DIRECT FERMI-SURFACE IMAGE OF HIDDEN NESTING FOR NAMO6O17 AND KMO6O17

We report direct Fermi-surface images obtained with angle-resolved pho toemission spectroscopy (ARPES) for NaMo6O17 and KMo6O17 above the cha rge-density wave transition temperatures. We also report ARPES spectra of the valence band of NaMo6O17. The images imply a Fermi surface (FS ) based on three underlying quasi-one-dimensional (quasi-1D) surfaces. Thus it agrees in detail with that expected in the hidden nesting pic ture of Whangbo et al. [Science 252, 96 (1991)], but differs greatly f rom a FS deduced in a previous study by Breuer et al. [Phys. Rev. Lett . 76, 3172 (1996)], which found only two underlying quasi-1D surfaces.