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  • 1
    Digitale Medien
    Digitale Medien
    Influence of neutron irradiation on the thermal conductivity of vapor-deposited diamond (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1515-1517 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The influence of neutron irradiation on the thermal conductivity κ of diamond films fabricated by hot filament (HF) and microwave plasma assisted (MPA) deposition has been studied. The additional thermal resistivity induced by irradiation is similar to that found in single crystal diamond and is due mainly to the formation of clusters of disordered carbon material. Despite a significant difference in κ prior to irradiation, the thermal conductivity of the HF and MPA films is almost the same after a cumulative dose of 2.7×1017 neutrons cm−2.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357727
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  • 2
    Digitale Medien
    Digitale Medien
    An alternate route to giant magnetoresistance in MBE-grown Co–Cu superlattices (invited) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6174-6177 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Co–Cu superlattices grown by MBE in the (111) orientation show weak or nonexistent interlayer exchange coupling, yet several groups have observed large high-field magnetoresistance signals in excess of 30%. In the present work, we address some of the questions relating to GMR and the interlayer coupling by studying samples with atomically abrupt interfaces, as probed by real-time RHEED techniques, HRTEM, and spin-echo NMR. We propose that the lowered dimensionality of the structure leads to an enhancement of the scattering of conduction electrons from paramagnetic interfaces obeying a Langevin-like saturation at very high fields, well beyond the switching field of the Co layers. Scaling between the GMR and thermopower measurements suggests that a spin-dependent density of states at the Co–Cu interfaces is responsible for the observed magnetotransport behavior in these samples, rather than antiferromagnetically coupled Co layers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.355447
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  • 3
    Digitale Medien
    Digitale Medien
    Thermoelectric properties of the n-type filled skutterudite Ba0.3Co4Sb12 doped with Ni (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 3698-3705 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Synthesis and electrical and thermal transport properties are reported for several filled skutterudite compounds doped with Ni: Ba0.3NixCo4−xSb12 with 0〈x〈0.2. Divalent Ba readily fills the cages of the skutterudite structure and is effective in reducing the thermal conductivity of the structure. The presence of a small amount of Ni increases the electron concentration, further reduces the thermal conductivity, and enhances the thermoelectric power factor. Hall mobility studies indicate that the addition of Ni to the system has the effect of increasing the relative strength of ionized impurity scattering as compared to acoustic phonon scattering. These results suggest that doping with Ni is an attractive avenue to optimization of filled skutterudites. The dimensionless thermoelectric figure of merit ZT was observed to increase from a value of 0.8 at 800 K for Ba0.3Co4Sb12 to a value of 1.2 for the sample with x=0.05. These materials show considerable potential as n-type legs in thermoelectric power generation at elevated temperatures. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1450036
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  • 4
    Digitale Medien
    Digitale Medien
    Pulsed terahertz-beam spectroscopy as a probe of the thermal and quantum response of YBa2Cu3O7−δ superfluid (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3022-3024 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Pulsed terahertz spectroscopy is used to determine the superfluid response of a YBa2Cu3O7−δ film under both thermal and optical stimulation. The coherent, time-domain technique is used in a novel configuration to directly measure the complex conductivity of the film versus temperature and continuous-wave laser illumination. At 0.6 Tc, the superfluid shows an identical response regardless of whether the stimulus is thermal or optical. This contrasts with the behavior of the superfluid at 0.26 Tc, where dramatic differences are observed depending on whether the sample is heated or subjected to optical illumination. It is suggested that these differences arise from an enhanced contribution due to quantum effects, and thus also from a strong temperature dependence of the quasiparticle recombination time at low temperatures. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.114939
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  • 5
    Digitale Medien
    Digitale Medien
    Use of high-Tc superconductors for the determination of absolute thermoelectric power (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4636-4638 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The use of the recently discovered high-Tc superconductors for purposes of precision determination of the absolute thermoelectric power is illustrated on commercially available wires of copper and Nb-Ti. High-Tc superconductors offer a wide range of temperatures where precision metrology can be carried out, and their unusually steep upper critical field allows for an accurate determination of the effect of magnetic field on the thermopower of test leads.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.339011
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  • 6
    Digitale Medien
    Digitale Medien
