Electronic structure of η-Mo4O11 studied by high-resolution angle-resolved photoemission spectroscopy

We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on a quasi-two-dimensional (2D) conductor eta-Mo4O11 1, which undergoes a two-stage charge density wave (CDW) transition at 109 and 35 K. We have succeeded in experimentally mapping out the two-dimensional Fermi surface (FS) as well as directly observing two different CDW gaps. We found that the two-dimensional FS of eta-Mo4O11 consists of two "hidden one-dimensional (ID) FSs" originating in two almost independent conducting paths in the crystal. We also found that the gap energy and the temperature dependence are different for the two CDW gaps. The present ARPES results indicate that the characteristic CDW transition in eta-Mo4O11 is driven by the instability of two "hidden ID FSs". (c) 2005 Elsevier B.V. All rights reserved.