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تسجيل مستخدم جديدRational Design of High-Tc Superconductivity in the Z = 6.0 Family
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O. Paul Isikaku-Ironkwe
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Rational design of superconductivity from Periodic Table properties is one of the grand challenges of superconductivity. We recently showed (Arxiv: 1208.0071) that high-Tc superconductivity exists in the Z = 5.667 with Ne=2.333. Here we propose and show that materials with Z = 6.0 and Ne =2.0 and 2.22 also meet the conditions for high-Tc superconductivity. We predict that the Ne=2.67 variety will not be superconducting but the ternary and quaternary systems of the Z =6.0 family with Ne=2.0 and 2.22 would have 12.5leqFw/Zleq25 and Tcs that fall in the range 60K - 100K. We provide material specific examples of such potential low-Z, Low-Ne high-Tc superconductors.
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The concepts of Rational Design of Superconductivity from Periodic Table properties were proposed in an earlier paper (ArXiv: 1204.0233). We had shown latter too that high-Tc superconductivity exists in the Z=7.333 family with Ne=2.667, of which MgB2
is a member. Here we propose and show that compounds with Z = 5.667 and Ne=2.333 will meet the conditions for high-Tc superconductivity similar to the Z = 7.333 family. The predicted Tcs for the ternary and quaternary systems of the Z =5.667 family would fall in the range 40K - 100K. We give material specific examples of some such possible rational designs of high-Tc superconductivity.
The superconducting transition temperatures of high-Tc compounds based on copper, iron, ruthenium and certain organic molecules are discovered to be dependent on bond lengths, ionic valences, and Coulomb coupling between electronic bands in adjacent,
spatially separated layers [1]. Optimal transition temperature, denoted as T_c0, is given by the universal expression $k_BT_c0 = e^2 Lambda / ellzeta$; $ell$ is the spacing between interacting charges within the layers, zeta is the distance between interacting layers and Lambda is a universal constant, equal to about twice the reduced electron Compton wavelength (suggesting that Compton scattering plays a role in pairing). Non-optimum compounds in which sample degradation is evident typically exhibit Tc < T_c0. For the 31+ optimum compounds tested, the theoretical and experimental T_c0 agree statistically to within +/- 1.4 K. The elemental high Tc building block comprises two adjacent and spatially separated charge layers; the factor e^2/zeta arises from Coulomb forces between them. The theoretical charge structure representing a room-temperature superconductor is also presented.
We report the occurrence of superconductivity, with maximum Tc = 40 K, in superlattices (SLs) based on two insulating oxides, namely CaCuO2 and SrTiO3. In these (CaCuO2)n/(SrTiO3)m SLs, the CuO2 planes belong only to CaCuO2 block, which is an antifer
romagnetic insulator. Superconductivity, confined within few unit cells at the CaCuO2/SrTiO3 interface, shows up only when the SLs are grown in a highly oxidizing atmosphere, because of extra oxygen ions entering at the interfaces. Evidence is reported that the hole doping of the CuO2 planes is obtained by charge transfer from the interface layers, which act as charge reservoir.
Introducing the generalized, non-extensive statistics proposed by Tsallis[1988], into the standard s-wave pairing BCS theory of superconductivity in 2D yields a reasonable description of many of the main properties of high temperature superconductors
, provided some allowance is made for non-phonon mediated interactions.
The layered lithium borocarbide LiBC, isovalent with and structurally similar to the superconductor MgB2, is an insulator due to the modulation within the hexagonal layers (BC vs. B2). We show that hole-doping of LiBC results in Fermi surfaces of B-C
p sigma character that couple very strongly to B-C bond stretching modes, precisely the features that lead to superconductivity at Tc = 40 K in MgB2. Comparison of Li{0.5}BC with MgB2 indicates the former to be a prime candidate for electron-phonon coupled superconductivity at substantially higher temperature than in MgB2.
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