| 1. |
- Bäckström, Joakim, et al.
(författare)
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Raman scattering in \RmYBa$_2$Cu$_4$O$_8$ and PrBa$_2$Cu$_4$O$_8$ : Indications of pseudogap effects in non-superconducting \RmPrBa$_2$Cu$_4$O$_8$
- 2000
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 61, s. 7049-7054
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Tidskriftsartikel (refereegranskat)abstract
- By analysis of the Raman spectra of superconducting YBa2Cu4O8 (Y-124), we observe a suppression of low-energy electronic density of states that we link to changes in the linewidth of the Ba-phonon mode. These effects occur at a temperature below 150 K, where also anomalies in resistivity and other physical properties take place. We argue that these changes in the Raman spectra of Y-124 are connected to the opening of a pseudogap. Analogous anomalies in resistivity and the Ba-phonon width in the nonsuperconducting homologue PrBa2Cu4O8 (Pr-124) below 150 K suggest that similar pseudogap effects can occur without a following transition to a superconducting state at a lower temperature.
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| 2. |
- Bäckström, Joakim, et al.
(författare)
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Raman scattering in YBa2Cu4O8 and PrBa2Cu4O8 - indications of pseudogap effects in non-superconducting PrBa2Cu4O8
- 2000
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 2251-2252
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Tidskriftsartikel (refereegranskat)abstract
- By analysis of the temperature evolution of Raman spectra, we connect an observed supression in low-energy electronic density of states to an anomalous sharpening of the Ba-phonon mode in superconducting YBa2Cu4O8 (Y-124) at around T=150 K. We link the supression of electronic excitations to an opening of a pseudogap. Similar effects observed for the Ba-phonon mode at roughly the same temperature in non-superconducting PrBa2Cu4O8 (Pr-124) suggests that a pseduogap opens up around 150 K also in this material.
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| 3. |
- Kall, M., et al.
(författare)
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Resonance Raman scattering as a probe of oxygen dynamics in YBa2Cu3Ox
- 1998
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Ingår i: Journal of Physics and Chemistry of Solids. - 0022-3697 .- 1879-2553. ; 59, s. 1988-1990
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Tidskriftsartikel (refereegranskat)abstract
- We report on the metastable photo-bleaching of the 2.15 eV yellow Raman resonance in oxygen deficient YBa2Cu3Ox (x = 6.35-6.87), extending investigations by Wake ct al. (Phys. Rev. Lett., 1991,67, 3728) for x approximate to 7. Polarization, x dependence and phonon spectra indicate that the resonance is localized at oxygen vacancies in long CuO-chains. The resonance is thermally reactivated from the metastable bleached state with a relaxation time tau similar to exp[Delta/k(B)T] with Delta approximate to 1 eV. The resulting temperature dependent equilibrium resonance intensity essentially miners the oxygen superstructure disordering around T* approximate to 100 degrees C observed in the same crystals by hard X-ray diffraction, thus offering a new effective probe of chain-oxygen dynamics in YBa2Cu3Ox. (C) 1998 Elsevier Science Ltd. All rights reserved.
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| 4. |
- Osada, M., et al.
(författare)
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In situ resonant Raman scattering and reversible photoinduced structural change in YBa2Cu3O6+x
- 2005
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 71
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Tidskriftsartikel (refereegranskat)abstract
- We report on bidirectional photoswitching associated with the CuO chains in oxygen-deficient YBa2Cu3O6+x single crystals. By varying the wavelength of light polarized along the CuO chains, the material can be reversibly switched between two metastable states characterized by the existence or absence of a specific Raman scattering resonance. A comparison of the spectral efficiencies for this photoswitching with analogous data for the persistent photoconductivity and photoconductivity quenching effects suggests that the two phenomena have the same microscopic origin. We argue that the effects are due to photoinduced Cu-O charge-transfer excitations, which destabilize chains of different length depending on wavelength, and promote the growth of thermally inaccessible oxygen ordering configurations.
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| 5. |
- Osada, M., et al.
(författare)
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Photoinduced effects and oxygen dynamics in YBa2Cu3Ox
- 2001
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 364, s. 545-548
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen-deficient YBa2Cu3Ox (Y123) exhibits persistent photoconductivity when illuminated by visible light. We have investigated resonant Raman spectra as a function of excitation wavelength and temperature, which shed new light on photoinduced effects and chain oxygen dynamics in Y123. Experimental evidence suggests that the mechanism behind the unusual photoinduced effects primary involves photoinduced oxygen ordering. Our Raman data also constitute the non-diffraction observations of the superstructure phase transition in Y123. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 6. |
- Osada, M., et al.
(författare)
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Resonant Raman scattering and photoinduced metastability in oxygen-deficient YBa2Cu3Ox
- 2000
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Ingår i: Physica C. ; 338, s. 157-160
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Tidskriftsartikel (refereegranskat)abstract
- We studied the photoinduced metastable states in oxygen-deficient YBa2Cu3Ox (Y123) (x = 6.35-6.87). The states are identified by the intensity dependences of CuO-chain resonance on photo irradiation and temperature. Below room temperature (RT) the CuO-chain resonance can be completely suppressed by irradiation with visible light polarized along the CuO chains, indicating photo-assisted oxygen ordering. Above RT, the resonance intensity returns and saturates at T > 100 degrees C. This behavior exactly reflects the temperature dependence of chain oxygen ordering in the same crystals observed by hard X-ray diffraction. The stability of the photo-induced state is in agreement with reported persistent photo-induced superconductivity effects. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 7. |
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| 8. |
- Kakihana, M., et al.
(författare)
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A simple and reproducible way to synthesize PrBa2Cu4O8 under 1 atm of oxygen by amorphous citrate method
- 1999
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 321, s. 74-80
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Tidskriftsartikel (refereegranskat)abstract
- A simple aqueous solution technique utilizing citric acid (CA) as a complexant was applied to prepare PrBa2Cu4O8 (Pr124) at ambient oxygen pressure. Heating of a mixed-solution of CA, water (H2O) and ions of Pr, Ba and Cu with a molar ratio of [CA]:[H2O]:[Pr + Ba + Cu] = 3.6:40:1 on a hot-plate set at 200 degrees C produced a transparent amorphous citrate "gel" without any precipitation, which after heat-treatment at 450 degrees C was converted to a precursor for Pr124. The Pr124 compound with only minor traces of BaCuO2, PrBaO3 and CuO formed after heat-treating the precursor twice at 850 degrees C for 60 h under 1 atm oxygen pressure. The amount of impurities in the citrate-derived Pr124 was approximately half of that in the best sample previously prepared by the more elaborate high-pressure technique. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 10. |
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