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Author (up) Castello, D.; Jaime, M.; Núñez Regueiro, M.
Title Thermal conductivity of high temperature superconductor TlBaCaCuO Type Journal Article
Year 1991 Publication Solid State Communications Abbreviated Journal Solid State Commun.
Volume 79 Issue 11 Pages 967-970
Keywords
Abstract We have measured the thermal conductivity of ceramic samples of TlBaCaCuO between 2 and 250 K. At high temperatures it follows a constant behaviour down to the superconducting transition temperature where a sudden increase of the thermal conductivity occurs, attributed to reduced phonon scattering by condensating electrons. At low temperatures a T2 law is observed, confirming the assumption that it is a common feature in most of the high temperature superconducting oxides. Phonon scattering against tunneling systems analogous to those found in amorphous solids can explain this behaviour.
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ISSN 0038-1098 ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number BT @ pedrazp @ Serial 581
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Author (up) Núñez Regueiro, M.; Castello, D.; Izbizky, M.A.; Esparza, D.; D'Ovidio, C.
Title Anomalous thermal conductivity of La2-xSrxCuO4: Possibility of a polaronic glass Type Journal Article
Year 1987 Publication Physical Review B Abbreviated Journal Phys. Rev. B
Volume 36 Issue 16 Pages 8813-8815
Keywords
Abstract e present measurements of the thermal conductivity of La2CuO4 and La1.85Sr0.15CuO4. The results on the pure sample show that lattice conduction is predominant with a T1.8 dependence at low temperatures and a strong T-independent scattering above 30 K. We observe a similar behavior for the superconductor but with a T1.4 law at low temperature and a small electronic contribution in the normal state. These results together with the behavior of the specific heat and sound attenuation are consistent with the existence of a two-level tunneling system for an amorphous state.
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Publisher American Physical Society Place of Publication Editor
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Notes Approved no
Call Number BT @ pedrazp @ 10.1103/PhysRevB.36.8813 Serial 574
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Author (up) Núñez Regueiro, M.; Esquinazi, P.; Izbizky, M.A.; Durán, C.; Castello, D.; Luzuriaga, J.
Title Tunneling systems in high temperature superconductors Type Journal Article
Year 1988 Publication Annales de Physique Abbreviated Journal Ann. Phys. Fr.
Volume 13 Issue 5 Pages 401-406
Keywords acoustic wave absorption; acoustic wave velocity; barium compounds; high temperature superconductors; lanthanum compounds; rare earth compounds; strontium compounds; superconductive tunnelling; thermal conductivity of solids; tunnelling systems; high temperature superconductors; thermal conductivity; sound attenuation; sound velocity; model; low temperature specific heat; La Sr Cu O
Abstract We have measured the thermal conductivity, sound attenuation and relative variation of sound velocity of compounds of the La-Sr-Cu-O and RBa2Cu3O7 families, where R is a rare-earth. We have found that all these properties can be quantitatively correlated within a tunneling system model similar to that used in amorphous materials. This interpretation would naturally explain the anomalous linear term of the low temperature specific heat observed in these materials.
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ISSN 0003-4169 ISBN Medium
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Notes ISI:A1988Q715000009 Approved no
Call Number BT @ hernan @ Serial 264
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Author (up) Núñez Regueiro, M.; Esquinazi, P.; Izbizky, M.A.; Duran, C.; Castello, D.; Luzuriaga, J.; Nieva, G.
Title Evidence of tunneling systems through thermal and acoustic measurements in ceramic materials Type Journal Article
Year 1988 Publication Physica C: Superconductivity and its applications Abbreviated Journal Physica C
Volume 153-155 Issue PART 2 Pages 1016-1017
Keywords Acoustic Variables Measurement--Wave Velocity; Ceramic Materials--Thermal Conductivity; Europium Barium Copper Oxides; Superconducting Materials
Abstract We have neasured the sound velocity, internal friction, thermal conductivity and specific heat of La-based and (Y/Eu)- based ceramics. The low temperature data can be understood in terms of the Tunneling Model assuming the existence of Tunneling Systems (TS). From these measured properties we obtain values for the parameter C=P?2/?v2, where P is the density of states of TS, ? the coupling constant between phonons and TS, ? the mass density and v the sound velocity close to those obtained for amorphous and “orientational” disordered crystalline materials. Our data would indicate that the TS are intrinsic defects independent of the sample porosity.
