Temperature crossovers in cuprates

We study the temperature crossovers seen in the magnetic and transport properties of cuprates using a nearly antiferromagnetic Fermi liquid model (NAFLM). For the overdoped cuprates, we find, in agreement with earlier work, mean-field $z=2$ behavior of the magnetic variables associated with the fact that the damping rate of their spin fluctuations is essentially independent of temperature, while the resistivity exhibits a crossover from Fermi liquid behavior at low temperature to linear-in-T above a certain temperature $T_0$, due to the proximity of the quasiparticle Fermi surface to the magnetic Brillouin zone boundary. For the underdoped cuprates we argue that the sequence of crossovers identified by Barzykin and Pines in the low frequency magnetic behavior (from mean field $z=2$ at high temperatures, $T>T_{cr}$, to non-universal $z=1$ scaling behavior at intermediate $T$, $T_*<T<T_{cr}$, to pseudogap behavior below $T_*$) reflects the development in the electronic structure of a precursor to a spin-density-wave state. This development begins at $T_{cr}$ with a thermal evolution of the quasiparticle spectral weight which brings about temperature dependent spin-damping and ends at $T_*$ where the Fermi surface has lost pieces near corners of the magnetic Brillouin zone. For $T_*<T<T_{cr}$ the resistivity is linear in $T$ because this change in spectral weight does not affect the resistivity significantly; below $T_*$ vertex corrections act to bring about the measured downturn in $(\rho(T)-\rho(0))/T$ and approximately quadratic in $T$ resistivity for $T\ll T_*$.