Lithium Intercalation in the Anisotropic van der Waals Magnetic Semiconductor CrSBr

TL;DR

This study investigates lithium intercalation in the anisotropic magnetic semiconductor CrSBr, revealing highly directional lithium migration and its effects on electrical conductivity, with implications for doping and device fabrication.

Contribution

It provides the first real-time analysis of lithium diffusion in CrSBr, highlighting anisotropic migration and the influence of hBN coverage, supported by experimental and molecular dynamics simulations.

Findings

Lithium diffuses anisotropically with diffusion coefficients differing by over an order of magnitude.

Lithium migration follows Br-chains primarily along the a-direction.

Lithium significantly enhances electrical conductivity along the a-axis.

Abstract

Alkali metal intercalation is an important strategy for doping van der Waals materials. Lithium, in particular, was shown to achieve exceptional charge carrier densities, reaching levels at which fundamental electrical, optical, and magnetic material properties begin to be strongly modified. While lithium is known to be highly volatile, its migration dynamics in anisotropic layered crystals remain poorly understood. In this work, we investigate the intercalation of lithium in-between layers of the anisotropic magnetic semiconductor CrSBr. Using exfoliated crystals, we are able to monitor the dynamics of the intercalation process in real time through optical and electrical characterization methods. Our measurements reveal highly anisotropic migration of Lithium characterized by diffusion coefficients that differ by more than one order of magnitude along a- and b-directions. This finding is in good agreement with our molecular dynamics simulations which show trajectories of lithium atoms primarily follow the Br-chains in the a-direction. Beyond that, we find that partially covering CrSBr crystals by thin hexagonal boron nitride (hBN) flakes has a significant impact on the intercalation process, and that lithium strongly enhances the electrical conductivity along the a-axis. Our method offers a new platform for lithium diffusion studies and encourages further research to pursue the fabrication of lithium-doped devices.