Description
We report transport measurements of a two-dimensional semiconductor-superconductor hybrid Josephson-junction array with a double-layer electrostatic gate, enabling independent in situ voltage-tuned inter-island coupling and proximity-induced superconductivity. We use this voltage to drive and study superconductor-insulator (SIT) and superconductor-metal (SMT) transitions within the same device. For each transition, we identify the critical resistivity from isotherm crossings and extract critical exponents via finite-temperature scaling. We find that the critical resistivity approaches h/4e^2 near the triple point, where the superconducting, metallic and insulating states meet in the gate-voltage space. Away from this point, enhancing the proximity-induced coupling increases the SIT critical resistivity while the scaling exponent remains roughly constant. In contrast, increasing the inter-island coupling systematically decreases both the SMT critical resistivity and the associated exponent. This decrease roughly coincides with a voltage-tuned crossover of the metallic state from weak localization to weak antilocalization. Based on this we discuss whether the critical behavior is sensitive to the magnitude and sign of quantum-interference corrections in the metallic regime.
| Field of study | Quantum Physics |
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| Supervisor | Saulius Vaitiekenas |