  The existence of rich Fermiology in anomalous metal phase in exotic
superconductors has attracted considerable interests, as exemplified in copper,
iron-based, and intermetallic frustrated kagome-based compounds. A common
feature in these cases is pseudo-gap opening or long-range lattice/electronic
ordering above superconducting critical temperature Tc. As yet developed area
is the potential existence of exotic Fermiology in superconducting transition
metal oxides on a geometrically frustrated lattice. Here, we focus on the
spinel oxide superconductor LiTi2O4, which can be viewed as the hole-doped side
of the orbital ordered 3d1 Mott system on the Ti-derived pyrochlore frustrated
network. By the in-situ combination of angle-resolved photoemission
spectroscopy (ARPES) and epitaxial thin film growth, we discovered the abrupt
flattening of near Fermi energy dispersion below the characteristic temperature
T* ~ 150 K. While the emergent negative thermal expansion below T* strongly
supports a distinct phase at low-temperature, absence of energy gap opening,
splitting/folding of bands, nor long-range lattice distortion are seen across
T*. We propose that the competition between growing instability towards orbital
ordering and its inherent geometric frustration in the Ti-pyrochlore network
results in a new quantum state of matter with robust high entropic nature below
T*. Our findings collectively point to a unique Fermiology in frustrated
three-dimensional transition metal oxides, and its connection to
superconductivity below Tc is open as an interesting future challenge. Also, a
potential guideline is unexpectedly provided for designing zero thermal
expansion metal to develop future solid-state devices.
