Scaling spontaneous fluctuations in high-Tc superconductor films

Kiss, L.B.; Svedlindh, Peter; Lundgren, L.; Hudner, J.; Ohlsén, H.; Stolt, Lars; Gingl, Zoltán

doi:10.1016/0921-4526(91)90003-w

Cited by 13 publications

(7 citation statements)

References 15 publications

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“…3,4 This includes the onset of the several stages of the transition, the intergrain critical currents, the effect of magnetic fields, the role of inhomogeneities and other kinds of disorder, and the dynamics of the vortex motion in the material. 5 Noise associated with conductivity fluctuations ͑or resistance fluctuations͒ 6,7 has the following characteristic:…”

Section: B Noise In High-t C Superconducting Materialsmentioning

confidence: 99%

“…͑a͒ No noise is found in the superconducting state well below T c ; ͑b͒ in the normal state near T c , the noise is large compared to metal-insulator composites; and ͑c͒ the noise was reported to increase in the transition region. 5 The effect of a defect can be modeled as a two-level fluctuator ͑TLF͒ moving between two energy states separated by an energy barrier. 8 Transitions between the two states generate a random telegraph signal ͑RTS͒.…”

Section: B Noise In High-t C Superconducting Materialsmentioning

confidence: 99%

See 1 more Smart Citation

Noise characteristics and detectivity of YBa2Cu3O7 superconducting bolometers: Bias current, frequency, and temperature dependence

Fardmanesh

Rothwarf

Scoles

1996

Journal of Applied Physics

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Meander line patterned infrared detectors, with values of resistance R onset at the onset temperature T c onset of 3-5 k⍀, were fabricated from YBa 2 Cu 3 O 7Ϫx superconducting material on MgO and SrTiO 3 crystalline substrates. Noise voltages from the samples were measured versus bias current, radiation modulation frequency, and temperature, in both the normal and superconducting states. Four major types of voltage noise were identified according to where they occurred in temperature relative to T c onset and the zero resistance temperature T c zero , and their dependence on frequency and bias current. They were also associated with the granularity of the superconducting film, which is related to the substrate material used. From these observations a specific cause for each type of noise is suggested. The results are as follows. ͑i͒ In the normal state with temperature T Ͼ T c onset , noise with a magnitude that is consistent with thermal ͑Johnson͒ noise is seen, but it depends linearly on bias current above a threshold value, at low frequencies. The suggested noise source is conductivity fluctuations due to Cooper pairs. ͑ii͒ Noise was found to occur below T c zero in granular films. With increasing bias current its magnitude increases, and it shifts to a lower temperature range; however, the noise magnitude becomes constant as the current goes to zero. It is weakly dependent on frequency above 400 Hz. Suggested cause is voltage fluctuations in superconductor-normal-superconductor junctions at grain boundaries. ͑iii͒ This noise also occurs below T c zero with peaks at various temperatures. With increasing bias current the peaked noise spreads to lower temperatures, but the noise goes to zero as the bias current goes to zero. Its suggested cause is magnetic flux tube motion. ͑iv͒ This noise occurs between T c onset and T c zero and is present in all samples, but lowest on samples prepared on SrTiO 3 substrates. Its suggested cause is fluctuations in the volume fraction of the superconducting phase along the current path. While the measured detectivity D* of our samples at a wavelength of 20 m was only 10 6 cm Hz 1/2 /W, engineering changes can be expected to raise the value to above 10 10 cm Hz 1/2 /W.

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Section: B Noise In High-t C Superconducting Materialsmentioning

confidence: 99%

Section: B Noise In High-t C Superconducting Materialsmentioning

confidence: 99%

Noise characteristics and detectivity of YBa2Cu3O7 superconducting bolometers: Bias current, frequency, and temperature dependence

Fardmanesh

Rothwarf

Scoles

1996

Journal of Applied Physics

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“…At the same time, relative fluctuations V 2 /V 2 decrease with increasing temperature. This means that, in this case, the percolation model of fluctuations [22][23][24], which predicts an increase in intensity and scaling behaviour of relative fluctuations, is inapplicable. Figure 4 shows dependences V 2 (I ) at B 0 = 5 mT and T ≈ 78 K. The linearity of these dependences means that the voltage fluctuations in the resistive state are not related to resistance fluctuations, since in this case it would be…”

Section: Resultsmentioning

confidence: 99%

“…In four-probe measurements, fluctuations of the magnetic flux moving within a superconductor are also observed (see, e.g., [20,21]). However, resistance fluctuations are observed much more frequently, especially in granulated superconductors [22][23][24][25][26][27][28][29][30].…”

Section: Introductionmentioning

confidence: 99%

Voltage fluctuations in granular superconductors in the perpendicular configuration

Gerashchenko

2003

Supercond. Sci. Technol.

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The spectral density of voltage fluctuations in granular YBa2Cu3O7−δ superconductors in the perpendicular configuration has been studied in the flux flow mode. It has been found that, in this case, the 1/f-voltage noise observed depends weakly on temperature and is associated with motion of a magnetic flux in the superconductor. A comparison of the data obtained with the results of previous measurements in parallel configuration has shown that voltage noise is produced by a single common source, which is presumably associated with self-organization of the critical state in granular superconductors.

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“…In a different situation, when weak links do not play an important role, the noise may be predominantly generated by fluxoids motion. [4,5,16,17,18]. It is interesting to notice that series of random steps having the same sign when the resistance of the specimen increases or decreases gives rise in general to a 1/f 2 component, while random steps of random signs may give rise to a 1/f spectrum under suitable conditions for their distribution.…”

Section: Resultsmentioning

confidence: 99%

Current noise in high Tc granular superconductors under non-stationary conditions of current and magnetic field

et al. 2003

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We present a set of experimental results concerning the power spectrum of current noise, detected on a granular high Tc superconductor submitted either to a slowly varying magnetic field or to a varying current intensity. Experiments were performed on a YBCO specimen suitably treated in order to weaken the weak links without affecting the oxygen content of grains. The weakening of the intergrain region allowed the use of very small magnetic fields and currents to induce the resistive transition of the specimen and to observe current noise. The induced noise is of the 1/f 2 type and will be interpreted in terms of two different models. One of the model is based on the enhancement of the noise due to the clustering of the resistive transition of the weak links, produced by correlation effects related to the strong nonlinearity of their Josephson type I-V characteristics. This model has been the object of a computer simulation based on a 3D-network of Josephson-like elements and seems suitable to explain the noise produced by current variation. The second model explains the excess noise as produced by discontinuous penetration of the magnetic flux inside the intergrain region. This discontinuity is related to the field screening effect of rings made of several superconducting weak links connecting different grains, which are alternatively broken and restored by the current induced during flux variation, and seems suitable to explain the larger noise produced by a varying magnetic field.

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Scaling spontaneous fluctuations in high-Tc superconductor films

Cited by 13 publications

References 15 publications

Noise characteristics and detectivity of YBa2Cu3O7 superconducting bolometers: Bias current, frequency, and temperature dependence

Noise characteristics and detectivity of YBa2Cu3O7 superconducting bolometers: Bias current, frequency, and temperature dependence

Voltage fluctuations in granular superconductors in the perpendicular configuration

Current noise in high Tc granular superconductors under non-stationary conditions of current and magnetic field

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