Abstract
Using angle-resolved photoemission spectroscopy, we report on the
direct observation of the energy gap in 2H-NbSe2 caused by the charge-density
waves (CDW). The gap opens in the regions of the momentum space connected
by the CDW vectors, which implies a nesting mechanism of CDW formation.
In remarkable analogy with the pseudogap in cuprates, the detected
energy gap also exists in the normal state (T>T0) where it breaks
the Fermi surface into “arcs,” it is nonmonotonic as a function of
temperature with a local minimum at the CDW transition temperature
(T0), and it forestalls the superconducting gap by excluding the
nested portions of the Fermi surface from participating in superconductivity.
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