  Ultrathin CrSBr flakes are exfoliated \emph{in situ} on Au(111) and Ag(111)
and their electronic structure is studied by angle-resolved photoemission
spectroscopy. The thin flakes' electronic properties are drastically different
from those of the bulk material and also substrate-dependent. For both
substrates, a strong charge transfer to the flakes is observed, partly
populating the conduction band and giving rise to a highly anisotropic Fermi
contour with an Ohmic contact to the substrate. The fundamental CrSBr band gap
is strongly renormalized compared to the bulk. The charge transfer to the CrSBr
flake is substantially larger for Ag(111) than for Au(111), but a rigid energy
shift of the chemical potential is insufficient to describe the observed band
structure modifications. In particular, the Fermi contour shows a Lifshitz
transition, the fundamental band gap undergoes a transition from direct on
Au(111) to indirect on Ag(111) and a doping-induced symmetry breaking between
the intra-layer Cr magnetic moments further modifies the band structure.
Electronic structure calculations can account for non-rigid Lifshitz-type band
structure changes in thin CrSBr as a function of doping and strain. In contrast
to undoped bulk band structure calculations that require self-consistent $GW$
theory, the doped thin film properties are well-approximated by density
functional theory if local Coulomb interactions are taken into account on the
mean-field level and the charge transfer is considered.

Strongly Correlated Electrons;Materials Science