Disorder-induced multifractal superconductivity in monolayer niobium dichalcogenides

The interplay between disorder and superconductivity is a subtle and fascinating phenomenon in quantum many-body physics. Conventional superconductors are insensitive to dilute non-magnetic impurities, known as Anderson’s theorem1. Destruction of superconductivity and even superconductor–insulator transitions2–10 occur in the regime of strong disorder. Hence, disorder-enhanced superconductivity is rare and has been observed only in some alloys or granular states11–17. Owing to the entanglement of various effects, the mechanism of enhancement is still under debate. Here, we report a well-controlled disorder effect in the recently discovered monolayer NbSe2 superconductor. The superconducting transition temperatures of NbSe2 monolayers are substantially increased by disorder. Realistic theoretical modelling shows that the unusual enhancement possibly arises from the multifractality18,19 of electron wavefunctions. This work provides experimental evidence of the multifractal superconducting state. Disorder present in monolayer NbSe2 is found to be able to enhance its superconductivity. A systematic study reveals the origin—disorder-induced multifractality of the electron wavefunctions strengthens the local interactions.