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Pairing and the phase diagram of the normal coherence length ξN(T, x) above Tc of La(2-x)Sr(x)CuO4 thin films probed by the Josephson effect.

Kirzhner T, Koren G - Sci Rep (2014)

Bottom Line: The long range proximity effect in high-Tc c-axis Josephson junctions with a high-Tc barrier of lower Tc is still a puzzling phenomenon.It leads to supercurrents in junctions with much thicker barriers than would be allowed by the conventional proximity effect.This indicates that a possible origin of the long range proximity effect in the cuprate barrier is the conjectured pre-formed pairs in the pseudogap regime, which increase the length scale over which superconducting correlations survive in the seemingly normal barrier.

View Article: PubMed Central - PubMed

Affiliation: Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel.

ABSTRACT
The long range proximity effect in high-Tc c-axis Josephson junctions with a high-Tc barrier of lower Tc is still a puzzling phenomenon. It leads to supercurrents in junctions with much thicker barriers than would be allowed by the conventional proximity effect. Here we measured the T - x (Temperature-doping level) phase diagram of the barrier coherence length ξN(T, x), and found an enhancement of ξN at moderate under-doping and high temperatures. This indicates that a possible origin of the long range proximity effect in the cuprate barrier is the conjectured pre-formed pairs in the pseudogap regime, which increase the length scale over which superconducting correlations survive in the seemingly normal barrier. In more details, we measured the supercurrents Ic of Superconducting - Normal - Superconducting SNS c-axis junctions, where S was optimally doped Y Ba2Cu3O(7-δ) below Tc (90 K) and N was La(2-x)Sr(x)CuO4 above its Tc (<25 K) but in the pseudogap regime. From the exponential decay of Ic(T) ∝ exp[-d/ξN(T)], where d is the barrier thickness, the ξN(T) values were extracted. By repeating these measurements for different barrier doping levels x, the whole phase diagram of ξN(T, x) was obtained.

No MeSH data available.


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Critical current as a function of temperature of two Josephson junctions on two different wafers with LSCO-0.07 barrier thicknesses of 20 nm and 12 nm.
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f3: Critical current as a function of temperature of two Josephson junctions on two different wafers with LSCO-0.07 barrier thicknesses of 20 nm and 12 nm.

Mentions: Next we focus on the temperature dependence of the critical currents which were extracted from the I-V curves using a 5 µV criterion. Fig. 3 shows the temperature dependence of the critical currents in two representative Josephson junctions with LSCO-0.07 barriers on two different wafers. One with a 20 nm thick barrier and the other with a thinner 12 nm thick barrier. At temperatures above 40–50 K, when the critical currents are small, they decay versus temperature as a (Tc − T)2 power law as predicted by the De-Gennes dirty limit proximity effect formula28. At lower temperatures, as the supercurrents increase, the I-V curves deviate from the weak-link RSJ model and start to show a strong-link flux flow behavior which changes the power law temperature dependence. This may be due to the self field effect when the width of the junction w becomes larger than the Josephson penetration depth λJ. A critical current of about 1.5 mA at 40 K with the 12 nm thick barrier, corresponds to a Josephson penetration depth λJ of which is of the order of the width of our junctions (w = 5 µm).


Pairing and the phase diagram of the normal coherence length ξN(T, x) above Tc of La(2-x)Sr(x)CuO4 thin films probed by the Josephson effect.

Kirzhner T, Koren G - Sci Rep (2014)

Critical current as a function of temperature of two Josephson junctions on two different wafers with LSCO-0.07 barrier thicknesses of 20 nm and 12 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4150101&req=5

f3: Critical current as a function of temperature of two Josephson junctions on two different wafers with LSCO-0.07 barrier thicknesses of 20 nm and 12 nm.
Mentions: Next we focus on the temperature dependence of the critical currents which were extracted from the I-V curves using a 5 µV criterion. Fig. 3 shows the temperature dependence of the critical currents in two representative Josephson junctions with LSCO-0.07 barriers on two different wafers. One with a 20 nm thick barrier and the other with a thinner 12 nm thick barrier. At temperatures above 40–50 K, when the critical currents are small, they decay versus temperature as a (Tc − T)2 power law as predicted by the De-Gennes dirty limit proximity effect formula28. At lower temperatures, as the supercurrents increase, the I-V curves deviate from the weak-link RSJ model and start to show a strong-link flux flow behavior which changes the power law temperature dependence. This may be due to the self field effect when the width of the junction w becomes larger than the Josephson penetration depth λJ. A critical current of about 1.5 mA at 40 K with the 12 nm thick barrier, corresponds to a Josephson penetration depth λJ of which is of the order of the width of our junctions (w = 5 µm).

Bottom Line: The long range proximity effect in high-Tc c-axis Josephson junctions with a high-Tc barrier of lower Tc is still a puzzling phenomenon.It leads to supercurrents in junctions with much thicker barriers than would be allowed by the conventional proximity effect.This indicates that a possible origin of the long range proximity effect in the cuprate barrier is the conjectured pre-formed pairs in the pseudogap regime, which increase the length scale over which superconducting correlations survive in the seemingly normal barrier.

View Article: PubMed Central - PubMed

Affiliation: Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel.

ABSTRACT
The long range proximity effect in high-Tc c-axis Josephson junctions with a high-Tc barrier of lower Tc is still a puzzling phenomenon. It leads to supercurrents in junctions with much thicker barriers than would be allowed by the conventional proximity effect. Here we measured the T - x (Temperature-doping level) phase diagram of the barrier coherence length ξN(T, x), and found an enhancement of ξN at moderate under-doping and high temperatures. This indicates that a possible origin of the long range proximity effect in the cuprate barrier is the conjectured pre-formed pairs in the pseudogap regime, which increase the length scale over which superconducting correlations survive in the seemingly normal barrier. In more details, we measured the supercurrents Ic of Superconducting - Normal - Superconducting SNS c-axis junctions, where S was optimally doped Y Ba2Cu3O(7-δ) below Tc (90 K) and N was La(2-x)Sr(x)CuO4 above its Tc (<25 K) but in the pseudogap regime. From the exponential decay of Ic(T) ∝ exp[-d/ξN(T)], where d is the barrier thickness, the ξN(T) values were extracted. By repeating these measurements for different barrier doping levels x, the whole phase diagram of ξN(T, x) was obtained.

No MeSH data available.


Related in: MedlinePlus