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A. P. Durajski

Publications and source records attributed to A. P. Durajski.

29 records · Page 2Linked to original sources
arXiv2013

Study of the superconducting state in the Cmmm phase of GeH4 compound

A superconducting state, that induces in ${\rm GeH_{4}}$ under the pressure at 20 GPa, is being characterized by a high critical temperature $T_{C}\in<54.54,31.23>$ K, for a wide range of the Coulomb pseudopotential $μ^{\star}\in<0.1,0.3>$. Other thermodynamic parameters for the considered range of the Coulomb pseudopotential significantly differ from the predictions of a classical BCS theory. In particular: (i) the ratio of the energy gap to the critical temperature ($R_Δ\equiv 2Δ(0)/k_{B}T_{C}$) changes from 4.07 to 3.88; (ii) the value of the parameter $R_{C}\equivΔC(T_{C})/C^{N}(T_{C})$ decreases from 1.85 to 1.69, where $ΔC$ denotes the specific heat's jump, and $C^{N}$ is the specific heat of the normal state; (iii) the ratio $R_{H}\equiv T_{C}C^{N}(T_{C})/H^{2}_{C}(0)$, where $H_{C}(0)$ represents the low - temperature thermodynamic critical field, increases from 0.147 to 0.155.

cond-mat.supr-con↗
arXiv2012

CaLi2 superconductor under the pressure of 100 GPa: the thermodynamic critical field and the specific heat

In the paper, the thermodynamic properties of the CaLi$_2$ superconductor have been studied. It has been assumed the high value of the pressure: $p=100$ GPa. The thermodynamic critical field ($H_{C}$) and the specific heats for the superconducting and normal state ($C^{S}$ and $C^{N}$) have been obtained. The calculations have been made within the framework of the Eliashberg approach for the wide range of the Coulomb pseudopotential: $μ^{\star}\in<0.1,0.3>$. It has been shown that the low-temperature critical field and the specific heat jump at $T_{C}$ strongly decrease if $μ^{\star}$ increases. The value of the dimensionless ratio $R_{C}\equiv(C^{S}-C^{N})/C^{N}$ at the critical temperature differs significantly from the value predicted by the BCS model. In particular, the parameter $R_{C}$ decreases from 1.83 to 1.73 with the increase of the Coulomb pseudopotential value. In the paper, the interpolation formulas for the functions $T_{C}(μ^{\star})$ and $R_{C}(μ^{\star})$ have been also given.

cond-mat.supr-con↗
arXiv2012

The characterization of high-pressure superconducting state in Si2H6 compound: the strong-coupling description

The thermodynamic parameters of the superconducting state, that induces in ${\rm Si_{2}H_{6}}$ under the pressure at 275 GPa, have been calculated. In the framework of the Eliashberg formalism, it has been shown that the critical temperature can attain extremely high values: $T_{C}(μ^{\star})\in<173.36, 99.99>$ K, where the Coulomb pseudopotential $(μ^{\star})$ belongs to the range from 0.1 to 0.3. The ratio of the energy gap to the critical temperature ($R_Δ$) significantly exceeds the value predicted by the BCS theory: $R_Δ(μ^{\star})\in<4.40, 4.04>$. Additionally, it has been stated that in the whole range of the superconducting state's existence, the electron effective mass ($m^{\star}_{e}$) is large; $[m^{\star}_{e}]^{\rm max}_{T=T_{C}}=2.397m_{e}$, where the symbol $m_{e}$ denotes the electron band mass.

cond-mat.supr-con↗
arXiv2012

On the critical temperature and the energy gap in dense SiH4(H2)2 at 250 GPa

The critical temperature ($T_{C}$) and the energy gap ($2Δ(T)$) for the superconductor SiH$_4$(H$_2$)$_2$ at 250 GPa have been calculated. The wide range of the Coulomb pseudopotential's values has been considered: $μ^{\star}\in<0.1,0.3>$. It has been stated that $T_{C}$ decreases together with the increase of $μ^{\star}$ from 129.83 K to 81.40 K. The low-temperature energy gap ($T\sim 0$ K) decreases together with the increase of the Coulomb pseudopotential from 50.96 meV to 30.12 meV. The high values of $2Δ(0)$ mean that the dimensionless ratio $R_Δ\equiv 2Δ(0)/k_{B}T_{C}$ significantly exceeds the value predicted by the classical BCS theory. In the considered case: $R_Δ\in<4.55,4.29>$. Due to the unusual dependence of the critical temperature and the energy gap on $μ^{\star}$, the analytical expressions for $T_{C}(μ^{\star})$ and $Δ(μ^{\star})$ have been given.

cond-mat.supr-con↗
arXiv2012

Electron-phonon pairing mechanism: cuprates with high value of the critical temperature

