arXiv subjects

Radoslaw Szczesniak

Publications and source records attributed to Radoslaw Szczesniak.

3 recordsLinked to original sources

arXiv2026

Theoretical prediction of strong-coupling superconductivity in a hypothetical NaAlH3 phase at ambient pressure

We present a comprehensive first-principles investigation of a hypothetical cubic Pm-3m phase of the ternary hydride NaAlH3, focusing on its lattice dynamics, electronic structure, and electron-phonon-mediated superconducting properties at ambient pressure. Using density functional theory and the Migdal-Eliashberg formalism, we find an exceptionally strong electron-phonon coupling ($λ=2.23$), resulting in a superconducting critical temperature of up to 73.7 K for a Coulomb pseudopotential $μ^* = 0.1$. Phonon dispersion calculations, complemented by ab initio molecular dynamics simulations, indicate dynamic and thermal stability within the adopted theoretical framework. The electronic structure exhibits a metallic character with substantial contributions from Al- and Na-derived states at the Fermi level. The resulting superconducting gap ratio ($2Δ(0)/k_B T_c \approx 4.8$) and specific heat jump ($ΔC/γT_c \approx 2.2$) significantly exceed BCS weak-coupling predictions, highlighting the strong-coupling nature of superconductivity in this hypothetical phase.

cond-mat.supr-con↗

arXiv2020

Isotope effect in superconducting lanthanum hydride under high compression

Recently, the discovery of room-temperature superconductivity (SC) was experimentally realized in the fcc phase of LaH$_{10}$ under megabar pressure. Specifically, the isotope effect of $T_{\rm c}$ was measured by the replacement of hydrogen (H) with deuterium (D), demonstrating a driving role of phonons in the observed room-temperature SC. Herein, based on the first-principles calculations within the harmonic approximation, we reveal that (i) the identical electron-phonon coupling constants of fcc LaH$_{10}$ and LaD$_{10}$ decrease monotonously with increasing pressure and (ii) the isotope effect of $T_{\rm c}$ is nearly proportional to $M^{-α}$ ($M$: ionic mass) with $α$ ${\approx}$ 0.465, irrespective of pressure. The predicted value of $α$ agrees well with the experimental one ($α=0.46$) measured at around 150 GPa. Thus, our findings provide a theoretical confirmation of the conventional electron-phonon coupling mechanism in a newly discovered room-temperature superconductor of compressed LaH$_{10}$.

cond-mat.supr-con↗

arXiv2015

Non-BCS thermodynamic properties of H2S superconductor

The present paper determines the thermodynamic properties of the superconducting state in the ${\rm H_{2}S}$ compound. The values of the pressure from $130$ GPa to $180$ GPa were taken into consideration. The calculations were performed in the framework of the Eliashberg formalism. In the first step, the experimental course of the dependence of the critical temperature on the pressure was reproduced: $T_{C}\in\left<31,88\right>$ K, whereas the Coulomb pseudopotential equal to $0.15$ was adopted. Next, the following quantities were calculated: the order parameter at the temperature of zero Kelvin ($Δ\left(0\right)$), the specific heat jump at the critical temperature ($ΔC\left(T_{C}\right)\equiv C^{S}\left(T_{C}\right)-C^{N}\left(T_{C}\right)$), and the thermodynamic critical field ($H_{C}\left(0\right)$). It was found that the values of the dimensionless ratios: $R_Δ\equiv 2Δ(0)/k_{B}T_{C}$, $R_{C}\equiv{ΔC\left(T_{C}\right)}/{C^{N}\left(T_{C}\right)}$, and $R_{H}\equiv{T_{C}C^{N}\left(T_{C}\right)}/{H_{C}^{2}\left(0\right)}$ deviate from the predictions of the BCS theory: $R_Δ\in\left<3.64,4.16\right>$, $R_{C}\in\left<1.59,2.24\right>$, and $R_{H}\in\left<0.144, 0.163\right>$. Generalizing the results on the whole family of the ${\rm H_{n}S}$-type compounds, it was shown that the maximum value of the critical temperature can be equal to $\sim 290$ K, while $R_Δ$, $R_{C}$ and $R_{H}$ adopt the following values: $6.53$, $3.99$, and $0.093$, respectively.

cond-mat.supr-con↗