Coherence, incoherence and scaling along the c axis of YBa_2Cu_3O_{6+x}

Abstract

The optical properties of single crystals of YBa_2Cu_3O_{6+x} have been examined along the c axis above and below the critical temperature (T_c) for a wide range of oxygen dopings. The temperature dependence of the optically-determined value of the dc conductivity (σ_{dc}) in the normal state suggests a crossover from incoherent (hopping-type) transport at lower oxygen dopings (x \lesssim 0.9) to more coherent anisotropic three-dimensional behavior in the overdoped (x \approx 0.99) material at temperatures close to T_c. The assumption that superconductivity occurs along the c axis through the Josephson effect yields a scaling relation between the strength of the superconducting condensate (ρ_{s,c}, a measure of the number of superconducting carriers), the critical temperature, and the normal-state c-axis value for σ_{dc} just above T_c; ρ_{s,c} \propto σ_{dc} T_c. This scaling relation is observed along the c axis for all oxygen dopings, as well as several other cuprate materials. However, the agreement with the Josephson coupling model does not necessarily imply incoherent transport, suggesting that these materials may indeed be tending towards coherent behavior at the higher oxygen dopings.

Six pages with four figures and one table

Cited by in corpus (8)

• Electrodynamics of Correlated Electron Materials
• Scaling of the superfluid density in high-temperature superconductors
• The impact of dynamical screening on the phonon dynamics of LaCuO
• Gapped collective charge excitations and interlayer hopping in cuprate superconductors
• The n_s - T_c correlations in granular superconductors
• Effective medium approximation and the complex optical properties of the inhomogeneous superconductor K_{0.8}Fe_{2-y}Se_2
• Optical and photoemission investigation of structural and magnetic transitions in the iron-based superconductor Sr${}_{0.67}$Na${}_{0.33}$Fe${}_2$As${}_2$
• High Temperature Mixed State $c-$Axis Dissipation in Low Carrier Density $Y_{0.54}P{r}_{0.46}B{a}_{2}C{u}_3{O}_{7-\delta }$