The model for the cuprates based on the modified electron-phonon pairing mechanism has been tested. For this purpose, the superconductors with high value of the critical temperature have been taken into consideration. In particular: ${\rm YBa_{2}Cu_{3}O_{7-y}}$, ${\rm HgBa_{2}CuO_{4+y}}$, ${\rm HgBa_{2}Cu_{1-x}Zn_{x}O_{4+y}}$, and ${\rm HgBa_{2}Ca_{2}Cu_{3}O_{8+y}}$. It has been shown that the dependence of the ratio $R_{1}\equiv 2Δ_{tot}^{(0)}/k_{B}T_{C}$ on the doping ($p$) can be properly predicted in the framework of the presented theory; the symbol $Δ_{tot}^{(0)}$ denotes the energy gap amplitude at the temperature of zero Kelvin, and $T_{C}$ is the critical temperature. The numerical results have been supplemented by the formula which describes the function $R_{1}(p)$.

cond-mat.supr-con↗
arXiv2012

The superconducting phase of Calcium under the pressure at 200 GPa: the strong-coupling description

The thermodynamic parameters of the superconducting state in Calcium under the pressure at 200 GPa have been determined. The numerical analysis by using the Eliashberg equations in the mixed representation has been conducted. It has been stated, that the critical temperature ($T_{C}$) decreases from 36.15 K to 20.79 K dependently on the assumed value of the Coulomb pseudopotential ($μ^{*}\in<0.1,0.3>$). Next, the order parameter near the temperature of zero Kelvin ($Δ(0)$) has been obtained. It has been proven, that the dimensionless ratio $2Δ(0)/k_{B}T_{C}$ decreases from 4.25 to 3.90 together with the growth of $μ^{*}$. Finally, the ratio of the electron effective mass to the electron bare mass ($m^{*}_{e}/m_{e}$) has been calculated. It has been shown, that $m^{*}_{e}/m_{e}$ takes the high value in the whole range of the superconducting phase's existence, and its maximum is equal to 2.23 for T=T_{C}.

cond-mat.supr-con↗
arXiv2011

Thermodynamics of the superconducting state in Calcium at 200 GPa

The thermodynamic parameters of the superconducting state in Calcium under the pressure at 200 GPa were calculated. The Coulomb pseudopotential values ($μ^{\star}$) from 0.1 to 0.3 were taken into consideration. It has been shown, that the specific heat's jump at the critical temperature and the thermodynamic critical field near zero Kelvin strongly decrease with $μ^{\star}$. The dimensionless ratios $r_{1}\equiv ΔC(T_{C})/C^{N}(T_{C})$ and $r_{2}\equiv T_{C}C^{N}(T_{C})/H^{2}_{C}(0)$ significantly differ from the predictions based on the BCS model. In particular, $r_{1}$ decreases from 2.64 to 1.97 with the Coulomb pseudopotential; whereas $r_{2}$ increases from 0.140 to 0.157. The numerical results have been supplemented by the analytical approach.

cond-mat.supr-con↗
arXiv2011

Superconductivity of calcium under the pressure at 120 GPa

The properties of the superconducting state in calcium under the pressure at 120 GPa were analyzed. By using the imaginary axis Eliashberg equations it has been shown, that the Coulomb pseudopotential reaches the high value equal to 0.215. In the considered case, the critical temperature is not properly described by the Allen-Dynes formula and it should be calculated with an use of the modified expression. In the paper the exact solutions of the Eliashberg equations on the real axis were also obtained. On this basis it was stated, that the effective potential of the electron-electron interaction is attractive for the frequencies lower or equal to the maximum phonon frequency. Then, the dimensionless parameter 2Δ(0)/k_{B}T_{C}=4.10 was calculated. In the last step it has been proven, that the ratio of the electron effective mass to the bare electron mass is high and reaches its maximum equal to 2.36 for the critical temperature.

cond-mat.supr-con↗
arXiv2011

Properties of the superconducting state in compressed Sulphur

The thermodynamic properties of the superconducting state in Sulphur under the pressure at 160 GPa were determined. It has been shown that: (i) the critical value of the Coulomb pseudopotential is equal to 0.127; (ii) the critical temperature (T_{C} =17 K) should be calculated by using the modified Allen-Dynes formula; (iii) the effective electron-electron interaction is attractive in the range of frequencies from zero to the frequency slightly lesser than the maximum phonon frequency (~ 0.85Ω_{max}); (iv) the dimensionless ratios 2Δ(0)/k_{B}T_{C}, $ΔC(T_{C})/C^{N}(T_{C}) and T_{C}C^{N}(T_{C})/H^{2}_{C}(0) are equal to 3.7, 1.65 and 0.16 respectively; (v) the ratio of the effective to bare electron mass reaches maximum of 1.77 for T=T_{C}.

cond-mat.supr-con↗
arXiv2011

Specifc Heat and Thermodynamic Critical Field for Calcium under the Pressure at 120 GPa

The free energy difference between the superconducting and normal state for Calcium under the pressure at 120 GPa has been determined. The numerical calculations have been made in the framework of the imaginary axis Eliashberg approach. On the basis of the obtained results the specific heat in the superconducting C^{S}(T) and normal C^{N}(T) state, as well as, the thermodynamic critical field H_{C}(T) have been obtained. It has been shown that the characteristic values of the considered thermodynamic quantities do not obey the BCS universal laws. In particular, ΔC(T_{C})/C^N(T_{C})=2.48 and T_{C}C^{N}(T_{C})/H_{C}^{2}(0)=0.154.

cond-mat.supr-con↗