Ewa A. Drzazga | Searcharxiv

arXiv2018

Anisotropy effects on the critical magnetic field in CaC$_{6}$ superconductor

The calcium intercalated graphite (CaC$_{6}$) is considered to be a representative material of the graphite intercalated superconductors, which exhibits sizable anisotropy of the Fermi surface (FS). Herein, the influence of the FS anisotropy on the critical magnetic field ($H_{C}$) in CaC$_{6}$ superconductor is comprehensively analyzed within the Migdal-Eliashberg (M-E) formalism. To precisely account for the mentioned anisotropy effects, the analysis is conducted in the framework of the six-band approximation, hitherto not employed for calculations of the $H_{C}$ function in CaC$_{6}$ material. For convenience, the obtained results are compared with the available one- and three-band estimates reported by using the M-E theory. A notable signatures of the increased number of bands are observed for the temperature dependent $H_{C}$ functions. In particular, the $H_{C}$ function decreases at T=0 K as the number of the considered bands is higher. Moreover, it is argued that the six-band formalism yields the most physically relevant shape of the $H_{C}$ function among all considered approximations. Therefore, the six-band model introduces not only quantitative but also qualitative changes to the results, in comparison to the other discussed FS approximations. This observation supports postulate that the six-band model constitutes minimal structure for FS of CaC$_{6}$, but also magnify importance of anisotropy effects for the critical magnetic field calculations.

cond-mat.supr-con↗

arXiv2018

The thermodynamic critical field and specific heat of superconducting state in phosphorene under strain

In this work we present the thermodynamic properties of the superconducting state in phosphorene. In particular, we have examined the electron doped ($n_{D}=1.3\times 10^{14} \rm{cm^{-2}}$) and biaxially strained (4 %) monolayer of black phosphorous, which exhibits best thermodynamic stability and highest superconducting critical temperature ($T_{c}$) among all monolayer phosphorene structures. Due to the confirmed electron-phonon pairing mechanism and relatively high electron-phonon coupling constant in the studied material, we carried out the calculations in the framework of the Eliashberg formalism for a wide range of the Coulomb pseudopotential $μ^{\star}\in\langle 0.1, 0.3\rangle$. We have determined the thermodynamic critical field ($H_{c}$), and the specific heat difference ($ΔC$) between superconducting ($C^{S}$) and normal state ($C^{N}$) as the functions of the temperature. In addition, we have calculated the dimensionless parameters $R_{C}=ΔC(T_{c})/C^{N}(T_{c})$ and $R_{H}=T_{c}C^{N}(T_{c})/H^{2}_{c}(0)$, and also found their significant deviation from the expectations of the BCS theory. In particular, $R_{C} \simeq \langle 2.724, 1.899\rangle$ and $R_{H} \simeq \langle 0.133, 0.155\rangle$ for $μ^{\star}\in \langle 0.1, 0.3\rangle$.

cond-mat.supr-con↗