Abstract
Anomalous metallic behavior, marked by a saturating finite resistivity much lower than the Drude estimate, has been observed in a wide range of two-dimensional superconductors. Utilizing the electrostatically gated LaAlO3/SrTiO3 interface as a versatile platform for superconductor-metal quantum phase transitions, we probe variations in the gate, magnetic field, and temperature to construct a phase diagram crossing from superconductor, anomalous metal, vortex liquid, to the Drude metal state, combining longitudinal and Hall resistivity measurements. We find that the anomalous metal phases induced by gating and magnetic field, although differing in symmetry, are connected in the phase diagram and exhibit similar magnetic field response approaching zero temperature. Namely, within a finite regime of the anomalous metal state, the longitudinal resistivity linearly depends on the field while the Hall resistivity diminishes, indicating an emergent particle-hole symmetry. The universal behavior highlights the uniqueness of the quantum bosonic metallic state, distinct from bosonic insulators and vortex liquids.
Highlights
The anomalous metallic state observed in various two-dimensional (2D) superconductors[1], including the LaAlO3/SrTiO3 interface[2,3,4,5], has attracted attentions recently
Nine unit cells of LaAlO3 is epitaxially grown on top of a 0.5 mm thick SrTiO3 substrate after patterning AlOx hard mask, defining a 0.4 mm wide conducting channel
The polar nature of the wide-bandgap LaAlO3 leads to a conductive interface with mobile electrons occupying the conduction band of SrTiO3, confined against the interface[25] (Fig. 1b)
Summary
The anomalous metallic state observed in various two-dimensional (2D) superconductors[1], including the LaAlO3/SrTiO3 interface[2,3,4,5], has attracted attentions recently. The implication for thin film superconductors is that the only admissible ground states are superconductors and insulators: metallic phases and their associated transitions are prohibited, and any experimental observations to the contrary have been deemed anomalous. This viewpoint has persisted for over four decades, despite the extended history of observing metallic behaviors approaching zero temperature in 2D systems[8,9,10,11,12,13]. These studies, conducted in different ranges of temperatures
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