Tailoring of high-Tc Josephson junctions by doping their electrodes

Schneider, Claudia; Schulz, Robert; Goetz, B.; Schmehl, A.; Bielefeldt, H.; Hilgenkamp, H.; Mannhart, J.

doi:10.1063/1.124534

Cited by 34 publications

(22 citation statements)

References 27 publications

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“…For the Ca-doped YBCO epitaxial films, macroscopic spatial variation in the STS at a length scale of ϳ50 nm was observed, which correlated with the dimension of the growth islands according to images of atomic force microscopy [22], while the STS within each island were spatially homogeneous, as exemplified in Fig. 1(c).…”

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confidence: 68%

“…9 82.0 6 1.5 K [8,22]. The spectra of YBCO single crystals were taken primarily with the quasiparticles tunneling along three axes: the antinode axes ͕100͖ or ͕010͖, the nodal axis ͕110͖, and the c axis ͕001͖; while those of the pure and Ca-YBCO films were taken along the c axis.…”

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confidence: 99%

“…Thus, under the premise that the spectra are spatially homogeneous well beyond the coherence length and mean free path, we suggest that the long-range and symmetric subgap peaks in overdoped YBCO represent supporting evidence for doping-induced variations in the pairing symmetry. The substantial s-pairing component ͑.20%͒ may also contribute to the significant enhancement in the 087003-2 087003-2 VOLUME 87, NUMBER 8 critical current of bi-crystal Josephson junctions and polycrystalline samples based on the Ca-YBCO [22].…”

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Evidence of Doping-Dependent Pairing Symmetry in Cuprate Superconductors

et al. 2001

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Scanning tunneling spectroscopy studies reveal long-range spatial homogeneity and predominantly d x 2 2y 2 -pairing spectral characteristics in under-and optimally doped YBa 2 Cu 3 O 72d superconductors, whereas STS on YBa 2 ͑Cu 0.9934 Zn 0.0026 Mg 0.004 ͒ 3 O 6.9 exhibits microscopic spatial modulations and strong scattering near the Zn or Mg impurity sites, together with global suppression of the pairing potential. In contrast, in overdoped ͑Y 0.7 Ca 0.3 ͒Ba 2 Cu 3 O 72d , ͑d x 2 2y 2 1 s͒-pairing symmetry is found, suggesting significant changes in the superconducting ground state at a critical doping value. A possible consequence of a QCP is the dopingdependent pseudogap phenomenon [13], which may represent a precursor for superconductivity in the cuprates [13]. Early experiments on the Bi-2212 system reported a measured energy gap D ‫ء‬ ͑p͒ that increased monotonically with decreasing p and was nearly independent of temperature [14][15][16][17][18][19]. However, the low-temperature spectra of the optimally doped and underdoped Bi-2212 appeared to consist of a sharp peak feature on top of a broad "hump." Recent bulk measurements on Bi-2212 mesas [20] demonstrated strong temperature dependence associated with the sharp peak, which vanished at the superconducting transition temperature T c , while the hump feature persisted well above T c . The coexistence of these two gaplike features in the superconducting state has been attributed to a different physical origin associated with each gap [20,21].In this work, we address some of these issues via studies of the directional and spatially resolved quasiparticle tunneling spectra on the YBa 2 Cu 3 O 72d (YBCO) with a range of doping levels. The doping dependence of the pairing symmetry, pairing potential, and spatial homogeneity is derived from these studies.The samples used in this investigation included three optimally doped YBCO single crystals with T c 92.9 6 0.1 K, three underdoped YBCO single crystals with T c 60.0 6 1.5 K, one underdoped YBCO c-axis film with T c 85.0 6 1.0 K, two overdoped ͑Y 0.7 Ca 0.3 ͒Ba 2 Cu 3 O 72d (Ca-YBCO) c-axis films [22] with T c 78.0 6 2.0 K, and one optimally doped single crystal containing small concentrations of nonmagnetic impurities, YBa 2 ͑Cu 0.9934 Zn 0.0026 Mg 0.004 ͒ 3 O 6.9 [(Zn,Mg)-YBCO], with T c 82.0 6 1.5 K [8,22]. The spectra of YBCO single crystals were taken primarily with the quasiparticles tunneling along three axes: the antinode axes ͕100͖ or ͕010͖, the nodal axis ͕110͖, and the c axis ͕001͖; while those of the pure and Ca-YBCO films were taken along the c axis. All samples except (Zn,Mg)-YBCO are twinned. The surface was prepared by chemical etching [23,24], and samples were kept either in high-purity helium gas or under high vacuum at all times. Our surface preparation has the advantage of terminating the YBCO top surface at the CuO 2 plane by chemically passivating the layer while retaining the bulk properties of the constituent elements [23,24], thus yielding reproducible spectra for samples of the same 0...

