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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

Resistance versus temperature of a Josephson junction with a 20 nm thick LSCO-0.07 barrier obtained using a 100 µA current bias.The top inset shows a schematic cross-section of the junction, and the bottom one is a zoom-in on the resistance below the transition of the YBCO electrodes.
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f1: Resistance versus temperature of a Josephson junction with a 20 nm thick LSCO-0.07 barrier obtained using a 100 µA current bias.The top inset shows a schematic cross-section of the junction, and the bottom one is a zoom-in on the resistance below the transition of the YBCO electrodes.

Mentions: We chose to work with fully epitaxial SS'S thin film junctions of the cuprates that have a conveniently wide temperature range where S' is in the pseudogap regime between the Tc values of S' and S. In this regime, we shall refer to the junctions as SNS junctions, which is the more commonly used term in such a situation. Optimally doped Y Ba2Cu3O7−δ (YBCO) with Tc ≈ 90 K was chosen as the S electrodes, while the S' barrier was chosen to be La2−xSrxCuO4 (LSCO-x) with Tc values of up to about 25 K. A schematic cross-section of a junction is shown in the top inset of Fig. 1. The trilayer film of YBCO/LSCO-x/YBCO was grown epitaxially in-situ by laser ablation deposition on 10 × 10 mm2 wafers of (100) SrTiO3. The trilayer was then patterned by photolithography and Ar ion milling to produce ten base electrodes with their corresponding ramps on the wafer. This was followed by a room temperature deposition of the gold cover electrode, which unlike in our previous ramp junctions26, left the ramp of the base electrode in a highly resistive state, with only a negligible current flow in the a–b plane direction through it for the lack of the high temperature annealing step. This yielded a cross-over junction where the current flows mostly in the c-axis direction via a 5 × 5 µm2 area (defined by a second patterning process) into the gold cover electrode.


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)

Resistance versus temperature of a Josephson junction with a 20 nm thick LSCO-0.07 barrier obtained using a 100 µA current bias.The top inset shows a schematic cross-section of the junction, and the bottom one is a zoom-in on the resistance below the transition of the YBCO electrodes.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Resistance versus temperature of a Josephson junction with a 20 nm thick LSCO-0.07 barrier obtained using a 100 µA current bias.The top inset shows a schematic cross-section of the junction, and the bottom one is a zoom-in on the resistance below the transition of the YBCO electrodes.
Mentions: We chose to work with fully epitaxial SS'S thin film junctions of the cuprates that have a conveniently wide temperature range where S' is in the pseudogap regime between the Tc values of S' and S. In this regime, we shall refer to the junctions as SNS junctions, which is the more commonly used term in such a situation. Optimally doped Y Ba2Cu3O7−δ (YBCO) with Tc ≈ 90 K was chosen as the S electrodes, while the S' barrier was chosen to be La2−xSrxCuO4 (LSCO-x) with Tc values of up to about 25 K. A schematic cross-section of a junction is shown in the top inset of Fig. 1. The trilayer film of YBCO/LSCO-x/YBCO was grown epitaxially in-situ by laser ablation deposition on 10 × 10 mm2 wafers of (100) SrTiO3. The trilayer was then patterned by photolithography and Ar ion milling to produce ten base electrodes with their corresponding ramps on the wafer. This was followed by a room temperature deposition of the gold cover electrode, which unlike in our previous ramp junctions26, left the ramp of the base electrode in a highly resistive state, with only a negligible current flow in the a–b plane direction through it for the lack of the high temperature annealing step. This yielded a cross-over junction where the current flows mostly in the c-axis direction via a 5 × 5 µm2 area (defined by a second patterning process) into the gold cover electrode.

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