Layer sliding and twisting induced electronic transitions in correlated magnetic 1T-NbSe${}_2$ bilayers

Correlated 2D layers, like 1T-phases of TaS${}_2$, TaSe${}_2$, and NbSe${}_2$, exhibit rich tunability through varying interlayer couplings, which promotes the understanding of electron correlation in the 2D limit. However, the coupling mechanism is, so far, poorly understood and is tentatively ascribed to interactions among the d${}_{z^2}$ orbitals of Ta or Nb atoms. Here, it is theoretically shown that the interlayer hybridization and localization strength of interfacial Se p${}_z$ orbitals, rather than Nb d${}_{z^2}$ orbitals, govern the variation of electron-correlated properties upon interlayer sliding or twisting in correlated magnetic 1T-NbSe${}_2$ bilayers. Each of the layers is in a star-of-David (SOD) charge-density-wave phase. Geometric and electronic structures and magnetic properties of 28 different stacking configurations are examined and analyzed using density-functional-theory calculations. It is found that the SOD contains a localized region, in which interlayer Se p${}_z$ hybridization plays a paramount role in varying the energy levels of the two Hubbard bands. These variations lead to three electronic transitions among four insulating states, which demonstrate the effectiveness of interlayer interactions to modulate correlated magnetic properties in a prototypical correlated magnetic insulator. (© 2023 Wiley‐VCH GmbH)