A superconductor made by a metal heterostructure at the atomic limit tuned at the `shape resonance': MgB₂*

Abstract

We have studied the variation of superconducting critical temperature Tc as a function of charge density and lattice parameters in Mg1-xAlxB2 superconducting samples. The AB2 heterostucture of metallic boron layers (intercalated by A = magnesium, aluminum layers, playing the role of spacers) is made by direct chemical reaction. The spacing between boron layers and their charge density are controlled by chemical substitution of Mg by Al atoms. We show that high Tc superconductivity is realized by tuning the chemical potential at a `shape resonance' according with the patent for `high-temperature superconductors made by metal heterostructures at the atomic limit'. The energy width of the superconducting shape resonance is found to be about 400 meV.

Shape Resonance at a Lifshitz Transition for High Temperature Superconductivity in Multiband Superconductors

“…[15] Here we report additional support for the 1993 proposed paradigm [16] for understanding HTS, that allows the material design of new HTS, [17,18] based on the fact that:…”

Feshbach Shape Resonance in Multiband Superconductivity in Heterostructures

“…The increase of the critical temperature determined by the Feshbach shape resonance [125,162,180] of the interband pairing is given by ∆T c T F = (T c (exp) − T c (BCS)) T F that is plotted in Fig. 7 as a function of Lifshitz parameter z.…”

Anomalous Thermal Expansion in Superconducting Mg1− x Al x B2 System

“…In fact it is actually a composite intermetallic formed by a multilayer of first planes of a bulk low T c superconductor, boron that shows T c =11K under pressure [14]: graphene B monolayers, intercalated by second metallic planes of a non superconducting element, magnesium [14]: hcp Mg monolayers. Therefore following the discovery of Nagamatsu et al [13] it was first proposed by the Rome group [15][16][17] that MgB 2 shows mutigap superconductivity. The multigap superconductivity in MgB 2 was quickly confirmed by experiments on the upper critical field H c2 (T) [18], tunneling [19] and angular resolved photoemission (ARPES) [20] and many other measurements [2].…”