Phonon Density of States in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>MgB</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Osborn, R.; Goremychkin, E. A.; Kolesnikov, A. I.; Hinks, D. G.

doi:10.1103/physrevlett.87.017005

Cited by 204 publications

(158 citation statements)

References 14 publications

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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: 79%

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: 79%

Carbon solubility and superconductivity in MgB2

Bharathi

Balaselvi

Kalavathi

et al. 2002

Physica C: Superconductivity

119

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“…Replacing 10 B with 11 B results in a sizeable isotope shift [3] to lower temperatures which points to BCS superconductivity. Other experiments, such as heat capacity [4,5], photoemission spectroscopy [6], and inelastic neutron scattering [7,8] also support the picture that MgB 2 is a phonon-mediated superconductor in the weak-to-moderate coupling regime.High pressure studies traditionally play an important role in superconductivity. A large magnitude of the pressure derivative dT c /dP is a good indication that higher values of T c may be obtained through chemical means.…”

mentioning

confidence: 73%

“…We now repeat the same calculation with the McMillan equation for MgB 2 using the logarithmically averaged phonon energy from inelastic neutron studies [7] [33]. Inserting these values into Eq.…”

mentioning

confidence: 99%

Dependence ofTcon hydrostatic pressure in superconductingMgB2

et al. 2001

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The dependence of T c on hydrostatic (He-gas) pressure for superconducting MgB 2 has been determined to 0.7 GPa. We find that T c decreases linearly and reversibly under pressure at the rate dT c /dP ≃ −1.11 ± 0.02 K/GPa. These studies were carried out on the same sample used in earlier structural studies under He-gas pressure which yielded the bulk modulus B = 147.2 ± 0.7 GPa. The value of the logarithmic volume derivative of T c is thus accurately determined, d ln T c /d ln V = +4.16 ± 0.08, allowing quantitative comparison with theory. The present results support the emerging picture that MgB 2 is a BCS superconductor with electron-phonon pairing interaction. 1The recent discovery [1] of superconductivity in MgB 2 at T c ≃ 39 K has sparked worldwide a torrent of experimental and theoretical activity, reminiscent of the frenzy following the observation [2] of superconductivity in La-Ba-Cu-O at a comparable temperature almost 15 years ago. Replacing 10 B with 11 B results in a sizeable isotope shift [3] to lower temperatures which points to BCS superconductivity. Other experiments, such as heat capacity [4,5], photoemission spectroscopy [6], and inelastic neutron scattering [7,8] also support the picture that MgB 2 is a phonon-mediated superconductor in the weak-to-moderate coupling regime.High pressure studies traditionally play an important role in superconductivity. A large magnitude of the pressure derivative dT c /dP is a good indication that higher values of T c may be obtained through chemical means. It is not widely appreciated, however, that the pressure dependence T c (P ), like the isotope effect, contains valuable information on the superconducting mechanism itself. For example, in simple-metal BCS superconductors, like Al, In, Sn, and Pb, T c invariably decreases under pressure due to the reduced electron-phonon coupling from lattice stiffening [9]. More generally, an accurate determination of the dependence of both T c and the lattice parameters on pressure yields the functional dependence T c = T c [a(P ), b(P ), c(P )] which provides a critical test of theoretical models. Hirsch [10] and Hirsch and Marsiglio [11] have applied a theory of hole superconductivity to MgB 2 and predicted that for an optimally doped sample T c should increase with pressure, in contrast to the expected decrease in T c from lattice stiffening.Precise structural data on MgB 2 at room temperature (RT) have recently been obtained by Jorgensen et al.[12] for hydrostatic pressures to 0.6 GPa in a He-gas neutron diffraction facility which yield the anisotropic compressibilities d ln a/dP = −1.87 × 10 −3 GPa −1 , d ln b/dP = −3.07 × 10 −3 GPa −1 , and the bulk modulus B = 147.2 ± 0.7 GPa; the compressibility along the c axis is thus significantly (64%) larger than that along the a axis. The binding within the boron layers is evidently much stronger than between the layers. These results are in reasonable agreement with electronic structure calculations by Loa and Syassen [13].Recent synchrotron x-ray diffraction studi...

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“…The observation of a boron isotope effect has lead to MgB 2 being described as a phonon-mediated BCS superconductor [4] although the observed T c is at, or above, the early theoretical predictions based on phonon-mediated coupling within the BCS theory [6]. It has recently been shown that the T c can be as large as that observed within the moderate to strong phonon-mediated BCS theory due to the large density of states at the Fermi level and high phonon frequencies [7][8][9]. However, it has been suggested that the predicted crossing of the Fermi surface by the boron σ and π bands at different regions of the Brillouin zone can have a significant impact on superconductivity in MgB 2 [10,11].…”

Section: Introductionmentioning

confidence: 99%

Magnetization and microwave study of superconductingMgB2

et al. 2002

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We report magnetic field dependent magnetization and microwave impedance measurements on a MgB 2 superconductor prepared by high pressure synthesis. We find that the upper critical field is linearly dependent on temperature near T c and the dc irreversibility field exponent is ~1.4. The microwave data display an excess surface resistance below T c which is neither observed in low T c nor in high temperature superconductors (HTSC). The real part of the complex conductivity, σ 1 , shows a huge maximum below T c and the imaginary part, σ 2 , is linear for temperatures less than 20 K, which can not be simply accounted for by the weak coupling BCS model with an s-wave superconducting order parameter. We speculate that this may be due to the two gaps reported by other studies.Unlike measurements on the high temperature superconducting cuprates, we find no evidence of weak-links in the superconducting state. By inverting the magnetic field dependent impedance data, we find a vortex depinning frequency that decreases with increasing magnetic field and evidence for an anisotropic upper critical magnetic field.

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Phonon Density of States inMgB2

Cited by 204 publications

References 14 publications

Carbon solubility and superconductivity in MgB2

Carbon solubility and superconductivity in MgB2

Dependence ofTcon hydrostatic pressure in superconductingMgB2

Magnetization and microwave study of superconductingMgB2

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