Inverse Proximity Effect and Unconventional Superconductivity in the Pb/CrTe Hybrid Thin Films

Many intriguing phenomena, including triplet pairing and the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, can emerge in superconductor/ferromagnet hybrid thin films. Here, we systematically investigate two-dimensional Pb/CrTe superconductor/ferromagnet hybrids using scanning tunneling microscopy and transport measurements. We reveal a pronounced inverse proximity effect, manifested by an unconventional superconducting gap structure, a reduction of the superconducting transition temperature by more than 50%, and a suppression of the upper critical field by over an order of magnitude. In addition, the oscillation of the superconducting transition temperature of hybrid films with the ferromagnetic layer thickness is observed, providing evidence of FFLO-like states. Furthermore, the oscillatory behavior evolves into a re-entrant superconducting state under an applied magnetic field. Our experiments shed new light on interfacial interactions and unconventional superconductivity in atomically thin superconductor/ferromagnet hybrid films.