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

The magnetic-field-induced superconductor-to-insulator transition (SIT) was investigated in highly disordered La_1.85Sr_0.15CuO₄ 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/4e² for Cooper pairs. The critical product of the spatial and dynamic critical exponents $z\nu =1.33$ 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.