Stationary properties of high-critical-temperature proximity effect Josephson junctions

Delin, K. A.; Kleinsasser, A. W.

doi:10.1088/0953-2048/9/4/001

Cited by 204 publications

(129 citation statements)

References 145 publications

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“…2 data from a YBa 2 Cu 3 O 7-d planar SNS junction with the same value of d/ξ ND plotted against reduced temperature 25 : there is excellent agreement between the data consistent with ideal SNS behaviour, but the very different values of I C R N /∆ provides evidence that the two systems are rather different electronically. If we take the modal value of ∆ reported in the literature (5meV) [6][7][8][9] , I C R N for the MgB 2 junction is close to the direct prediction of de Gennes, 24 whereas for the YBa 2 Cu 3 O 7-d junctions it is much lower, implying strong gap suppression in the electrodes. 25 Direct calculation of ξ ND ( (hv f l / (4πkT c )) 0.5 ) is difficult given the uncertainty of the mean-free path (l), but using a value of 4.7x10 5 for the Fermi velocity (v f ) 2 , our value for ξ ND implies that l is of the order of 5nm.…”

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confidence: 79%

Planar superconductor-normal-superconductor Josephson junctions in MgB2

Burnell

Kang

Lee³

et al. 2001

Applied Physics Letters

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Since the discovery of superconductivity in MgB 2 1 considerable progress has been made in determining the physical properties of the material, which are promising for bulk conductors 2-5 . Tunneling studies [6][7][8][9] show that the material is reasonably isotropic and has a well-developed s-wave energy gap (∆), implying that electronic devices based on MgB 2 could operate close to 30K. Although a number of groups have reported the formation of thin films by post-reaction of precursors 10-14 , heterostructure growth is likely to require considerable technological development, making single-layer device structures of most immediate interest. MgB 2 is unlike the cuprate superconductors in that grain boundaries do not form good Josephson junctions, and although a SQUID based on MgB 2 nanobridges has been fabricated 15 , the nanobridges themselves do not show junction-like properties. Here we report the successful creation of planar MgB 2 junctions by localised ion damage in thin films. The critical current (I C ) of these devices is strongly modulated by applied microwave radiation and magnetic field. The product of the critical current and normal state resistance (I C R N ) is remarkably high, implying a potential for very high frequency applications.Our film deposition technique has been described elsewhere. 12 Briefly, B films were deposited at room temperature on to (0001) sapphire substrates by electron beam evaporation and then ex-situ annealed in a Mg vapour at 850°C for 30 minutes to produce MgB 2 films with a final thickness of 100nm and a critical temperature (T C ) of 36K. We deposited a 20nm Au film onto the films by dc magnetron sputtering in order to protect the MgB 2 from contact with water during subsequent processing. Tracks and contact pads were patterned in the bilayer film using standard photolithography and broad beam Ar-ion milling. The T C of the patterned tracks was approximately 35K. In order to fabricate the junctions, the film was then transferred to a focused ion beam system (FIB) (Philips-FEI Inc. FIB 200). Chips were wirebonded to enable the resistance of the tracks to be monitored during the FIB milling process. 16 The barrier was defined by writing 50nm wide cuts across the width of tracks using a 4pA 30kV Ga ion beam. The depth of the cut was calibrated by comparing the cut time to that required to completely sever a track; since the Au mills more than order of magnitude faster than the MgB 2 it could be ignored in calibrating the cut depth. Compared to other materials used to fabricate SNS junctions using this technique, 17 MgB 2 offers the advantage of a relatively low milling rate and hence excellent depth control due to the low atomic mass of its constituents and high melting point.The devices were measured in dip probes placed in 4 He storage dewars. The probes are equipped with coils to provide a magnetic field perpendicular to the substrate plane, and with a microwave antenna. The inset to Fig. 1 shows the resistance against temperature for two tracks on the same substrate,...

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confidence: 79%

Planar superconductor-normal-superconductor Josephson junctions in MgB2

Burnell

Kang

Lee³

et al. 2001

Applied Physics Letters

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“…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.…”

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confidence: 99%

Quantitative model for theICRproduct ind-wave Josephson junctions

et al. 2007

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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

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“…There is presently a growing interest in the development of superconducting bilayers S 1 -S 2 for a number of practical applications, like tunnel junctions for X-ray detection [1][2][3][4] , transition edge sensors [1][2]5 and Josephson junctions 6 . When designing such devices, it is often necessary to adjust and predict the bilayer transition temperature T c .…”

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confidence: 99%

Critical temperature of superconducting bilayers: Theory and experiment

Brammertz

Golubov

Verhoeve

et al. 2002

Applied Physics Letters

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A generalized model for the critical temperature T c of superconducting bilayers is presented, which is valid with no restrictions to film thicknesses, T c of the layers and interface resistivity. The model is verified experimentally on a series of Nb-Al and Ta-Al bilayers with Nb, Ta layer thicknesses of 100 nm and Al layer thicknesses ranging from 5 nm to 200 nm. Excellent agreement between theory and experiment was found for the energy gap and the T c of bilayers. The results are important for designing practical superconducting devices.

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Stationary properties of high-critical-temperature proximity effect Josephson junctions

Cited by 204 publications

References 145 publications

Planar superconductor-normal-superconductor Josephson junctions in MgB2

Planar superconductor-normal-superconductor Josephson junctions in MgB2

Quantitative model for theICRproduct ind-wave Josephson junctions

Critical temperature of superconducting bilayers: Theory and experiment

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