Anisotropy in the electronic structure ofV2GeCinvestigated by soft x-ray emission spectroscopy and first-principles theory

The anisotropy of the electronic structure of ternary nanolaminate ${\text{V}}_2\text{GeC}$ is investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependent emission spectra of $\text{V}{L}_{2,3}$, $\text{C}K$, $\text{Ge}{M}_1$, and $\text{Ge}{M}_{2,3}$ in ${\text{V}}_2\text{GeC}$ are compared with those from monocarbide VC and pure Ge. The experimental emission spectra are interpreted with calculated spectra using ab initio density-functional theory including dipole transition matrix elements. Different types of covalent chemical bond regions are revealed: $\text{V}3d\text{-C}2p$ bonding at $-3.8\text{eV}$, $\text{Ge}4p\text{-C}2p$ bonding at $-6\text{eV}$, and $\text{Ge}4p\text{-C}2s$ interaction mediated via the $\text{V}3d$ orbitals at $-11\text{eV}$ below the Fermi level. We find that the anisotropic effects are high for the $4p$ valence states and the shallow $3d$ core levels of Ge, while relatively small anisotropy is detected for the $\text{V}3d$ states. The macroscopic properties of the ${\text{V}}_2\text{GeC}$ nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work.