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Scaling of the critical temperature with the Fermi temperature in diborides (Articolo in rivista)

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Scaling of the critical temperature with the Fermi temperature in diborides (Articolo in rivista) (literal)

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Bianconi A., Agrestini S., Di Castro D., Campi G., Zangari G., Saini N.L., Saccone A., De Negri S., Giovannini M., Profeta G., Continenza A., Satta G., Massidda S., Cassetta A., Pifferi A., Colapietro M. (2002)
Scaling of the critical temperature with the Fermi temperature in diborides
in Physical review. B, Condensed matter and materials physics; APS, American physical society, College Park, MD (Stati Uniti d'America)
(literal)

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Bianconi A., Agrestini S., Di Castro D., Campi G., Zangari G., Saini N.L., Saccone A., De Negri S., Giovannini M., Profeta G., Continenza A., Satta G., Massidda S., Cassetta A., Pifferi A., Colapietro M. (literal)

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In this work we study the onset of the high-Tc phase going from AlB2 to MgB2 by a synthesis of solid solutions Al1-xMgxB2, with a variable Mg content, and the results are compared with a full band-structure calculation. The present results provide a solid experimental base for the understanding of the onset of the high-Tc phase coming from the low-Tc metallic phase induced by changing both the charge density and the microstrain of the boron sublattice. (literal)

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The recent discovery of a high-Tc phase in MgB2 and C60, intercalated with CHBr3, showed that the high-Tc phase occurs in metallic heterostructures at the atomic limit, where a superlattice is made of metallic units (boron layers or C60 buckyballs intercalated by a different material (Mg layers or CHBr3 molecules). The process for Tc amplification in these systems requires tuning the Fermi level at a \"shape resonance\" of the superlattice where the Fermi velocity in the direction of the superlattice modulation goes to zero and the Fermi surface topology shows a dimensional cross. MgB2 is a diboride where the Fermi level Ef is below the top of the s sub band of the boron superlattice at Ea. AlB2 is the prototype compound for this structure type, where conversely, the Fermi levei is at Ef>Ea as in most of diborides. (literal)

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1 INFM e Uni Roma 1. 2 Uni Genova. 3 INFM e Uni Aquila. 4 INFM Uni Cagliari. 5 CNR IC. 6 Uni Roma 1. (literal)

Titolo

Scaling of the critical temperature with the Fermi temperature in diborides (literal)

Abstract

The experimental determination of the scaling of the superconducting critical temperature (Tc) vs the Fermi temperature (Tf) of the holes in the boron s subband is presented. The Fermi level has been tuned near the \"shape resonance\" i.e., the two- to three-dimensional crossover of the Fermi surface of the boron s subband by changing the Al/Mg content in Al1-x Mgx B2. The product kfy0 of the Fermi wave vector (kf) times the superconducting Pippard coherence length (yo), that is a measure of the pairing strength, remains constant, kfy0=90 for x > 0.66. This high-Tc phase occurs in the boron superlattice under a tensile microstrain in the range 3%< e <6%. (literal)

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