Hidden Charge-Density-Wave Order in a Low-Tc Superconductor 2H-NbSe2

The Charge-density-wave(CDW) in 2H-NbSe2(TCDW ~ 33 K), which coexists with superconductivity(Tc = 7.2 K), is investigated using Angle-resolved photoemission spectroscopy as a function of temperature. Across TCDW, energy and momentum(k) distribution curves show changes associated with the primary and secondary CDW vectors. The CDW is due to hidden charge order occurring at specific k-points on Fermi surfaces in the 2-dimensional Brillouin zone(2D BZ) with spectral weight suppression, but no gap formation. The study rules out nesting in the 2D BZ and the van Hove singularity driven CDW transition in 2H-NbSe2.