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Series Editor Series Title Abbreviated Series Title
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ISSN 09214534 (ISSN) ISBN Medium
Area Expedition Conference International Conference on High Temperature Superconductors and Materials and Mechanisms of Superconductivity
Notes Export Date: 28 April 2009; Source: Scopus; CODEN: PHYCE; Language of Original Document: English; Correspondence Address: Regueiro, M.N.; Centro At Approved no
Call Number BT @ luzuriag @ Serial 496
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Author (up) Núñez Regueiro, M; Castello, D.; Jaime, M.
Title Thermal conductivity of high temperature superconductors Type Journal Article
Year 1991 Publication Physica B: Condensed Matter Abbreviated Journal Physica B
Volume 169 Issue 1-4 Pages 631-632
Keywords
Abstract We have measured the thermal conductivity of Tl1Ba2Cu3O9 and of the related compounds CuO and La2CuO4. For the superconducting sample we observe the characteristic T2 behaviour at low temperatures, that does not appear in the non-superconducting samples. The superconducting transition and the antiferromagnetic ordering are detected by our measurements.
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Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0921-4526 ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number BT @ pedrazp @ Serial 582
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Author (up) Núñez Regueiro, M.; Mignot, J.-M.; Castello, D.
Title Superconductivity at High Pressure in NbSe3 Type Journal Article
Year 1992 Publication Europhysics Letters Abbreviated Journal Europhys. Lett.
Volume 18 Issue 1 Pages 53-57
Keywords
Abstract We have measured the electrical resistivity of NbSe3 between 2 K and room temperature up to a pressure of 7.2 GPa. At P1 = 3.5 GPa we observe the extinction of the high-temperature charge density wave (T1-CDW) and the enhancement of the superconducting critical temperature Tc to [?] 5 K. The logarithmic pressure slopes of T1 (P < P1) and Tc (P > P1) are found to be practically equal. A similar behaviour had been reported previously at lower pressures for T2 (P < P2) and Tc (P2 < P < P1) in the distorted state. We discuss these results in terms of an anisotropic superconducting state in NbSe3, with different gaps associated with different types of chains.
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Publisher Place of Publication Editor
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Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0295-5075 ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number BT @ pedrazp @ 0295-5075-18-1-010 Serial 578
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Author (up) Núñez Regueiro, M.; Castello, D.
Title Thermal conductivity of high temperature superconductors Type Journal Article
Year 1991 Publication International Journal of Modern Physics B Abbreviated Journal Int. J. Mod. Phys. B
Volume 5 Issue 12 Pages 2003-2035
Keywords
Abstract We review and analyze the data on the thermal conductivity of both ceramic and single crystal samples of high temperature superconductors. A universal pattern can be extracted and interpreted in the following way: phonons are the main heat carriers in these materials, and in the high temperature range the thermal conductivity κ is almost constant due to phonon scattering against disorder; below the superconducting transition temperature κ increases as phonon scattering against carriers condensing into the superconducting state decreases and at still lower temperatures there is a region in which a T2 law is obeyed that most probably is due to resonant phonon scattering against low energy excitations, i.e. tunneling systems similar to those found in disordered materials. The origin of the relevant disorder is discussed.
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Notes Approved no
Call Number BT @ pedrazp @ Serial 584
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Author (up) Núñez Regueiro, M.; Mignot, J.M.; Jaime, M.; Castello, D.; Monceau, P.
Title Superconductivity under pressure in linear chalcogenides Type Journal Article
Year 1993 Publication Synthetic Metals Abbreviated Journal Synth. Met.
Volume 56 Issue 2-3 Pages 2653-2659
Keywords
Abstract We have measured the electrical resistivity of several quasi 1-D chalcogenides between 1.2 and 300K and from ambient pressure up to 25GPa. On NbSe3 we find that the high temperature charge density wave (CDW) transition T1 disappears at a pressure of about 3.5GPa, where the superconducting transition temperature Tc jumps to not, vert, similar5K. The similar pressure dependence of the logarithmic pressure derivative of both T1 and Tc above this pressure suggests the existence of independent superconducting states. On m-TaS3 we observe a maximum on the T1-P variation at not, vert, similar3.5GPa, that we attribute to a CDW transition temperature strongly diminished by 1-D fluctuations that are reduced at low applied pressures, with T2 behaving in a monotonous decreasing way with pressure. While on o-TaS3 the CDW that develops at 210K at ambient pressure, gives way to a superconducting state of Tcnot, vert, similar3K at a pressure of 6.5GPa. The behaviour of (TaSe4)2I is scaled to the precedent, with a higher critical pressure of 15GPa that induces the appearance of a superconducting state with Tc=2.5K.
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ISSN 0379-6779 ISBN Medium
Area Expedition Conference International Conference on Science and Technology of Synthetic Metals
Notes Approved no
Call Number BT @ pedrazp @ Serial 579
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