Quantitative model for theICRproduct ind-wave Josephson junctions

Abstract

We study theoretically the Josephson effect in d-wave superconductor/diffusive normal metal/insulator/ diffusive normal metal/d-wave superconductor ͑D/DN/I/DN/D͒ junctions. This model aims to describe practical junctions in high-T C cuprate superconductors, in which the product of the critical Josephson current ͑I C ͒ and the normal state resistance ͑R͒ ͑the so-called I C R product͒ is very small compared to the prediction of the standard theory for clean d-wave superconductor/insulator/d-wave superconductor ͑DID͒ junctions. We show that the I C R product in D/DN/I/DN/D junctions can be much smaller than that in DID junctions. The proposed theory describes the behavior of I C R products quantitatively in high-T C cuprate junctions. DOI: 10.1103/PhysRevB.76.052508 PACS number͑s͒: 74.20.Rp, 74.50.ϩr, 74.70.Kn Josephson effect in high-T C superconductors has attracted much attention 1,2 because of its potential applications in future technologies. 3 In particular, applications in electronics, such as the single-flux quantum devices, are extremely promising, since the operating frequency is proportional to the product of the critical Josephson current ͑I C ͒ and the normal state resistance ͑R͒ ͑the so-called I C R product͒ which is approximately proportional to the superconductivity critical temperature. 4 However, almost all experimental data for high-T C Josephson junctions fabricated so far have shown I C R values much smaller than those predicted by the standard theory, irrespective of what kind of junctions they are. 5,6 This strongly suggests that the interfaces in the cuprates are intrinsically pair breaking. Several models were proposed which treat this issue. 7-10 However, the situation has not been described so far in a quantitative manner.One possibility addressed in the present Brief Report and not investigated before is that superconductivity is destroyed near the interface in d-wave superconductor/insulator/ d-wave superconductor ͑DID͒ junctions, where diffusive normal metal ͑DN͒ regions are induced. Thus, DID junctions turn into d-wave superconductor/diffusive normal metal/ insulator/diffusive normal metal/d-wave superconductor ͑D/ DN/I/DN/D͒ junctions ͑see Fig. 1͒. In these junctions, I C R product can be much smaller than that in DID junctions. In this Brief Report, we will explore this possibility and provide a quantitative model which is compared to the experimental data.The Josephson effect is a phase-sensitive phenomenon and thus depends strongly on a superconducting pairing symmetry. 1,2,11 In DID junctions, nonmonotonic temperature dependence of critical current 12-16 occurs due to the formation of midgap Andreev resonant states ͑MARSs͒ at the interface. 17 The MARSs stem from sign change of pair potentials of d-wave superconductors. 18 It was also predicted that MARSs strongly enhance the Josephson current at low temperatures. 13 On the other hand, in Josephson junctions with DN, the role of the MARSs changes.In superconductor/diffusive normal metal/superconductor

Anomalous temperature dependence of the stationary Josephson tunnel current in junctions between d-wave superconductors

“…Here, d is the thickness of dirty layers coating the electrodes, and l the quasiparticle mean free path. A similar model was studied by another group [45], with the same conclusions being made. If the roughness is weak, the interplay between the proximity effect at the boundary with the normal-state diffusive layer and the midgap resonance states may lead to a nonmonotonic ( ) J I T dependence [26,42,43,[46][47][48][49].…”

Critical current of a granular d-wave superconductor

“…Notethat for > /4, the sign of the current changes. Thus, in this case the junction isformed [30]. In order to analyze the Josephson critical current of granular d-wave superconductor, we consider Meilikhov's model, in which, the weak link between grains is formed in the region of plane segments [36].…”

High-T c Josephson junctions

“…On the other hand, the nature of the high-T c materials results in new aspects like anisotropy of the parameters with crystal orientation, pairing symmetry (d-wave instead of conventional s-wave), high penetration depth and small coherence length. Tanaka and Kashiwaya (1997), Golubov and Tafuri (2000), Yokoyama et al (2007), and references therein. Another physics is related to high-T c cuprate superconductors because they have an atomically layered structure of superconducting sheets S and S′ separated by insulating or normal conducting layers with different coupling strengths t and t′, respectively (see Fig.…”