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Evidence of Doping-Dependent Pairing Symmetry in Cuprate Superconductors

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“…2 Recently it has been demonstrated that improvement in the critical currents attainable in the technologically promising superconductor YBa 2 Cu 3 O 7−␦ can be achieved by doping the grain boundaries with calcium. [3][4][5] If grain boundary critical currents are to be further increased, a better understanding of the mechanisms by which calcium alters the grain boundary properties is needed. Presently it is thought that the calcium alters the carrier density and the amount of trapped charge at the boundary, changing the form of the potential barrier.…”

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Capacitance measurements on grain boundaries in Y1−xCaxBa2Cu3O7−δ

Ransley¹,

McBrien²,

Burnell³

et al. 2004

Phys. Rev. B

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The capacitance of 24°͓001͔ tilt calcium doped Y 1−x Ca x Ba 2 Cu 3 O 7−␦ grain boundaries has been measured for thin films with x in the range 0.0-0.3. The capacitance was determined from the hysteresis in the I-V characteristic. By measuring the capacitance as a function of the voltage across the junctions it was possible to observe the contribution of both parasitic substrate capacitance and heating to the hysteresis. These effects enable the determination of the intrinsic capacitance of the grain boundaries. The effect of thermal noise on the measurement is also assessed, and found to be much less than the observed changes in the capacitance. The capacitance is found to increase as the calcium doping increases: from 0.2 Fm −2 for x = 0.0 to a maximum of 1.2 Fm −2 for x = 0.3. The changes in the capacitance per unit area are observed to be inversely proportional to the corresponding changes in the resistance area product.

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“…17 Recently, Ca-doping of YBCO films has also provided a way to increase I C and to reduce significantly R N of GBJ's. 18,19 On the contrary, a controlled worsening of these parameters is observed when the barrier is modified by electron beam 20 and proton irradiation. 21 However, none of these last studies have been done on GBJ's made on bicrystals.…”

Section: Introductionmentioning

confidence: 95%

Electromagnetic properties andHe+irradiation effects onYBa2
Mulas
¹
,
Quesada
²
,
Navacerrada
³

2000
Phys. Rev. B
18
0
14
0
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We have analyzed the electromagnetic properties of small and long YBa 2 Cu 3 O 7Ϫx grain-boundary Josephson junctions. The Swihart velocity increases with junction width ͑w͒ while the ratio of the relative dielectric constant to the barrier thickness (/t) decreases. We found that the product wϫ/t is approximately constant. These results have been explained in the framework of the filamentary model, where the barrier can be regarded as a disordered dielectric medium with a high density of superconducting filaments. Experiments demonstrate that a controllable variation of these parameters can be achieved by helium irradiation at 80 keV. We give examples of an enhancement of weak-link properties of junctions for doses in the range of 10 13 cm Ϫ2. Raising the dose we can sweep the modification of the weak-link properties from an increase of the junction critical current of about 10% to a severe degradation of the coupling energy of the barrier, although the superconducting properties of the electrodes always worsen gradually.

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Tailoring of high-Tc Josephson junctions by doping their electrodes

Cited by 34 publications

References 27 publications

Evidence of Doping-Dependent Pairing Symmetry in Cuprate Superconductors

Evidence of Doping-Dependent Pairing Symmetry in Cuprate Superconductors

Capacitance measurements on grain boundaries in Y1−xCaxBa2Cu3O7−δ

Electromagnetic properties andHe+irradiation effects onYBa2
Mulas
¹
,
Quesada
²
,
Navacerrada
³

2000
Phys. Rev. B
18
0
14
0
View full text Add to dashboard Cite

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Tailoring of high-Tc Josephson junctions by doping their electrodes

Cited by 34 publications

References 27 publications

Evidence of Doping-Dependent Pairing Symmetry in Cuprate Superconductors

Evidence of Doping-Dependent Pairing Symmetry in Cuprate Superconductors

Capacitance measurements on grain boundaries in Y1−xCaxBa2Cu3O7−δ

Electromagnetic properties andHe+irradiation effects onYBa2Mulas1, Quesada2, Navacerrada3 2000Phys. Rev. B180140View full textAdd to dashboardCite

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Electromagnetic properties andHe+irradiation effects onYBa2
Mulas
¹
,
Quesada
²
,
Navacerrada
³

2000
Phys. Rev. B
18
0
14
0
View full text Add to dashboard Cite