1 research outputs found
Electronic structure of 2H-NbSe<sub>2</sub> single-layers in the CDW state
A density functional theory study of NbSe single-layers in the normal
non-modulated and the CDW states is reported. We show that, in the
single layer, the CDW barely affects the Fermi surface of the system, thus
ruling out a nesting mechanism as the driving force for the modulation. The CDW
stabilizes levels lying around 1.5 eV below the Fermi level within the Se-based
valence band but having a substantial Nb-Nb bonding character. The absence of
interlayer interactions leads to the suppression of the pancake-like portion of
the bulk Fermi surface in the single-layer. We perform scanning tunneling
microscopy simulations and find that the images noticeably change with the sign
and magnitude of the voltage bias. The atomic corrugation of the Se sublayer
induced by the modulation plays a primary role in leading to these images, but
the electronic reorganization also has an important contribution. The analysis
of the variation of these images with the bias voltage does not support a Fermi
surface nesting mechanism for the CDW. It is also shown that underlying
graphene layers (present in some of the recent experimental work) do not modify
the conduction band, but do affect the shape of the valence band of NbSe
single-layers. The relevance of these results in understanding recent physical
measurements for NbSe single-layers is discussed