| 1. |
- Gershenson, M. E., et al.
(författare)
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Quantum interference effects in percolated metal networks
- 1994
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; , s. 1109-1110
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Konferensbidrag (refereegranskat)abstract
- Quantum corrections (QC) to the resistivity due to weak localization (WL) and electron-electron interaction (EEI) have been measured for percolated metal networks with percolation coherence length z comparable to the quantum length scales-the phase-breaking length L and the thermal diffusion length LT. Far from the percolation metal-insulator transition (MIT) the `macroscopic' disorder is averaged over the quantum lengths (L,LTz) and the QC are of the universal two-dimensional (2D) type with R=R(z), where R(z) is the resistance per square at scales larger than z. A crossover 2D1D in the dimensionality of the QC and the Nyquist phase-braking mechanism is observed near the MIT, where zL,LT
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| 2. |
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| 3. |
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| 4. |
- Davidsson, P, et al.
(författare)
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Vortex mapping on gold covered conventional type II superconductors using the very low temperature tunnelling microscope
- 1994
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194-196:Part 1, s. 375-376
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Tidskriftsartikel (refereegranskat)abstract
- We have used a dilution refrigerator cooled STM for investigating the vortex state in lead-bismuth alloy 4000Aofilms. The vortices were recognized by the decreasing dynamic conductance near the gap voltage when the instrument was operated in its normal feed back mode. A clean surface suitable for tunneling was maintained by a 75Aolayer of gold deposited on top of the sample film. The temperature was kept at 80 mK and magnetic fields between 0 and 0.2 T were used.
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| 5. |
- DJURBERG, C, et al.
(författare)
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RELAXATION OF THE FIELD COOLED MAGNETIZATION IN 2D CU(MN) FILMS
- 1994
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194, s. 303-304
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Tidskriftsartikel (refereegranskat)abstract
- The relaxation of the field cooled magnetisation of a multilayered 2D Cu(Mn) spin glass film has been investigated in a SQUID-magnetometer. The sample is cooled in a constant magnetic field (10 Oe) from a high temperature, where the magnetisation is at equilibrium, to a temperature below the freezing temperature, T(f). At constant temperature, the magnetisation is then found to increase with time at temperatures near T(f), showing an initial decrease followed by an increase at long time scales at intermediate temperatures and only decreases with time at lower temperatures. The behaviour, including the surprising downward relaxation away from the thermodynamic equilibrium magnetisation, is qualitatively interpreted in terms of a spin glass domain model.
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| 6. |
- Han, Shunhui, et al.
(författare)
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Thermodynamic fluctuation in doped BiSrCaCuO superconductors with 110K phase
- 1994
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194-196, s. 1513-1514
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Tidskriftsartikel (refereegranskat)abstract
- The resistivity has been carefully measured for four sintered samples of Pb and Pb/Sb doped Bi-Sr-Ca-Cu-O superconductors with the 110 K phase from zero resistance temperature up to 300 K. The thermodynamical fluctuation have been fitted on the form DELTAsigma is-proportional-to epsilon(x) (epsilon=(T-T(c))/T(c)) in the regions -4 < In epsilon < -2. By choosing T(c) in different ways, it is shown that consistent results only could be obtained when T(c) is defined according to the Lawrence-Doniach theory.
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| 7. |
- Holm, William, et al.
(författare)
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Negative magnetoresistance in an yba2cu3O7-delta thin-film
- 1994
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194, s. 2309-2310
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Tidskriftsartikel (refereegranskat)abstract
- Negative magnetoresistance was observed in a thin YBa2Cu3O7-delta film which could be correlated with the presence of magnetic impurities. After empirical compensation for this effect the fluctuation conductivity was well described by the Aronov-Hikami-Larkin theory.
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| 8. |
- Holm, William, et al.
(författare)
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Study of magnetoresistance in oriented yba2cu3O7-delta thin-film
- 1994
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194, s. 2291-2292
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Tidskriftsartikel (refereegranskat)abstract
- The magnetoresistance of a c-axis oriented YBa2Cu3O7-delta thin film has been measured in magnetic fields, B, up to 12 T. The magnetic field was oriented both perpendicularly and parallel to the basal plane. The temperatures ranged up to epsilon = (T-T(c))/T(c) almost-equal-to 1/3 for B parallel-to c, while for B perpendicular-to the range was limited to epsilon less-than-or-equal-to 0.16. Analysis of the data in terms of superconducting fluctuations described by the Aronov-Hikami-Larkin theory is discussed.
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| 9. |
- Koptioug, Andrei, 1956-, et al.
(författare)
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Effect of External Magnetic Fields and Resonance Radio frequency Radiation on Radical Reactions
- 1990
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Ingår i: Physica. B, Condensed matter. - : Esevier. - 0921-4526 .- 1873-2135. ; 164:1-2, s. 200-204
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that an external magnetic field can affect the rate of singlet-triplet transitions in a radical pair and hence its recombination probability in liquid. Resonance radiofrequency (RF) radiation induces quantum beats in the kinetics of radical pair recombination. At high RF field amplitudes the singlet-triplet transitions in radical pairs can be efficiently suppressed.
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| 10. |
- Kubatkin, S E, et al.
(författare)
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Movement of scattering centers in a point contact induced by a scanning tunneling microscope
- 1994
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194-196:Part 1, s. 991-992
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Tidskriftsartikel (refereegranskat)abstract
- A new method is introduced to study transport in a mesoscopic sample. The electric field from an STM-tip is used to locally influence a mesoscopic object. We detect abrupt changes in the mesoscopic signal both as a function of the tip position and tip-sample voltage. They could be interpreted as due to spatial shifts or changes in the activity of scattering centers in the sample.
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| 11. |
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| 12. |
- Mattsson, J., et al.
(författare)
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Temperature dependence of free energy barriers in a Cu(7 at. % Mn) spin glass
- 1994
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 194-196:1, s. 305-306
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Tidskriftsartikel (refereegranskat)abstract
- Time dependent zero-field-cooled magnetisation measurements have been performed in order to determine the temperature dependence of the free energy barriers, B(T), in the spin glass Cu(7 at% Mn). The results have been analysed using the temperature dependence of the free energy barriers predicted in the droplet model, B( T)∝Δ( T) Lψ where L is the size of the droplet. It is found that as T→0 K, Δ (T)→constant, yielding activated dynamics in agreement with the droplet model. As T→ Tg, Δ (T) decreases but stays finite at Tg. This result is in contrast to the current droplet model where Δ (T)→0 when T→ Tg.
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| 13. |
- NISKANEN, K, et al.
(författare)
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ANTI-MEISSNER EFFECT AND LOW-FIELD MAGNETIC-RELAXATION IN SINTERED BI-2212
- 1994
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194, s. 1549-1550
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the low field magnetic properties of some sintered Bi-2212 samples has been performed. For sufficiently low applied magnetic fields, typically for fields H < 0.2 Oe, the field-cooled magnetisation becomes positive at some temperature below T(C) (anti-Meissner effect), contrary to the usual Meissner effect. The field dependence of this effect is comparable to the predicted behaviour for a system in an orbital glass state. Additionally, the relaxation of the zero-field-cooled magnetisation displays an unexpected field dependence, the relaxation rate S = partial-derivative M/partial-derivative log(t) increases as H(alpha) with alpha almost-equal-to 0.9 at very low fields. In contrast to the behaviour found in sintered YBCO, this result is not accounted for in conventional flux creep models, where the prediction is alpha greater-than-or-equal-to 2.
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