Magnetic-field-tuned superconductor-to-insulator transition via mosaic phase in cuprate thin films

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The magnetic-field-induced superconductor-to-insulator transition (SIT) was investigated in highly disordered La 1.85 Sr 0.15 CuO 4 thin films. By systematically reducing the film thickness, disorder effects were enhanced, leading to the coexistence of superconducting and insulating phases at low temperatures. Electronic transport measurements revealed the formation of an intermediate mosaic phase, where localized Cooper pairs coexist with a coherent superconducting state. Near the quantum phase transition, scaling analysis determined a critical resistance R c = 5.72 kΩ, consistent with the universal quantum resistance R Q = h /4 e 2 for Cooper pairs. The critical product of the spatial and dynamic critical exponents aligns with the classical percolation universality class, emphasizing the role of percolation in governing the SIT under strong disorder. These results provide new insights into the quantum critical behavior and phase evolution of disordered superconducting systems. • Film thickness affects the superconductivity of high- T c cuprate thin films. • Disorder effect enhanced by decreasing film thickness drives a superconductor-to-insulator transition. • Features of a bosonic superconductor-to-insulator transition are observed, such as the appearance of the universal quantum resistance R Q for 2 e -charge bosons. • Scaling analysis reveals the magnetic-field-induced quantum phase transition of disordered La 1.85 Sr 0.15 CuO 4 thin films belongs to the universality class of classical percolation, which supports a coexistence of superconducting and insulating phases.