Destruction of Fermi-liquid quasiparticles in two dimensions by critical fluctuations

It is shown that an analytic approach which includes vertex corrections in a paramagnon-like self-energy can quantitatively explain the two-dimensional Hubbard model in the weak-to-intermediate coupling regime. All parameters are determined self-consistently. This approach clearly shows that in two dimensions Fermi-liquid quasiparticles disappear in the finite-temperature paramagnetic state when the antiferromagnetic correlation length becomes larger than the electronic thermal de Broglie wavelength. Quantum Monte Carlo results are used to compare the accuracy of this approach with others.