We investigate the electronic structure of the $2H$ and $3R$ polytypes of $\mathrm{Nb}{\mathrm{S}}_2$. The Fermi surfaces measured by angle-resolved photoemission spectroscopy show a remarkable difference in size, reflecting a significantly increased band filling in $3R-{\mathrm{Nb}}_{1+x}{\mathrm{S}}_2$ compared to $2H-\mathrm{Nb}{\mathrm{S}}_2$, which we attribute to the presence of additional interstitial Nb, which act as electron donors. Thus, we find that the stoichiometry, rather than the stacking arrangement, is the most important factor in the difference in electronic and physical properties of the two phases. Our high resolution data on the $2H$ phase shows kinks in the spectral function that are fingerprints of the electron-phonon coupling. However, the strength of the coupling is found to be much larger for the the sections of bands with Nb $4d_{x^2-y^2,xy}$ character than for the Nb $4d_{3z^2-r^2}$. Our results provide an experimental framework for interpreting the two-gap superconductivity and latent charge density wave in $2H-\mathrm{Nb}{\mathrm{S}}_2$.

• Received 16 December 2020
• Accepted 18 March 2021

DOI:https://doi.org/10.1103/PhysRevB.103.155105

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Published by the American Physical Society