WEAK PSEUDOGAP BEHAVIOR IN THE UNDERDOPED CUPRATE SUPERCONDUCTORS

We report on a novel solution of the nearly antiferromagnetic (AF) spi n fermion model in the limit pi T much greater than omega(sf), which d emonstrates that the broad high energy features found in angular resol ved photoemission spectroscopy measurements of the spectral density of the underdoped cuprates are determined by strong (AF) correlations an d precursor effects of a spin density wave state. We show that the ons et temperature, T-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(T- cr) approximate to 2, confirming the Barzykin and Pines crossover crit erion.