Unique Quantum Metallic\nState in Ti<sub>2</sub>O<sub>3</sub>/GaN

The emergence of quantum metallic state marked by a saturating\nfinite electrical resistance in the zero-temperature limit in a variety\nof 2D superconductors injects an exciting momentum into the realm\nof heterostructure superconductivity. Despite much research effort\nover the last few decades, there is not yet a general consensus on\nthe nature of this unexpected quantum metal. Here, we report the observation\nof a unique quantum metallic state within the hallmark of Bose-metal\nin Ti<sub>2</sub>O<sub>3</sub>/GaN. Remarkably, the quantum bosonic\nmetallic state continuously tuned by a magnetic field in the vicinity\nof the two-dimensional superconductivity-metal transition persists\nin the normal phase, indicating the existence of composite bosons\nformed by electron Cooper pairs even in the normal phase. Our findings\nprovide distinct evidence for electron pairing in the normal phase\nof heterointerface superconductors and shed fresh light on the pairing\nnature underlying heterointerface superconductivity.