This article reports the experimental observation and theoretical modeling of quantum spin liquid (QSL) signatures in monolayer 1T-NbSe₂, a two-dimensional material that exhibits both charge-density-wave (CDW) and correlated insulating behaviors. Using scanning tunneling microscopy and spectroscopy (STM/STS), the researchers confirmed the presence of spin fluctuations in monolayer 1T-NbSe₂ by observing Kondo resonance when it interacts with metallic monolayer 1H-NbSe₂. Further STM/STS imaging revealed long-wavelength charge modulation, consistent with spinon modulation expected for QSLs. Depositing manganese-phthalocyanine (MnPc) molecules with spin S=3/2 onto monolayer 1T-NbSe₂ resulted in new STS resonance peaks at the Hubbard band edges, consistent with the spinon Kondo effect induced by a S=3/2 magnetic impurity in a QSL. These findings suggest that monolayer 1T-NbSe₂ is a promising QSL material. Quantum spin liquids are a quantum disordered state with fractionalized excitations and no magnetic order even at zero temperature. They are predicted to host spinon excitations and arise in frustrated spin systems with large quantum fluctuations. Monolayer 1T-NbSe₂, a newly emerging two-dimensional material, is a correlated insulator with a triangular lattice. Upon cooling, it undergoes a commensurate CDW phase transition, resulting in a well-ordered triangular CDW lattice. The material exhibits a correlated insulating state with a flat band split into upper and lower Hubbard bands (UHB and LHB) due to Coulomb repulsion. The material's crystalline and electronic structure is similar to QSL candidates 1T-TaS₂ and 1T-TaSe₂, making it important to investigate its nature. The study used STM/STS measurements and theoretical modeling to confirm QSL behavior in monolayer 1T-NbSe₂. The researchers investigated the modified density of states (DOS) in single 1T-NbSe₂ layers on an electronically passive substrate in the presence and absence of a metallic spacer layer of 1H-NbSe₂. In the presence of the metal layer, periodic Kondo resonance peaks were observed, indicating localized spins in each SOD motif. In the absence of the metal layer, STS images revealed long-wavelength modulation, evidence of standing waves from fractionalized quasiparticles in the correlated insulating gap. Depositing a magnetic molecule with S=3/2 spin onto monolayer 1T-NbSe₂ resulted in new resonance peaks at the Hubbard band edges, consistent with the spinon Kondo effect. The study also demonstrated that monolayer 1T-NbSe₂ hosts local spin excitations, contains correlated in-gap carriers, and readily forms a Kondo screening cloud around aThis article reports the experimental observation and theoretical modeling of quantum spin liquid (QSL) signatures in monolayer 1T-NbSe₂, a two-dimensional material that exhibits both charge-density-wave (CDW) and correlated insulating behaviors. Using scanning tunneling microscopy and spectroscopy (STM/STS), the researchers confirmed the presence of spin fluctuations in monolayer 1T-NbSe₂ by observing Kondo resonance when it interacts with metallic monolayer 1H-NbSe₂. Further STM/STS imaging revealed long-wavelength charge modulation, consistent with spinon modulation expected for QSLs. Depositing manganese-phthalocyanine (MnPc) molecules with spin S=3/2 onto monolayer 1T-NbSe₂ resulted in new STS resonance peaks at the Hubbard band edges, consistent with the spinon Kondo effect induced by a S=3/2 magnetic impurity in a QSL. These findings suggest that monolayer 1T-NbSe₂ is a promising QSL material. Quantum spin liquids are a quantum disordered state with fractionalized excitations and no magnetic order even at zero temperature. They are predicted to host spinon excitations and arise in frustrated spin systems with large quantum fluctuations. Monolayer 1T-NbSe₂, a newly emerging two-dimensional material, is a correlated insulator with a triangular lattice. Upon cooling, it undergoes a commensurate CDW phase transition, resulting in a well-ordered triangular CDW lattice. The material exhibits a correlated insulating state with a flat band split into upper and lower Hubbard bands (UHB and LHB) due to Coulomb repulsion. The material's crystalline and electronic structure is similar to QSL candidates 1T-TaS₂ and 1T-TaSe₂, making it important to investigate its nature. The study used STM/STS measurements and theoretical modeling to confirm QSL behavior in monolayer 1T-NbSe₂. The researchers investigated the modified density of states (DOS) in single 1T-NbSe₂ layers on an electronically passive substrate in the presence and absence of a metallic spacer layer of 1H-NbSe₂. In the presence of the metal layer, periodic Kondo resonance peaks were observed, indicating localized spins in each SOD motif. In the absence of the metal layer, STS images revealed long-wavelength modulation, evidence of standing waves from fractionalized quasiparticles in the correlated insulating gap. Depositing a magnetic molecule with S=3/2 spin onto monolayer 1T-NbSe₂ resulted in new resonance peaks at the Hubbard band edges, consistent with the spinon Kondo effect. The study also demonstrated that monolayer 1T-NbSe₂ hosts local spin excitations, contains correlated in-gap carriers, and readily forms a Kondo screening cloud around a