The Magneli phase Ti4O7 exhibits two sharp jumps in resistivity with coupled structural transitions as a function of temperature at Tc1=142 K and Tc2=154 K. We have studied electronic structure changes across the two transitions using 7 eV laser, soft x-ray and hard x-ray (HX) photoemission spectroscopy (PES). Ti 2p-3d resonant PES and HX-PES show a clear metallic Fermi-edge and mixed valency above Tc2. The low temperature phase below Tc1 shows a clear insulating gap of 100 meV. The intermediate phase between Tc1 and Tc2 indicates a pseudogap coexisting with remnant coherent states. HX-PES and complementary calculations have confirmed the coherent screening in the strongly correlated intermediate phase. The results suggest existence of a highly anomalous state sandwiched between the mixed-valent Fermi liquid and charge ordered Mott-insulating phase in Ti4O7.
@article{arxiv.0902.3701,
title = {Anomalous State Sandwiched between Fermi Liquid and Charge Ordered Mott-Insulating Phases of Ti4O7},
author = {M. Taguchi and A. Chainani and M. Matsunami and R. Eguchi and Y. Takata and M. Yabashi and K. Tamasaku and Y. Nishino and T. Ishikawa and S. Tsuda and S. Watanabe and C. -T. Chen and Y. Senba and H. Ohashi and K. Fujiwara and Y. Nakamura and H. Takagi and S. Shin},
journal= {arXiv preprint arXiv:0902.3701},
year = {2010}
}