  The particular shape of the Fermi surface can give rise to a number of
collective quantum phenomena in solids, such as density wave orderings or even
superconductivity. In many new iron superconductors this shape, the 'nested'
Fermi surface, is indeed observed, but its role in the formation of
spin-density waves or superconductivity is not clear. We have studied the
electronic structure of the non-magnetic LiFeAs (Tc~18K) superconductor using
angle-resolved photoemission spectroscopy. We find a notable absence of the
Fermi surface nesting, strong renormalization of the conduction bands by a
factor of three, high density of states at the Fermi level caused by a Van Hove
singularity, and no evidence for either a static or fluctuating order except
superconductivity with in-plane isotropic energy gaps. Our observations set a
new hierarchy of the electronic properties necessary for the superconductivity
in iron pnictides and, possibly, in other materials.
