Crossover from Thermal Activation to Quantum Interlayer Transport at the Superconducting Transition Temperature of Bi-2212

TL;DR

This study investigates how interlayer transport in Bi-2212 changes from thermal activation to quantum tunneling at the superconducting transition, revealing doping-dependent mechanisms involving quasiparticles and Cooper pairs.

Contribution

It provides detailed experimental evidence of a crossover in interlayer transport mechanisms at T_c and highlights doping-dependent changes in the dominant transport processes.

Findings

Crossover from thermal activation to quantum tunneling at T_c

Transport mechanism shifts from quasiparticle tunneling to Cooper pair contribution with underdoping

Interlayer transport characteristics depend on doping level

Abstract

We perform a detailed study of temperature, bias and doping dependance of interlayer transport in the layered high temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. We observe that the shape of interlayer characteristics in underdoped crystals exhibit a remarkable crossover at the superconducting transition temperature: from thermal activation-type at $T>T_c$, to almost $T-$independent quantum tunneling-type, at $T<T_c$. Our data indicates that the interlayer transport mechanism may change with doping: from the conventional single quasiparticle tunneling in overdoped, to a progressively increasing Cooper pair contribution in underdoped crystals.