Slow spin dynamics in a 2D dipolar spin ensemble on the surface of diamond

We observe remarkably slow local spin dynamics in a two-dimensional disordered many-body dipolar spin system, formed by naturally-occurring electronic spins on the surface of a diamond crystal. Shallow NV centers are used to access individual spins, or small spin sub-ensembles. We characterize and control the strength of disorder and dipolar interactions among the surface electronic spins, and measure spin transport at the level of single-spin correlation functions. We model the observed spin relaxation dynamics with a combination of exact dynamics simulation for nearest-neighbor spins, and a dynamical mean-field treatment of the rest of the spin ensemble.