Antiferromagnetic FeSn is considered to be a close realization of the ideal two-dimensional (2D) kagome lattice, hosting Dirac cones, van Hove singularities, and flat bands, as it comprises ${\mathrm{Fe}}_3\mathrm{Sn}$ kagome layers well separated by Sn buffer layers. We observe a pronounced optical anisotropy, with the low-energy optical conductivity being surprisingly higher perpendicular to the kagome planes than along the layers. This finding contradicts the prevalent picture of dominantly 2D electronic structure for FeSn. Our material-specific theory reproduces the measured conductivity spectra remarkably well. A site-specific decomposition of the optical response to individual excitation channels shows that the optical conductivity for polarizations both parallel and perpendicular to the kagome plane is dominated by interlayer transitions between kagome layers and adjacent Sn-based layers. Moreover, the matrix elements corresponding to these transitions are highly anisotropic, leading to larger out-of-plane conductivity. Our results evidence the crucial role of interstitial layers in charge dynamics even in seemingly 2D systems.

Close

PrevNext

View figure in article

• Electronic structure
• Optical conductivity
• Topological phases of matter
• Weyl semimetal
• Density functional theory
• Fourier transform infrared spectroscopy