Hidden One Dimensionality and Non-Fermi Liquid ARPES Lineshapes of the Electronic Structure of η-Mo4O11

η-Mo4O11 is a layered metal that undergoes two charge density wave (CDW) transitions at 109 K and 30 K, and is unique in showing a bulk quantum Hall effect [1]. Research so far indicates that this material has a “hidden one-dimensional” (hidden-1d) Fermi surface (FS) in the normal state (T > 109 K), whose nesting property drives the 109 K CDW formation [2]. Here, we directly confirm this picture by angle resolved photoemission spectroscopy (ARPES). Figure 1 shows the Fermi energy intensity map measured at T=150K and with hν=17eV at the 4m-NIM line of the Synchrotron Radiation Center. The geometry of the FS is in good general agreement with that of the band calculation, and can be seen as two vertical lines of hidden-1d FS coming from chains along the crystal b axis and double oblique hidden 1-d lines coming from chains along the crystal (b±c) axes. The latter are characterized by a single nesting vector QCDW, similar to the situation of other 2-d hidden-1d materials like NaMo6O17 and KMo6O17 [3]. Fig 2 shows the temperature dependent change of the valence band spectrum at point A and B respectively. We have observed that there is a small gap opening of size ~15meV only at the point A accompanied with a change in the line shape, while at the point B, which is a part of the remnant FS that is not nested by QCDW, the spectrum does not show any change as the temperature decreases. Even more interesting, this material also shows the same ARPES line shape anomalies and lack of Fermi edge in the angle integrated spectrum, that we have identified in other low dimensional metals and that are most easily rationalized within an electron fractionalization scenario that includes for the quasi-2d systems the idea of a “melted holon” part of the lineshape, arising from disorder [4]. This lineshape is neatly confined to the electronic bandwidth but is essentially featureless in energy and k. It is best seen in a region of k-space where all dispersing peaks lie above the Fermi energy. Fig. 3 shows the “melted holon” lineshape of η-Mo4O11 obtained at such a point in k-space, along the yellow line marked in the Fig. 1. Disorder that could be responsible is known in this material [5]. More detailed studies on the lineshapes and also of the 30 K CDW transition are in progress.