Nature of c-axis coupling in underdoped Bi2Sr2CaCu2O8 with varying degrees of disorder

TL;DR

This study investigates how disorder affects the c-axis Josephson plasma resonance in underdoped Bi2Sr2CaCu2O8, revealing that disorder reduces superfluid density mainly through pair-breaking, with temperature dependence consistent across disorder levels.

Contribution

It provides new insights into the impact of pointlike disorder on c-axis coupling and superfluid density in underdoped cuprates, emphasizing pair-breaking effects over quantum phase fluctuations.

Findings

Zero temperature plasma frequency decreases with increased disorder.

Temperature dependence of JPR frequency remains consistent across disorder levels.

c-axis superfluid density reduction is mainly due to impurity-induced pair-breaking.

Abstract

The dependence of the Josephson Plasma Resonance (JPR) frequency in heavily underdoped Bi2Sr2CaCu2O8+\delta on temperature and controlled pointlike disorder, introduced by high-energy electron irradiation, is cross-correlated and compared to the behavior of the ab-plane penetration depth. It is found that the zero temperature plasma frequency, representative of the superfluid component of the c-axis spectral weight, decreases proportionally with T_c when the disorder is increased. The temperature dependence of the JPR frequency is the same for all disorder levels, including pristine crystals. The reduction of the c-axis superfluid density as function of disorder is accounted for by pair-breaking induced by impurity scattering in the CuO2 planes, rather than by quantum fluctuations of the superconducting phase. The reduction of the c-axis superfluid density as function of temperature follows a T^{2}--law and is accounted for by quasi-particle hopping through impurity induced interlayer states.