Pseudogap in underdoped cuprates and spin-density-wave fluctuations

We analyze fermionic spectral function in the spin-density-wave (SDW) phase of quasi-two-dimensional (quasi-2D) cuprates at small but finite T. We use a nonperturbative approach and sum up infinite series of thermal self-energy terms, keeping at each order nearly divergent (T/J) vertical bar log epsilon vertical bar terms, where epsilon is a deviation from a pure 2D, and neglecting regular T/J corrections. We show that, as SDW order decreases, the spectral function in the antinodal region acquires peak/hump structure: the coherent peak position scales with SDW order parameter while the incoherent hump remains roughly at the same scale as at T=0 when SDW order is the strongest. We identify the hump with the pseudogap observed in angle-resolved photoemission spectroscopy and argue that the presence of coherent excitations at low energies gives rise to magneto-oscillations in an applied field. We show that the same peak/hump structure appears in the density of states and in optical conductivity.