Pseudo-gap behavior in the c-axis conductivity of the underdoped bilayer high Tc cuprates

The frequency-dependent c-axis conductivity, sigma(c)(omega), is calculated using a periodic bilayer model of antiferromagnetically ordered spins, with one bilayer per unit cell. The spin-fluctuation gating mechanism, proposed earlier only for acoustic magnons, yields now a weakly frequency-dependent low-frequency interval followed by a steep rise in sigma(c)(omega), as a function of omega, a kind of shoulder. This theoretical prediction for sigma(c)(omega) can be associated with the experimentally observed ''pscudo-gap'' phenomenon in the underdoped YB2Cu4O8 high T-c crystal. (C) 1998 Elsevier Science Ltd. All rights reserved.