Charge-density-wave gap in the quasi-two-dimensional conductor Na0.9Mo6O17 measured by angle-resolved photoemission spectroscopy -: art. no. 035115

The charge-density-wave gap in the quasi-two-dimensional conductor Na0.9Mo6O17 has been measured using angle-resolved photoemission spectroscopy. The gap opening is accompanied by the creation of a new zone boundary and a subsequent backfold of the bands. The position of the point of minimum binding energy of the band dispersion has been determined in both energy and momentum. A change of the momentum of this point at very low temperatures is consistent with the existence of a second phase transition, previously observed by magnetic susceptibility and specific heat measurements. Symmetry arguments are used to show that the features found in the electronic structure are best described by using the monoclinic nomenclature, even though the measured low-energy electron diffraction patterns are hexagonal.