Origin of intrinsic Josephson coupling in the cuprates and its relation to order parameter symmetry: An incoherent hopping model

Abstract

Experiments on the cuprate superconductors demonstrate that these materials may be viewed as a stack of Josephson junctions along the direction normal to the CuO 2 planes (the c-axis). In this paper, we present a model which de-

Quantum fluctuations and thec-axis optical conductivity of high-Tcsuperconductors

“…Strong scattering the barrier region (i.e. non-momentum-conserving hopping) [9][10][11] or 'occupation modulated hopping' [24] would invalidate our results. We will argue below that the close correspondence between our results and data suggests that the usual band theory form of the hopping is the correct one.…”

“…The observed σ c for optimally doped and overdoped materials provides evidence against the alternative explanation of the c-axis conductivity advanced in [9][10][11]. In these works, the weak frequency dependence of σ c at T > T c is attributed to a strongly momentum nonconserving interplane coupling t ⊥ (p, p ′ ), due physically to strong scattering in the interplane barrier layers, rather than to a large value of an in-plane electron scattering rate Γ.…”

“…4 (arbitrary interplane interactions are allowed). Different hopping terms, such as those considered in [9][10][11]24] would lead to different results, as noted in [11,24].…”

“…In this paper we assume it has the usual band theory form, namely an interplane hopping which conserves in-plane momentum. A large literature exists in which the anomalous properties of the c-axis conductivity are attributed to a highly non-trivial interplane coupling, in which passage from one plane to another involves a strong scattering from some excitation or defect which resides between planes and does not couple to in-plane electron motion: see, for example, [9][10][11] and references therein. As discussed in section VI, we believe there is substantial experimental evidence against this proposal.…”

Polarons in axial transport in single-layer high-Tc superconductors

“…There are two basic prerequisites for superconductivity: pairing and longrange phase coherence, as secured by the interlayer coupling [2]. While pairing has been interpreted in terms of either phononic or nonphononic mechanisms [3,4], the interlayer coupling has been regarded as Josephson tunnelling [5], resonant tunnelling [6], or as a charge transfer (CT) between relevant atomic and molecular orbitals [7]. A path-integral analysis has shown that a (coherent) axial transport may result from the interaction of fermionic excitations with double-well potentials associated with apex oxygens [8].…”