    Ultrafast nonequilibrium carrier relaxation in single-crystal Nd1.85Ce0.15CuO4−y (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 979-981 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a temperature-dependent investigation of the femtosecond relaxation dynamics of the n-type superconductor Nd1.85Ce0.15CuO4−y using ultrashort pulses from a Ti-sapphire laser in a transient absorption, pump-probe configuration. The energy relaxation time of the single crystals in the normal state was observed to increase by over an order of magnitude as the critical temperature was approached. This behavior has been modeled by the scattering of electrons with two-dimensional phonons. In the superconducting state, an increase and subsequent saturation of the relaxation time has been discerned. A possible reason for this is a complex interplay among the characteristic relaxation times, including scattering and recombination of quasiparticles optically excited by ultrashort laser pulses and order parameter relaxation close to Tc.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.109864
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  • 7
    Digitale Medien
    Digitale Medien
    Correlating optical absorption and thermal conductivity in diamond (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 165-167 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The presence of defects in diamond induces one-phonon infrared absorption which is not allowed in the perfect crystal due to symmetry. Concomitantly the thermal conductivity is reduced by additional phonon-defect scattering. For single crystal diamonds irradiated with fast neutrons, we find a correlation between the one-phonon absorption and the room-temperature thermal conductivity valid over three orders of magnitude in defect concentration. This relation holds for both unannealed and annealed crystals for which the detailed configuration of defects is different, as well as for a synthetic diamond film containing a similar type of disorder. Infrared absorption can thus be used to determine the thermal conductivity of diamonds containing vacancy-related defect centers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.110387
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  • 8
    Digitale Medien
    Digitale Medien
    Heat conduction in Ba1−xKxBiO3 (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 445-448 
    Details
    ISSN: 1572-9605
    Schlagwort(e): High-T c superconductors ; thermal conductivity ; magnetization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract We have investigated heat conduction of single crystal Ba1−xKxBiO3 in the temperature range of 2–300 K and in a magnetic field of up to 6 Tesla. Temperature dependence of thermal conductivityκ(T) reveals the participation of both electrons and phonons with their relative contributions that depend critically on the potassium doping concentration. Crystals underdoped with potassium (samples with higherT c) exhibit a strong suppression ofκ and a glass-like temperature dependence. In contrast, those with a higher potassium content (lowerT c) show an increase as temperature decreases with a peak near 23 K. Field dependence ofκ(H) is also very sensitive to the level of potassium doping. Crystals exhibiting a large phonon contribution show an initial drop inκ(H) at low fields followed by a minimum and then a slow rise to saturation as the field increases. The initial drop is due to the additional phonon scattering by magnetic vortices as the sample enters a mixed state. The high field behavior ofκ(H), arising from a continuous break-up of Cooper pairs, exhibits scaling which suggests the presence of an unconventional superconducting gap structure in this material.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00722826
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  • 9
    Digitale Medien
    Digitale Medien
    The peak in the thermal conductivity of Cu-O superconductors: Electronic or phononic origin? (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 323-329 
    Details
    ISSN: 1572-9605
    Schlagwort(e): High-T c superconductors ; thermal conductivity ; scattering rate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The thermal conductivityК of hole-doped Cu-O plane high-T c perovskites exhibits a dramatic increase belowT c which results in a pronounced peak nearT c /2. The origin of this peak was initially thought to arise from an enhancement in the mean-free path of phonons as the charge carriers undergo condensation. Indeed, excellent fits to the data can be obtained with physically reasonable parameters using the conventional theory of lattice conduction in superconductors. In contrast, a recently observed sharp decrease in the quasiparticle scattering rate of YBCO single crystals belowT c has motivated proposals for an electronic origin of the thermal conductivity peak. We shall critically examine experimental evidence and highlight relative advantages and shortcomings of the two contrasting interpretations. Furthermore, we shall draw attention to recently available data on the relaxation time of out-of-equilibrium carriers in Cu-O superconductors obtained using pump-probe femtosecond laser studies and what new light they shed on the controversy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00724562
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  • 10
    Digitale Medien
    Digitale Medien
    Thermal conductivity of high-T c superconductors (1990)
    Springer
    Journal of superconductivity 3 (1990), S. 337-389 
    Details
    ISSN: 1572-9605
    Schlagwort(e): High-Transition-temperature superconductors ; thermal conductivity ; single crystal ; Mechanisms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract This paper reviews existing data on the thermal conductivity of high-T c superconductors. Included are discussions of pristine polycrystalline high-T c ceramics, single crystal specimens, and high-T c materials structurally modified by substitution or by radiation damage. The thermal conductivity of high-T c superconductors is compared with that of conventional superconductors, and dramatic differences are found between the two families. Mechanisms of thermal conductivity applicable to high-T c perovskites are discussed and implications for theories of high-T c superconductivity are noted.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00617463
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