Proximity effects in the charge density wave order and superconductivity in single-layer NbSe₂

Collective electronic states such as the charge density wave (CDW) order and superconductivity respond dramatically to external perturbations. In two-dimensional materials hosting such states, the closeness to unavoidable supporting substrates may lead to significant changes in their properties. Here we explore the impact of proximity effects on the CDW and superconducting states in single-layer NbSe₂. We performed the electronic characterization of single-layer NbSe₂ on several substrates of opposite metallicity by means of STM/STS at 350 mK, ARPES and 4-point probe transport measurements. In particular, we have epitaxially grown single-layer NbSe₂ by MBE on two different metals, Au(111) and BLG/SiC(0001), and two insulators, bulk WSe₂ and monolayer h-BN/Ir(111). While both phases disappear on Au(111), they persist on BLG/SiC. The fate of the CDW and superconducting phases is more intricate on insulating substrates, which are largely affected, however, despite of the electronic decoupling of the 2D superconductor with the substrate states.