High<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>Superconductivity 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>by Nonadiabatic Pairing

Cappelluti, E.; Ciuchi, S.; Grimaldi, Claudio; Pietronero, L.; Strässler, S.

doi:10.1103/physrevlett.88.117003

Cited by 56 publications

(34 citation statements)

References 31 publications

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“…Nonadiabatic processes strongly affecting the occurrence of superconductivity have been put forward, by Alexandrov based on penetration depth data [17] and by Cappelluti et al on the basis of several experimental results that are not readily understandable in terms of conventional (isotropic) Eliashberg theory. [18] Although the crystal structure of MgB 2 is quite simple, it is strongly layered and electronic characteristics are predicted to be strongly anisotropic. So far few single crystals have been obtained, so single crystal optical conductivity data is not available.…”

Section: Introductionmentioning

confidence: 99%

Fermi surfaces of diborides: MgB2andZrB2

Rösner

Pickett

et al. 2002

Phys. Rev. B

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We provide a comparison of accurate full potential band calculations of the Fermi surfaces areas and masses of MgB2 and ZrB2 with the de Haas-van Alphen date of Yelland et al. and Tanaka et al. respectively. The discrepancies in areas in MgB2 can be removed by a shift of σ bands downward with respect to π bands by 0.24 eV. Comparison of effective masses lead to orbit averaged electron-phonon coupling constants λσ=1.3 (both orbits), λπ=0.5. The required band shifts, which we interpret as an exchange attraction for σ states beyond local density band theory, reduces the number of holes from 0.15 to 0.11 holes per cell. This makes the occurrence of superconductivity in MgB2 a somewhat closer call than previously recognized, and increases the likelihood that additional holes can lead to an increased Tc.

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Section: Introductionmentioning

confidence: 99%

Fermi surfaces of diborides: MgB2andZrB2

Rösner

Pickett

et al. 2002

Phys. Rev. B

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“…Together with the 2D structure of the corresponding sheet of the Fermi surface, this leads to a constant density of states at the Fermi energy and, correspondingly, to very large EPI with partial λ σ (the EPI parameter in the σ band) of about ∼ 25 [20]. Cappelluti et al [21] point out that the small Fermi velocity for charge carriers along the ΓA direction leads to a large nonadiabatic correction to T c (about twice as much compared with the adiabatic Migdal-Eliashberg treatment). Although this interaction is a driving force to high T c in this compound, it does not lead to crystal structure instability, since it occupies only a small volume in the phase space.…”

Section: Mechanism For High Tc In Mgb2mentioning

confidence: 99%

Advances in point-contact spectroscopy: two-band superconductor MgB2 (Review)

Yanson

Naǐdyuk

2004

Low Temperature Physics

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Analysis of the point-contact spectroscopy (PCS) data on the new dramatic high-Tc superconductor MgB2 reveals quite different behavior of two disconnected σ and π electronic bands, deriving from their anisotropy, different dimensionality, and electron-phonon interaction. PCS allows direct registration of both the superconducting gaps and electron-phonon-interaction spectral function of the two-dimensional σ and three-dimensional π band, establishing correlation between the gap value and intensity of the high-Tc driving force -the E2g boron vibration mode. PCS data on some nonsuperconducting transition-metal diborides are surveyed for comparison.

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“…տ [67], and a finite electron -phonon coupling (0) N l µ . This situation makes a finite electron-phonon coupling compatible with a low carrier density and small Fermi energy, suggesting the onset of nonadiabatic effects as far as F E becomes of the same order of the phonon frequencies ph w [39]. As a matter of fact, however, the comparison between the s band Fermi energy F 0 4 0 6 E s .…”

Section: Mgb 2 and Diboride Alloysmentioning

confidence: 92%

“…Polaron and bipolaron concepts [29][30][31][32], as well as anomalous features arising from lattice modulations (stripes) or instabilities [33,34], have been also employed to analyze phenomenology of the high-c T compounds. In the past years we have proposed that nonadiabatic effects could be responsible for the high-c T superconductivity in these compounds in the context of an unconventional phonon-based mechanism [35][36][37][38][39]. Nonadiabatic effects arise when the Fermi energy is small enough to be comparable with the phonon frequencies ph w : F p h ∼ E w [40].…”

Section: Introductionmentioning

confidence: 97%

Nonadiabatic electron–phonon effects in low carrier density superconductors

Cappelluti

Pietronero

2004

Physica Status Solidi (b)

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Different families of unconventional superconductors present a low charge carrier density as a common trait, suggesting that the low charge density can be at the basis of a unifying picture for different superconductors. In the past years we have suggested that the electron -phonon interaction can be responsible for a high-c T superconducting pairing in a nonadiabatic regime, where nonadiabatic effects are triggered on by the small electronic Fermi energy associated with the low charge density character. A coherent picture of such a framework requires however reconciling the low charge density and the small Fermi energy with a finite metallic character (sizable density of states and large Fermi surfaces). In this paper we investigate the peculiar conditions which are needed to be encountered in order to fulfill these requirements. We discuss the specific case of fullerenes, cuprates and MgB 2 alloys by analyzing their specific structural and electronic properties The comparison between these materials and simple instructive models permits to underline the different routes to reconcile these characteristics in different compounds. In cuprates and fullerenes the interplay between small Fermi energies and large Fermi surface is strictly connected with strong electronic correlation effects. A comprehensive understanding of these issues can be useful to the future search for new nonadiabatic high-c T materials.

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HighTcSuperconductivity inMgB2by Nonadiabatic Pairing

Cited by 56 publications

References 31 publications

Fermi surfaces of diborides: MgB2andZrB2

Fermi surfaces of diborides: MgB2andZrB2

Advances in point-contact spectroscopy: two-band superconductor MgB2 (Review)

Nonadiabatic electron–phonon effects in low carrier density superconductors

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