  Interfacial interactions are crucial in a variety of fields and can greatly
affect the electric, magnetic, and chemical properties of materials. Among
them, interface orbital hybridization plays a fundamental role in the
properties of surface electrons such as dispersion, interaction, and ground
states. Conventional measurements of electronic states at interfaces such as
scanning tunneling microscopes are all based on electric interactions which,
however, suffer from strong perturbation on these electrons. Here we unveil a
new experimental detection of interface electrons based on the weak magnetic
interactions between them and the nitrogen-vacancy (NV) center in diamond. With
negligible perturbation on the interface electrons, their physical properties
can be revealed by the NV spin coherence time. In our system, the interface
interaction leads to significant decreases in both the density and coherence
time of the electron spins at the diamond-graphene interface. Furthermore,
together with electron spin resonance spectra and first-principle calculations,
we can retrieve the effect of interface electron orbital hybridization. Our
study opens a new pathway toward the microscopic probing of interfacial
electronic states with weak magnetic interactions and provides a new avenue for
future research on material interfaces.
