  We investigate the doped two-dimensional Hubbard model at finite temperature
using controlled diagrammatic Monte Carlo calculations allowing for the
computation of spectral properties in the infinite-size limit and, crucially,
with arbitrary momentum resolution. We show that three distinct regimes are
found as a function of doping and interaction strength, corresponding to a
weakly correlated metal with properties close to those of the non-interacting
system, a correlated metal with strong interaction effects including a
reshaping of the Fermi surface, and a pseudogap regime at low doping in which
quasiparticle excitations are selectively destroyed near the antinodal regions
of momentum space. We study the physical mechanism leading to the pseudogap and
show that it forms both at weak coupling when the magnetic correlation length
is large and at strong coupling when it is shorter. In both cases, we show that
spin-fluctuation theory can be modified in order to account for the behavior of
the non-local component of the self-energy. We discuss the fate of the
pseudogap as temperature goes to zero and show that, remarkably, this regime
extrapolates precisely to the ordered stripe phase found by ground-state
methods. This handshake between finite temperature and ground-state results
significantly advances the elaboration of a comprehensive picture of the
physics of the doped Hubbard model.
