Crossover from the 2D Heisenberg to the 1D Quantum Spin Ladder Regime in Underdoped High Tc Cuprates

The enigmatic scaling behaviour of the normal state properties of the high Tc cuprates has been explained by assuming that a crossover from the two- dimensional Heisenberg (2D-H) to the one-dimensional spin ladder (1D-SL) regime takes place at temperature T=T*. For T<T* stripe formation results in the quantum 1D transport with the characteristic inelastic length L_phi being fully controlled by the magnetic correlation length xi_m of the even-chain SL, whereas for T> T* the 2D quantum transport is realized with L_\phi governed by the 2D-H correlations L_phi=xi_m=exp(J/T)$. Therefore, the pseudogap found in underdoped (p<p_opt) high Tc's is the spin-gap Delta(p) in even-chain 1D-SL.