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Putti, M.; d’Agliano, E. Galleani; Marrè, D.; Napoli, F.; Tassisto, M.; Manfrinetti, P.; Palenzona, A.; Rizzuto, C.; Massidda, S.

doi:10.1007/s10051-002-8934-z

Cited by 27 publications

(50 citation statements)

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“…λ is seen to increase correspondingly from 0.8 to 0.9. The extracted values of λ and θ D for pristine MgB 2 are in agreement with earlier estimates of these quantities from the specific heat experiments 26 , similar resistivity measurements 27 , phonon DOS measurements 28 and calculations 29 . DISCUSSION It can be seen from Fig.4, that the T c decreases with carbon fraction upto x=0.3, beyond which it shows no significant change.…”

Section: Methodssupporting

confidence: 89%

Carbon solubility and superconductivity in MgB2

Bharathi

Balaselvi

Kalavathi

et al. 2002

Physica C: Superconductivity

119

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Successful replacement of B by C in the series MgB 2-x C x for values of x upto 0.3 are reported. Resistivity and ac susceptibility measurements have been carried out in the samples. Solubility of carbon, inferred from the observed change in the lattice parameter with carbon content indicates that carbon substitutes upto x=0.30 into the MgB 2 lattice. The superconducting transition temperature, T C measured both by zero resistivity and the onset of the diamagnetic signal shows a systematic decrease with increase in carbon content upto x=0.30, beyond which the volume fraction decreases drastically. The temperature dependence of resistivity in the normal state fits to the Bloch-Gruneisen formula for all the carbon compositions studied. The Debye temperatures, θ D , extracted from the fit is seen to decrease with carbon content from 900K to 525K, whereas the electron-phonon interaction parameter, λ, obtained from the McMillan equation using the measured T C and θ D , is seen to increase monotonically from 0.8 in MgB 2 to 0.9 in the x=0.50 sample. The ratio of the resistivities between 300K and 40K versus T C is seen to follow the Testardi correlation for the C substituted samples. The decrease in T C is argued to mainly arise due to large decrease in θ D with C concentration and a decrease in the hole density of states at N(E F ).

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Section: Methodssupporting

confidence: 89%

Carbon solubility and superconductivity in MgB2

Bharathi

Balaselvi

Kalavathi

et al. 2002

Physica C: Superconductivity

119

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“…The κ(T ) values are about an order of magnitude higher than previously reported for polycrystalline samples. 23,24,25,26 Also the overall temperature dependence of κ is quite different from those earlier data. Instead of a monotonous increase with temperature we note a distinct maximum of κ(T ) at T ∼ 65 K. The cause of these differences is obviously the strong influence of intergrain boundaries on the heat transport in polycrystals, which masks the intrinsic mechanisms of quasiparticle scattering.…”

Section: A Electrical Resistivitycontrasting

confidence: 92%

“…23,24,25,26 This observation is quite unusual for superconductors with nonnegligible phonon heat transport, because the opening of the superconducting gap rapidly reduces the rate of phonon scattering on electrons and should lead to a fast increase of κ ph below T c . The assumptions that either the phonon-electron scattering is much weaker than phonondefect scattering, or that κ ph is negligibly small in the vicinity of T c , which, in principle, might explain the absence of a κ(T ) feature at T c , are all incompatible with the observation that applying a relatively weak external magnetic field of 0.63 kOe, introducing some additional quasiparticles in the cores of vortices, considerably reduces the thermal conductivity at intermediate temperatures (see Fig.…”

Section: A Thermal Conductivity In the Normal Statementioning

confidence: 99%

Thermal conductivity of single-crystallineMgB2

et al. 2002

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The ab-plane thermal conductivity κ of single-crystalline hexagonal MgB2 has been measured as a function of magnetic field H with orientations both parallel and perpendicular to the c-axis and at temperatures between 0.5 and 300 K. In the mixed state, κ(H) measured at constant temperatures reveals features that are not typical for common type-II superconductors. The observed behavior may be associated with the field-induced reduction of two superconducting energy gaps, significantly different in magnitude. A nonlinear temperature dependence of the electronic thermal conductivity is observed in the field-induced normal state at low temperatures. This behavior is at variance with the law of Wiedemann and Franz, and suggests an unexpected instability of the electronic subsystem in the normal state at T ≈ 1 K.

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“…We remind that magnetoresistance follows the Kohler law [2,3], resistivity follows the Bloch-Grüneisen relationship [4,5], Seebeck effect follows the Mott law [4] [6]. A further analysis is evidencing the important role in the transport properties of the peculiar band structure of this compound.…”

Section: Introductionmentioning

confidence: 93%

Two-band effects in the transport properties of MgB₂

Putti

Braccini

Galleani

et al. 2002

Supercond. Sci. Technol.

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We present resistivity and thermal conductivity measurements on bulk samples, prepared either by a standard method or by a one-step technique. The latter samples, due to their high density and purity, show residual resistivity values as low as 0.5 µΩ cm and thermal conductivity values as high as 215 W/mK, higher than the single crystal ones. Thermal and electrical data of all the samples are analysed in the framework of the Bloch-Gruneisen equation giving reliable parameter values. In particular the temperature resitivity coefficient, obtained both from resistivity and thermal conductivity, in the dirty sample comes out ten time larger than in the clean ones. This result supports the hypothesis of ref.[1] that π and σ bands conduct in parallel, prevailing π conduction in clean samples and σ conduction in dirty samples . IntroductionSince the discovery of superconductivity in Magnesium diboride, this compound appeared to be a "simple" metal where most of the electronic properties follow in a first approximation the basic transport laws of a metal where electron-phonon interaction is dominant. We remind that magnetoresistance follows the Kohler law [2,3], resistivity follows the Bloch-Grüneisen relationship [4,5], Seebeck effect follows the Mott law [4] [6]. A further analysis is evidencing the important role in the transport properties of the peculiar band structure of this compound. Two kinds of bands having quite different character contribute to the transport [7,8]: two σ bands, which are hole-type and two-dimensional (2D), and two π bands, which are electron-type and threedimensional (3D). Calculations showed that σ bands are more strongly coupled with phonon modes and in particular with the E 2g mode. A recent paper [1] suggests that just due to the different parity of the two bands, interband impurity scattering turns out to be negligible and the σ and π bands behave as two separate conduction channels in parallel. In this paper we discuss some implications that this fact does have on transport properties, namely electrical and thermal conductivity.

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Cited by 27 publications

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Carbon solubility and superconductivity in MgB2

Carbon solubility and superconductivity in MgB2

Thermal conductivity of single-crystallineMgB2

Two-band effects in the transport properties of MgB₂

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Untitled

Cited by 27 publications

References 0 publications

Carbon solubility and superconductivity in MgB2

Carbon solubility and superconductivity in MgB2

Thermal conductivity of single-crystallineMgB2

Two-band effects in the transport properties of MgB2

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Two-band effects in the transport properties of MgB₂