The loss of anisotropy in MgB₂with Sc substitution and its relation with the critical temperature

Abstract

The electrical conductivity anisotropy of the σ-bands is calculated for the (Mg,Sc)B 2 system using a virtual crystal model. Our results reveal that anisotropy drops with relatively little scandium content (< 30%); this behaviour coincides with the lowering of T c and the reduction of the Kohn anomaly. This anisotropy loss is also found in the Al and C doped systems. In this work it is argued that the anisotropy, or 2D-character, of the σ-bands is an important parameter for the understanding of the high T c found in MgB 2 .

Neutron Irradiation of Sm-1111

“…This decrease is ascribed to d-wave superconductivity in the cuprates 30,31 , the reason for the reduction in T c of SmFeAsO 1−x F x is currently unknown. A moderate amount of non-magnetic impurities does not reduce T c in isotropic single band superconductors, thus the anisotropy 32,33,34 or multiband superconductivity 35,36,37,38 are possible candidates for explaining this decrease. Recently, a suppression of T c by impurity scattering was also predicted for extended s-wave superconductors 39 .…”

Theoretical Study of Screening Dependence of Aluminium Doped MgB 2

“…The superconductivity in MgB 2 is mainly due to the 𝜎 bands. [31] MgB 2 samples can be understood mainly in terms of a band filling effect due to the electron doping by Al. Mora et al [32] found that the Al extra electron starts to fill up the 𝜎 bands, and at 56% of Al replacement these bands become saturated and the system is no longer superconducting, [31] thus SSP 𝜆 and 𝑇 c decrease with the rising doping level of Al in the Mg 1−𝑥 Al 𝑥 B 2 system.…”

“…[31] MgB 2 samples can be understood mainly in terms of a band filling effect due to the electron doping by Al. Mora et al [32] found that the Al extra electron starts to fill up the 𝜎 bands, and at 56% of Al replacement these bands become saturated and the system is no longer superconducting, [31] thus SSP 𝜆 and 𝑇 c decrease with the rising doping level of Al in the Mg 1−𝑥 Al 𝑥 B 2 system. [33,34] The values of Coulomb pseudopotential 𝜇 * , which accounts for the Coulomb interaction between the conduction electrons, obtained from five different forms of dielectric screening are tabulated in Table 1.…”

“…This predicts that 𝑇 c in the present work is very close to 𝑇 c = 3 K according to many experimental and theoretical results. [33,44] As a result, the inter-band scattering increases and additionally, DOS in the hole 𝜎 band decreases. Transmission electron microscopy (TEM) [11] also shows that the aluminium substitution leads to the formation of superstructure MgAlB 4 which inter grows with MgB 2 that leads to the suppression of superconductivity.…”

Effects on transition temperature and Raman spectra of substitution of Cr and Al for Mg in MgB2

“…These changes of crystal structure induced by Mg site doping will give an effective influence on the electronic nature of this system. By the electronic structure calculations, Ruiz-Chavarria et al [45] have reported that the electronic structure of ScB 2 is quite different to AlB 2 . Even with a small Sc substitution, the σ-band anisotropy diminishes rapidly.…”