Manipulating Quantum Criticality in Light-induced 2D superconductivity

The creation and control of two-dimensional (2D) superconductivity in clean systems are pivotal for exploring quantum phase transitions and emergent quantum phenomena. Here, we demonstrate the realization of robust 2D superconductivity on the surface of the bulk organic Mott insulator κ-(BEDT-TTF)₂Cu[N(CN)₂]Cl (κ-Cl) [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene] by employing a monolayer of a photochromic spiropyran derivative. This approach enables light-driven carrier injection without the need for conventional field-effect device configurations, preserving the material's intrinsic structural integrity. Homogeneous photo-induced doping leads to near clean-limit 2D superconductivity, as evidenced by the observation of the Berezinskii-Kosterlitz-Thouless transition and pronounced anisotropy in the upper critical magnetic fields, indicative of a superconducting phase confined to a few molecular layers. Furthermore, by introducing controlled spatial inhomogeneity in the doping profile through partial photoisomerization, we realize a tunable degree of electronic disorder. This controlled disorder allows access to exotic quantum critical phenomena such as quantum Griffiths singularity (QGS) during the magnetic-field-driven superconductor-insulator transition. Our findings establish a versatile, non-invasive platform for inducing and manipulating 2D superconductivity on bulk crystals, providing new opportunities for studying low-dimensional superconductivity and disorder-enabled quantum phase transitions with high tunability.