Temperature-dependent electronic structure of a quasi-two-dimensional conductor η-Mo₄O₁₁

The origin of the temperature-dependent physical properties of η-Mo₄O₁₁ has been a topic discussed for a couple of decades. By using a photoelectron momentum microscope, we measured the Fermi surfaces and band structures of this material at 150 K, 70 K, and 20 K, i.e., above, between, and below the temperatures where two charge density wave (CDW) transitions were reported to occur in the literature. Three metallic Fermi surfaces with 1D character along the b^* and b^* ± c^* axes were clearly observed at these three temperatures with a negligible difference, suggesting that η-Mo₄O₁₁ does not show CDW transition in the measured temperature range. No trace of CDW transition was observed in the spectra of the three metallic bands near the Fermi level as well. Based on these results and theoretical supports, we discuss the origin of the two conflicting results on the temperature-dependent physical property of η-Mo₄O₁₁.