Spin-fluctuation gating in the c-axis non-Drude conductivity of the high Tc cuprates

An ideal antiferromagnetic (AF) ordering of the spins of the CuO layers of an underdoped cuprate prevents the low energy tunneling of the charge carriers between the layers. In order to obtain a non-vanishing c-axis conductivity (σ_c), we invoke ground state fluctuations of the spin system. These provide a frequency-dependent gating effect by changing the direction of the AF order parameter within one layer relative to that in a neighboring layer, thereby permitting some tunneling. The calculated σ_c compares favorably with experimental data in a) being small and b) having a weak frequency dependence of distinctly non-Drude form.