  The emergence of the quantum metallic state marked by a saturating finite
electrical resistance in the zero-temperature limit in a variety of
two-dimensional superconductors injects an exciting momentum to the realm of
unconventional superconductivity. Despite much research efforts over last few
decades, there is not yet a general consensus on the nature of this unexpected
quantum metal. Here, we report the observation of a unique quantum metallic
state within the hallmark of Bose-metal characterized by a saturating
resistance and a simultaneously vanishing Hall resistance in the titanium
sesquioxide heterointerface superconductor Ti$_2$O$_3$/GaN. Remarkably, the
quantum bosonic metallic state tuned by a magnetic field in the vicinity of the
two-dimensional superconductivity-metal transition persists in the normal
phase, suggesting the existence of composite bosons, formed by electron Cooper
pairs, even in the normal phase. Our findings indicate the existence of
preformed electron Cooper pairs in the normal phase of heterointerface
superconductors, and shed new light on the pairing mechanism underlying
unconventional superconductivity.
