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46 results on '"Ahlheim, U."'

7. Evidence for bulk oxygen inLa2CuO4+δ: Specific-heat studies

Author

G. Fraunberger, Eugene L. Venturini, David S. Ginley, G. R. Stewart, Bruno Morosin, Bohdan Andraka, Jungsoo Kim, J. E. Schirber, and Ahlheim U

Subjects
Superconductivity, chemistry.chemical_classification, Materials science, High-temperature superconductivity, Specific heat, La2CuO4+delta, Analytical chemistry, chemistry.chemical_element, Thermodynamics, Oxygen, law.invention, chemistry, Electrical resistivity and conductivity, law, Inorganic compound, Stoichiometry
Abstract

Specific-heat measurements of a powder sample of La{sub 2}CuO{sub 4+{delta}} with {delta}{similar to}0.13 indicate the presence of bulk oxygen, as determined by transitions at 24, 43.7, and 54.5 K as found in solid O{sub 2}. A large difference in the cubic specific-heat temperature coefficients of a high-pressure-oxygenated superconducting sample and an ambient-pressure-oxygenated nonsuperconducting sample of La{sub 2}CuO{sub 4+{delta}} can be attributed to the unbound oxygen. Electronic specific-heat coefficients {gamma} of the two samples are 2.4{plus minus}0.3 and 0{plus minus}0.3 mJ/K{sup 2} mol, respectively. Effects of bulk oxygen on measured thermodynamic properties of high-temperature superconductors are discussed.

Published
1990
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13. Instabilities in heavy-fermion systems

Author

Steglich, F., primary, Ahlheim, U., additional, Bredl, C.D., additional, Geibel, C., additional, Grauel, A., additional, Lang, M., additional, Sparn, G., additional, Krimmell, A., additional, Loidl, A., additional, and Assmus, W., additional

Published
1992
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16. Phase transitions in the heavy Fermi-liquid state: CeCu2Si2, UNi2Al3 and UPd2Al3

Author

Steglich, F., primary, Ahlheim, U., additional, Böhm, A., additional, Bredl, C.D., additional, Caspary, R., additional, Geibel, C., additional, Grauel, A., additional, Helfrich, R., additional, Köhler, R., additional, Lang, M., additional, Mehner, A., additional, Modler, R., additional, Schank, C., additional, Wassilew, C., additional, Weber, G., additional, Assmus, W., additional, Sato, N., additional, and Komatsubara, T., additional

Published
1991
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17. Cooperative Effects in CeCu2Si2

Author

Lang, M, primary, Modler, R, additional, Ahlheim, U, additional, Helfrich, R, additional, Reinders, P H P, additional, Steglich, F, additional, Assmus, W, additional, Sun, W, additional, Bruls, G, additional, Weber, D, additional, and Lüthi, B, additional

Published
1991
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24. Magnetic behavior of Ce(Cu1−xAgx)6

Author

G. R. Stewart, Jung-Do Kim, G. Fraunberger, Bohdan Andraka, and Ahlheim U

Subjects
Diffraction, Materials science, Condensed matter physics, Band gap, Doping, X-ray crystallography, Electronic structure, Electronic band structure, Néel temperature, Magnetic susceptibility
Abstract

We have investigated doped CeCu{sub 6} via x-ray diffraction, dc and ac susceptibility, and specific heat in zero and applied magnetic field with a primary focus on the magnetic behavior caused by Ag doping. We present evidence from bulk specific heat and metallography data that the limit of Ag solubility in Ce(Cu{sub 1{minus}{ital x}}Ag{sub {ital x}}){sub 6} is {ital x}{similar to}0.1. Data below the magnetic ordering temperature may be fit to an exponential temperature dependence, implying a weak-coupled energy gap of {Delta}=0.58 K, contradicting an earlier report that {ital C} behaves linearly with temperature with a {gamma} over 3 J/mol K{sup 2} in the ordered state. Comparisons to magnetically ordered, doped UPt{sub 3} are made.

Published
1989
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25. Critical magnetic fields and specific heats of heavy fermion superconductors

Author

Rauchschwalbe, U., Ahlheim, U., Bredl, C.D., Mayer, H.M., and Steglich, F.

Abstract

The present status concerning lower and upper critical magnetic fields, Bc1(T) and Bc2(T), and specific heats, Cs(T), of heavy-fermion superconductors is reviewed. For CeCu2Si2, the data near Tcare found to be in full accord with GL theory. Yet, a surprising enhancement of the elastic mean free path over that in the normal state is inferred. Structure in both Bc1(T) and Bc2(T) of UBe13appears related to a bump in the normal-state specific heat (B= 0) around T= 0.5 This may be a precursor to the lower of the two calorimetric transitions inU0.97Th0.03Be13which are confirmed by new Bc1(T)… results.

Published
1987
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26. Superconductivity and magnetic order in a strongly interacting fermi-system: URu2Si2

Author

Schlabitz, W., Baumann, J., Pollit, B., Rauchschwalbe, U., Mayer, H. M., Ahlheim, U., and Bredl, C. D.

Abstract

Measurements are reported on the electrical resistivity, susceptibility, dc-Meissner effect and specific heat of the tetragonal U-compound URu2Si2. AtTN?17 K, an antiferromagnetic phase transition is observed. This magnetically ordered state appears to coexist with superconductivity, which is found belowTc?1.5 K. An analysis of the upper critical field data reveals rather, unusual properties of both the normal- and the superconducting state. The effective mass of the quasiparticles at low temperatures is substantially enhanced (m*?50 m0),though the measured low-temperature specific heat coefficient ? does not exceed 65 mJ/K2mol.

Published
1986
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27. Upper critical magnetic fields of the heavy fermion superconductors CeCu2Si2, UPt3, and UBe13: Comparison between experiment and theory

Author

Rauchschwalbe, U., Ahlheim, U., Steglich, F., Rainer, D., and Franse, J. J. M.

Abstract

We report measurements of the upper critical magnetic field,Bc2(T), on single crystal and polycrystalline samples of the heavy-fermion superconductors CeCu2Si2, UPt3 and UBe13. Comparison is made with experimental results for a “conventional” superconductor (CeRu3Si2) and with results of the weak-coupling theory applied to both ans-wave superconductor in the “dirty-limit” and ap-wave superconductor. New anomalies are discovered to add to the unusualBc2(T) behavior.

Published
1985
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36. Thermodynamic and transport properties of high-Tcsuperconductors

Author

Steglich, F, primary, Ahlheim, U, additional, Ewert, D, additional, Gottwick, U, additional, Held, R, additional, Kneissel, H, additional, Lang, M, additional, Rauchschwalbe, U, additional, Renker, B, additional, Rietschel, H, additional, Sparn, G, additional, and Spille, H, additional

Published
1988
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38. Heavy-fermion superconductivity atTc=2K in the antiferromagnet UPd2Al3

Author

Geibel, C., Schank, C., Thies, S., Kitazawa, H., Bredl, C. D., Böhm, A., Rau, M., Grauel, A., Caspary, R., Helfrich, R., Ahlheim, U., Weber, G., and Steglich, F.

Abstract

UPd2Al3 is a new heavy-fermion superconductor with a recordTc of 2 K. In addition, it shows a transition to long-range antiferromagnetic order atTN=14 K. Its Sommerfeld coefficient is reduced from ?p=210mJ/K2 mole in the paramagnetic to ?0=150mJ/K2 mole in the antiferromagnetic phase.

Published
1991
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