1. The amplification of the superconducting T c by combined effect of tuning of the Fermi level and the tensile micro-strain in Al 1 − x Mg x B 2
- Author
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Mauro Giovannini, Gianni Profeta, Paolo Postorino, Naurang L. Saini, D. Di Castro, Adriana Saccone, Gaetano Campi, S. De Negri, Sandro Massidda, A. Congeduti, Alessandra Continenza, M. Nardone, Marcello Colapietro, G. Satta, Augusto Pifferi, Stefano Agrestini, A. Cassetta, and Antonio Bianconi
- Subjects
Superconductivity ,Shape resonance ,Materials science ,Condensed matter physics ,Superlattice ,Fermi level ,General Physics and Astronomy ,chemistry.chemical_element ,Fermi surface ,Fermi energy ,Coherence length ,Condensed Matter::Materials Science ,symbols.namesake ,chemistry ,Condensed Matter::Superconductivity ,symbols ,Boron - Abstract
The increase of Tc with x in Al 1 − x Mg x B 2 is controlled by the Fermi level tuning at a "shape resonance" (i.e., the 2D-3D cross-over, at x = 0.66, of the topology of the Fermi surface of σ holes in the superlattice of boron mono-layers intercalated by Al 1 − x Mg x ions) and by the tensile "micro-strain" in the boron sub-lattice (due to the lattice misfit between the boron and the intercalated layers). The softening of the E2g phonon frequency with increasing boron tensile micro-strain e in the range 3% < e < 6% shows the increasing electron-lattice interaction. The linear scaling, for 0.66 < x < 1, of Tc vs. the Fermi temperature TF of the σ holes shows a constant coupling strength with kFξ0 = 90 (where kF is the Fermi wave vector and ξ0 is the Pippard coherence length) that points toward a vibronic pairing mechanism.
- Published
- 2002
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