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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.


Related in: MedlinePlus

Current versus voltage at 10 K of a Josephson junction with a 20 nm thick LSCO-0.07 barrier.A gold series resistance of 0.3 Ω was subtracted from the data. The inset shows the conductance of this junction at 40 K under 10.7 GHz microwave irradiation, where the Shapiro steps in the corresponding I-V curve are seen as evenly spaced peaks.
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f2: Current versus voltage at 10 K of a Josephson junction with a 20 nm thick LSCO-0.07 barrier.A gold series resistance of 0.3 Ω was subtracted from the data. The inset shows the conductance of this junction at 40 K under 10.7 GHz microwave irradiation, where the Shapiro steps in the corresponding I-V curve are seen as evenly spaced peaks.

Mentions: A typical I-V curve at 10 K of this type of Josephson junction is shown in Fig. 2. This curve shows that the junction has a critical current of 0.55 mA as measured by a 5 µV criterion. It also exhibits a resistively shunted junction (RSJ) behavior at higher bias with a normal resistance of 0.8 Ω. The IcRN product of the junction is therefore equal to 0.44 meV which is typical of Josephson junctions in the cuprates27. The inset of Fig. 2 depicts a conductance spectrum of this Josephson junction at 40 K under 10.7 GHz microwave irradiation, showing the AC Josephson effect. The evenly spaced peaks in the curve are due to Shapiro steps in the I-V curve at a somewhat larger than the expected spacing of ΔV = hν/2e due to the series resistance of about 0.3 Ω of the gold cover electrode. On a wafer with 10 junctions, the spread of the measured critical current values was about ±30%. In the following measurements of Ic versus T on each wafer with a given barrier thickness and doping level, we had chosen to work on the junction whose critical current value is closest to the average value obtained on that wafer.


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)

Current versus voltage at 10 K of a Josephson junction with a 20 nm thick LSCO-0.07 barrier.A gold series resistance of 0.3 Ω was subtracted from the data. The inset shows the conductance of this junction at 40 K under 10.7 GHz microwave irradiation, where the Shapiro steps in the corresponding I-V curve are seen as evenly spaced peaks.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Current versus voltage at 10 K of a Josephson junction with a 20 nm thick LSCO-0.07 barrier.A gold series resistance of 0.3 Ω was subtracted from the data. The inset shows the conductance of this junction at 40 K under 10.7 GHz microwave irradiation, where the Shapiro steps in the corresponding I-V curve are seen as evenly spaced peaks.
Mentions: A typical I-V curve at 10 K of this type of Josephson junction is shown in Fig. 2. This curve shows that the junction has a critical current of 0.55 mA as measured by a 5 µV criterion. It also exhibits a resistively shunted junction (RSJ) behavior at higher bias with a normal resistance of 0.8 Ω. The IcRN product of the junction is therefore equal to 0.44 meV which is typical of Josephson junctions in the cuprates27. The inset of Fig. 2 depicts a conductance spectrum of this Josephson junction at 40 K under 10.7 GHz microwave irradiation, showing the AC Josephson effect. The evenly spaced peaks in the curve are due to Shapiro steps in the I-V curve at a somewhat larger than the expected spacing of ΔV = hν/2e due to the series resistance of about 0.3 Ω of the gold cover electrode. On a wafer with 10 junctions, the spread of the measured critical current values was about ±30%. In the following measurements of Ic versus T on each wafer with a given barrier thickness and doping level, we had chosen to work on the junction whose critical current value is closest to the average value obtained on that wafer.

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