Interplane charge dynamics in high-temperature superconductors; Charge confinement and spin gap

Abstract

We have studies optical and transport properties of the prototypical high-Tc system La2−xSrxCuO4 in the direction perpendicular to the CuO2 planes (c-axis direction). In the normal state, it is found that the c-axis spectral weight is suppressed over a wide energy range. This is a demonstration of “charge confinement” in the real material which has been proposed theoretically by Anderson. Upon reducing temperature the low-energy spectral weight of the underdoped compound is further reduced, due perhaps to “spin gap” effect. The suppressed spectral weight results in completely different out-of-plane charge transport in the normal state and leads to the appearance of a superconducting plasma edge within the gap region in the superconducting state.