structures and Fermi surface geometries, they exhibit distinct oscillation spectra and topological signals. Intuitively, the fundamental distinction between the two compounds originates from the alkali metal ions, where Cs possesses more diffuse orbitals than Rb. By using a tight-binding model, we map this orbital variation into an effective next-nearest-neighbor hopping term. Based on this framework, we successfully reproduce the distinct experimental features. Furthermore, we demonstrate that the physical origin of their distinct topological signals stems from the magnetic breakdown effect. In the RbTi$_3$Bi$_5$ case, magnetic breakdown readily occurs and masks the intrinsic topological nature. In contrast, the presence of the next-nearest-neighbor hopping in CsTi$_3$Bi$_5$ enlarges the hybridization gap, significantly reducing the magnetic breakdown probability and manifesting the nontrivial Berry phase. These findings demonstrate that magnetic breakdown plays an important role in the observation of topological properties and suggest that subtle orbital differences can lead to significant variations in quantum oscillations.