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1
Content available remote

Synthesis and Characterization of the Superconductor Mo_3Sb_7

100%
Tran V., Bukowski Z.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
67-74
EN
We synthesized a polycrystalline sample of the superconductor Mo_3Sb_7 and characterized its basic properties by measurements of magnetization, electrical resistivity and specific heat. The measurements establish a superconducting phase transition at T_c=2.25 (0.05) K. In applied magnetic fields, the magnetization and resistivity show the behavior of type-II superconductor. From the specific heat measurement, the electronic specific heat coefficient,γ, specific heat jump at T_c, ΔC(T_c)/γT_c, and the Debye temperature Θ_D, are evaluated to be 34.5 mJ/(mol K^2), 1.56 and 283 K, respectively. From analysis of the specific heat data we suggest that this compound belongs to an intermediate strong coupling regime in the BCS context. The observed enhancement in theγ-value suggests a substantial contribution of Mo-4d-electrons to the density of states. Our experimental data do not support interpretation of superconductivity in Mo_3Sb_7 in terms of neither unconventional superconductivity or spin fluctuations proposed previously.
2
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AC Microcalorimetry of Superconducting MgCNi_3 Single Crystals

100%
Kačmarčík J., Pribulová Z., Samuely P., Marcenat C., Klein T., Jang D., Lee H., Lee H., Lee S.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
363-366
EN
The low-temperature specific heat of single-crystal samples of superconducting MgCNi_3 with typical dimensions 200 μm were measured for the first time. A computer controlled ac microcalorimeter using an optical fiber and an infrared light-emitting diode as the heat source was used down to 2 K at magnetic fields up to 8 T. The specific heat data suggest a moderate coupling in MgCNi_3.
3
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Specific Heatof the Filled Skutterudite Superconductor LaOs₄As₁₂

100%
Juraszek J., Henkie Z., Cichorek T.
Acta Physica Polonica A
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2016
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vol. 130
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issue 2
597-599
EN
We investigated low-temperature specific heat of the filled skutterudite compound LaOs₄As₁₂ with a transition temperature T_{c} = 3.2 K. A moderate size of a specific-heat jump points at a weak electron-phonon coupling in this material. At T < T_{c}, the electronic contribution to the specific heat was found to be at variance with the predictions for an s-wave superconductor with one energy gap. Additionally, we observed an upward curvature of the upper critical field near the transition temperature. Both features provide some indications towards multiband superconductivity, although anisotropy effects as a viable cause of the observed anomalies in LaOs₄As₁₂ cannot be excluded. Similarities to a probable two-band superconductor LaRu₄As₁₂ are discussed.
4
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Two-Gap Superconductivity in 2H-NbS_2

100%
Pribulová Z., Leroux M., Kačmarčík J., Marcenat C., Klein T., Rodière P., Cario L., Samuely P.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
1024-1025
EN
We performed specific heat measurements of the superconducting single crystal of 2H-NbS_2 in the temperature range down to 0.6 K and magnetic fields up to 14 T. The temperature and magnetic field dependence of the electronic specific heat consistently indicate existence of two superconducting energy gaps in the system. The superconducting anisotropy depends on both temperature and magnetic field. Moreover, the angular dependence of the upper critical field deviates from the Ginzburg-Landau behavior and rather reminds that of MgB_2. All these features point to a multigap superconductivity in 2H-NbS_2. Our measurements are in a perfect agreement with the previous scanning tunneling spectroscopy of Guillamón et al.
5
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Studies on Isotope Shift Exponent and Pressure Coefficient for Extended Superconductors within BCS Formalism

80%
Banerjee B., Roy S.
Acta Physica Polonica A
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2009
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vol. 115
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issue 5
914-919
EN
A tight-binding model comprising a hopping and an attractive interaction term was considered for high temperature superconductors. Explicit calculations on the effects of isotopic substitution of atoms and application of pressure on the transition temperatures were made in this work. Exact analytical expressions for the isotope-shift exponent (α) and pressure coefficient (γ_P) of transition temperature (T_C) considering the isotopic mass and pressure dependence of the hopping and attractive interaction strengths from a minimal model describing superconductivity were obtained. Theoretical predictions for α and γ_P with proper choice of parameters are found to be qualitatively consistent with the results of the experiments of high T_C oxides. The results depend on the band dispersion chosen.
6
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Monte Carlo Study of a Periodically Pinned 2D Superconductor

80%
Rezlescu N., Anghelache R., Ciobotaru I.
Acta Physica Polonica A
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1997
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vol. 91
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issue 2
337-340
EN
We show that a natural assumption on the moving mechanism of vortices in a periodically pinned, two-dimensional superconductor in the mixed state is the basis for a n-clock-like model. The pinning points are considered to be centered in each unit cell of the superconducting lattice. This property enables one to use a discrete version of the XY model used in the simulations focusing on the melting of the Abrikosov lattice of vortices in a system of Josephson arrays. A Monte Carlo study performed on the corresponding Hamiltonian in a field given by a filling factor of f=1/2 exhibits two phase transitions, at the temperatures T_{c1}≈0.325 and T_{m}≈0.65. The numerical estimation of the Challa parameters for both transitions indicates their continuous nature. The physical meaning of the lower transition is the expulsion of the magnetic field from the superconducting system, i.e. the Meissner effect. The physical equivalent of the upper transition is the melting of the pinned vortex lattice.
7
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On the Magnetic Penetration Depth in Superconducting Ultrathin Lead Films

