Heterogeneous Ta-dichalcogenides bilayer: heavy fermions or doped Mott physics?

Recently, a series of intriguing experiments have been reported on 1H/1T bilayers of TaCh₂ (Ch=S,Se), where tunneling from the 1H surface shows metallic spectra similar to bulk 2H-TaCh₂, while the 1T surface shows a strong central peak, sometimes with satellites, as opposed to a well-defined Mott-Hubbard gap in pure 1T-TaCh₂. In these reports, the effect was interpreted as a Kondo-type hybridization between the localized spins in 1T layers and itinerant electrons in 1H layers, implying a heavy-fermion nature of the observed peak. We have calculated the electronic structure of such bilayers, and found that even at large separation there is a sizeable charge transfer (0.4-0.6 e) from 1T to 1H. We performed Dynamical Mean Field Theory (DMFT) calculations including this charge transfer, the 1T-1H hybridization and the Mott charge density wave in 1T and find that we reproduce the experiments rather well, but, contrary to previous assumptions, the role of hybridization-induced Kondo screening is negligible, although the screening enabled by the mobile holes in the 2T layer was critical. We point out that this intriguing system is closer to a doped Mott insulator than a heavy-fermion system.