arXiv subjects

Radosław Szczęśniak

Publications and source records attributed to Radosław Szczęśniak.

3 recordsLinked to original sources

arXiv2020

Superconductivity of $LaH_{10}$ and $LaH_{16}$ polyhydrides

We explore high-pressure phase stability and superconductivity of lanthanum hydrides $LaH_m$ (m=4-11,16). We predict stability of a hitherto unreported polyhydride $P6/mmm$-$LaH_{16}$ at pressures above 150 GPa; at 200 GPa its predicted superconducting $T_C$ is 156 K, critical field $μ_0$$H_C$(0) ~ 35 T and superconducting gap is up to 35 meV. We revisit superconductivity of the recently discovered $LaH_{10}$ and find its $T_C$ to be up to 259 K (170 GPa) from solving the Eliashberg equation and 271 K from solving the gap equation in SCDFT which also allowed us to compute the Coulomb pseudopotential $μ^*$ for $LaH_{10}$ and $LaH_{16}$. Presence of several polymorph modifications of LaH10 may explain the variety in the experimentally measured $T_C$ values for $LaH_{10}$ [1,2]

cond-mat.supr-con↗

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

Anomalously high value of Coulomb pseudopotential for the $\rm H_{5}S_{2}$ superconductor

The ${\rm H_{5}S_{2}}$ and ${\rm H_{2}S}$ compounds are the two candidates for the low-temperature phase of compressed sulfur-hydrogen system. We have shown that the value of Coulomb pseudopotential ($μ^{\star}$) for ${\rm H_{5}S_{2}}$ ($\left[T_{C}\right]_{\rm exp}=36$~K and $p=112$~GPa) is anomalously high. The numerical results give the limitation from below to $μ^{\star}$ that is equal to $0.402$ ($μ^{\star}=0.589$, if we consider the first order vertex corrections to the electron-phonon interaction). Presented data mean that the properties of superconducting phase in the ${\rm H_{5}S_{2}}$ compound can be understood within the classical framework of Eliashberg formalism only at the phenomenological level ($μ^{\star}$ is the parameter of matching the theory to the experimental data). On the other hand, in the case of ${\rm H_{2}S}$ it is not necessary to take high value of Coulomb pseudopotential to reproduce the experimental critical temperature relatively well ($μ^{\star}=0.15$). In our opinion, ${\rm H_{2}S}$ is mainly responsible for the observed superconductivity state in the sulfur-hydrogen system at low temperature.

cond-mat.supr-con↗