  Although initially introduced to mimic the spin-ice pyrochlores, no
artificial spin ice has yet exhibited the expected degenerate ice-phase with
critical correlations similar to the celebrated Coulomb phase in the pyrochlore
lattice. Here we study a novel artificial spin ice based on a vertex-frustrated
rather than pairwise frustrated geometry and show that it exhibits a
quasicritical ice phase of extensive residual entropy and, significantly,
algebraic correlations. Interesting in its own regard as a novel realization of
frustration in a vertex system, our lattice opens new pathways to study defects
in a critical manifold and to design degeneracy in artificial magnetic
nanoarrays, a task so far elusive.
