From LaH10 to room-temperature superconductors.

Thermodynamic parameters of the LaH10 superconductor were an object of our interest. LaH10 is characterised by the highest experimentally observed value of the critical temperature: [Formula: see text] K (pa = 150 GPa) and [Formula: see text] K (pb = 190 GPa). It belongs to the group of superconductors with a strong electron-phonon coupling (λa ~ 2.2 and λb ~ 2.8). We calculated the thermodynamic parameters of this superconductor and found that the values of the order parameter, the thermodynamic critical field, and the specific heat differ significantly from the values predicted by the conventional BCS theory. Due to the specific structure of the Eliashberg function for the hydrogenated compounds, the qualitative analysis suggests that the superconductors of the LaδX1-δH10-type (LaXH-type) structure, where X ∈ {Sc, Y}, would exhibit significantly higher critical temperature than TC obtained for LaH10. In the case of LaScH we came to the following assessments: [Formula: see text] K and [Formula: see text] K, while the results for LaYH were: [Formula: see text] K and [Formula: see text] K.

Influence of external extrusion on stability of hydrogen molecule and its chaotic behavior.

We have determined the stability conditions of the hydrogen molecule under the influence of an external force of harmonic-type explicitly dependent on the amplitude (A) and frequency (Ω). The ground state of the molecule has been determined in the framework of the Born-Oppenheimer approximation, whereas the energy of the electronic subsystem has been calculated using the Hubbard model including all two-site electron interactions. The diagram of RT0 (A,Ω), where RT0 denotes the distance between protons after the fixed initial time T0, allowed us to visualize the area of the instability with the complicated structure. We have shown that the vibrations of the hydrogen molecule have a chaotic nature for some points of the instability region. In addition to the amplitude and frequency of the extrusion, the control parameter of the stability of the molecule is the external force associated with pressure. The increase in its value causes the disappearance of the area of the instability and chaotic vibrations.

Influence of lithium doping on the thermodynamic properties of graphene based superconductors.

The superconducting phase in graphene can be induced by doping its surface with lithium atoms. In this paper, it is shown that the critical temperature (TC) for the LiC6 and Li2C6 compounds changes from 8.55 K to 21.83 K. The other thermodynamic parameters--the order parameter (Δ), the specific heat for the superconducting (C(S)) and the normal (C(N)) state and the thermodynamic critical field (HC)--differ from the predictions of the Bardeen-Cooper-Schrieffer theory. In particular, the ratio RΔ ≡ 2Δ(0)/kBTC is equal to[3.72]LiC6 and [4.21]Li2C6. Additionally, the quantities RC ≡ ΔC(TC)/C(N)(TC) and [Formula: see text] take the values[1.47]LiC6,[1.79]Li2C6 and [0.167]LiC6, [0.144]Li2C6. Finally, it is shown that the electron effective mass at TC is high and equals:[1.61me]LiC6 and [2.12me]Li2C6.