80%
Durajski A., Szczęśniak R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1051-1053
EN
In the present paper, we report a theoretical study of the magnetic London penetration depth in ultrathin Pb films consisting of five to ten monolayers. Our calculations were performed within the framework of the strong-coupling approach. We observed that for thin films, the thermodynamic parameter exhibits an oscillatory behaviour connected with a quantum size effect. Moreover, we proved that the London penetration depth of Pb films cannot be correctly described using the Bardeen-Cooper-Schrieffer theory of superconductivity due to the strong-coupling and retardation effects. The Eliashberg theory, used in this paper, goes beyond the BCS theory to include these effects which allows to describe the superconducting state on the quantitative level.
8
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Pressure Dependence of the Thermodynamic Critical Field in Francium

80%
Pach P., Szczęśniak R., Durajski A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
231-233
EN
In the paper, the values of the thermodynamic critical field (H_{C}) for francium have been calculated. It has been assumed the wide range of the pressure: p∈ ⟨7.2; 14⟩ GPa. The analysis has been performed in the framework of the strong-coupling formalism. It has been predicted that the value of the ratio H_{C}(0)/√ρ(0) increases with the increasing pressure from 3.08 meV to 5.84 meV, where ρ(0) denotes the electron density of states at the Fermi level. The dimensionless parameter T_{C}C^{N}(T_{C})/H²_{C}(0) is smaller than in the BCS theory and decreases with pressure from 0.150 to 0.141. The symbol T_{C} represents the critical temperature and C^{N} is the specific heat for the normal state.
9
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Characterization of Novel High-Pressure Close-Packed Superconducting Phase of Boron

80%
Szczęśniak D., Szczęśniak R.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
254-256
EN
We report study on the thermodynamic properties of the novel high-pressure superconducting phase of boron with hexagonal P6₃/mcm structure. Our analysis is conducted at the pressure of p=400 GPa, which is motivated by the highest value of the superconducting transition temperature (T_{C}) observed previously under such conditions for the P6₃/mcm boron. Our investigations of the thermodynamic properties are performed within the Eliashberg formalism, due to the strong-coupling character of the considered material. In particular, we calculate the thermodynamic properties of the superconducting state which allows us to determine the values of the characteristic dimensionless parameters; the zero-temperature energy gap to the critical temperature, the ratio of the specific heats, as well as the ratio connected with the zero-temperature thermodynamic critical field.
10
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Specific Heat Study of Superconductivity in Cu_{0.061}TiSe_{2}

80%
Kačmarčík J., Pribulová Z., Pal'uchová V., Husaníková P., Karapetrov G., Komanický V., Samuely P.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
322-323
EN
In TiSe_{2} a charge-density-waves order is continuously suppressed by copper doping and superconductivity appears. We report a calorimetric study performed on the superconducting single crystal of Cu_{0.061}TiSe_{2} with T_{c}=2.8 K, measured by the ac technique at low temperatures down to 0.6 K and magnetic fields up to 2 T. Sharp specific heat anomaly at the superconducting transition is found. The temperature dependence of the electronic specific heat and the angular dependence of the critical temperature, measured at a fixed magnetic field, consistently indicate on the existence of a single s-wave superconducting gap with a coupling strength of 2Δ/k_{B}T_{c}=3.6, close to BCS limit.
11
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Characteristics of the Eliashberg Formalism on the Example of High-Pressure Superconducting State in Phosphor

80%
Duda A., Szczęśniak R., Sowińska M., Domagalska I.
Acta Physica Polonica A
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2016
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vol. 130
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issue 2
649-654
EN
The work describes the properties of the high-pressure superconducting state in phosphor: p∈ {20, 30, 40, 70} GPa. The calculations were performed in the framework of the Eliashberg formalism, which is the natural generalization of the BCS theory. The exceptional attention was paid to the accurate presentation of the used analysis scheme. With respect to the superconducting state in phosphor it was shown that the observed not-high values of the critical temperature ([T_{C}]_{p=30GPa}^{max}=8.45 K) result not only from the low values of the electron-phonon coupling constant, but also from the very strong depairing Coulomb interactions. Additionally the inconsiderable strong-coupling and retardation effects force the dimensionless ratios R_{Δ}, R_{C}, and R_{H} - related to the critical temperature, the order parameter, the specific heat, and the thermodynamic critical field - to take the values close to the BCS predictions.
12
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Remarks on the First Hundred Years of Superconductivity

