Weak Pseudogap Behavior in the Underdoped Cuprate Superconductors

We report on a novel solution of the nearly antiferromagnetic (AF) spin fermion model in the limit $\pi T\gg {\omega }_{\mathrm{sf}}$, which demonstrates that the broad high energy features found in angular resolved photoemission spectroscopy measurements of the spectral density of the underdoped cuprates are determined by strong (AF) correlations and precursor effects of a spin density wave state. We show that the onset temperature, $T^{\mathrm{cr}}$, of weak pseudogap behavior is determined by the strength, $\xi$, of the (AF) correlations, and obtain the generic changes in low frequency magnetic behavior seen in NMR experiments with $\xi \left(T^{\mathrm{cr}}\right)\approx 2$, confirming the Barzykin and Pines crossover criterion.