80%
Wysokiński K.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
721-725
EN
On the occasion of centenary of superconductivity discovery I recall some facts from the first period and attempts to understand the phenomenon. It turns out that most famous physicists of the first half of XX century have tried to solve the puzzle. Bardeen, Cooper and Schrieffer succeeded in 1957. The BCS theory successfully described all known facts and offered new predictions, which soon have been confirmed experimentally contributing to the widespread acceptance of the theory. It have found applications in nuclear physics, theory of neutron stars and cold atomic gases. The discoveries of new superconductors in the last thirty years show that simple BCS model is not enough to understand new unconventional superconductors. The studies of superconductors develop vividly and still fascinate new generations of physicists working in such diverse fields as material science and string theory.
13
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Content available

The Isotope Effect of Disordered Superconductors

80%
Mierzyńska M., Wysokiński K.
Acta Physica Polonica A
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2004
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vol. 106
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issue 5
647-652
EN
The isotope effects in disordered weak and strong coupling superconductors of different symmetries of the order parameter have been studied. We have found that even though weak localisation corrections to Eliashberg equations describe a strong degradation of transition temperature with disorder of s-wave superconductors, their influence on isotope coefficient is relatively weak. On the other hand the calculated change of relative isotope coefficient with T_c/T_{c0} in homogeneous thin film materials is similar to that observed in high temperature superconductors.
14
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On the Thermodynamic Critical Field for the K_3C_{60} and Rb_3C_{60} Fullerides

80%
Durajski A., Szczęśniak R.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
342-343
EN
In the paper the temperature dependence of the thermodynamic critical field (H_c) for the alkali-metal-doped fullerides K_3C_{60} and Rb_3C_{60} has been considered. The numerical calculations have been conducted in the framework of the Migdal-Eliashberg formalism. It has been shown that the obtained numerical values of H_c agree with the experimental data. Finally, the dimensionless ratio: R_{H} ≡ T_cC^{N} (T_c)/H^{2}_c(0) has been calculated, where T_c is the critical temperature and C^{N} denotes the specific heat in the normal state. The theoretical analysis has proved that for the considered fullerides the parameter R_{H} is beyond the BCS prediction. In particular: R_{H}=0.143 for K_3C_{60}, and R_{H}=0.145 for Rb_3C_{60}.
15
Content available remote

Thermodynamic Critical Magnetic Field for Chlorine Halide Superconductor at High Pressure

80%
Szczęśniak D., Szczęśniak R.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
344-345
EN
At present, hydrides are considered as a one of the most interesting high-temperature superconductors with the classical electron-phonon pairing mechanism. In the present paper, we have analyzed the dependence of the thermodynamic critical magnetic field (H_c) on the temperature for the chlorine halide superconductor. The calculations have been made in the framework of the Eliashberg formalism for the following pressure values: p_{1}=320 GPa and p_{2}=360 GPa. We have shown that H_c increases strongly with the increase of the pressure: [H_c(0)]_{p_{2}}/[H_c(0)]_{p_{1}}= 1.43. Furthermore, the dimensionless ratio: R_{H} ≡ T_cC^{N}(T_c)/H_c^{2}(0), where T_c and C^{N} denote the critical temperature and the specific heat of the normal state, differs from the value predicted by the Bardeen-Cooper-Schrieffer theory. In particular: [R_{H}]_{p_{1}}=0.166 and [R_{H}]_{p_{2}}=0.158.
16
Content available remote

The Properties of the Superconducting State in YNi_2B_2C: The One-Band Eliashberg Approach

80%
Jarosik M., Szczęśniak R.
Acta Physica Polonica A
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2011
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vol. 119
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issue 6
863-867
EN
The basic thermodynamic parameters of the superconducting state in YNi_2 B_2 C were calculated in the framework of the one-band Eliashberg model. The effective Eliashberg function, determined on the basis of the transport function, was used during calculations. It was shown that the dimensionless ratios are equal to: R_1 ≡ 2Δp(0)/k_{B} T_{C} = 3.87, R_2 ≡ ΔC(T_{C})/C^{N}(T_{C}) = 1.79 and R_3 ≡ T_{C} C^{N}(T_{C}) / H_{C}^2(0) = 0.159. The value R_1 fairly agrees with the experimental data whereas R_2 and R_3 agree very well.
17
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The Thermodynamic Critical Field οf YNi_2B_2C Superconductor

80%
Jarosik M., Szczęśniak R., Szczęśniak D.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
1031-1033
EN
In the presented work the dependence of the thermodynamic critical field (H_{C}) on the temperature for the YNi_2B_2C superconductor was determined in the framework of the Eliashberg formalism. The numerical calculations were conducted with the use of the modified transport Eliashberg function. It has been stated that the normalized field function H_{C}(T)/H_{C}(0) correctly reproduces the experimental data.
18
Content available remote

Strong-Coupling Description of the High-Temperature Superconductivity in the Molecular Hydrogen

80%
Szczęśniak R., Jarosik M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
841-844
EN
The detailed study of the selected thermodynamic properties of the superconducting phase in the molecular hydrogen under the pressure at 428 GPa has been presented. For the increasing value of the Coulomb pseudopotential μ^{*}∈〈0.08,0.15〉, the following results have been obtained: (i) the critical temperature decreases from 179 K to 141 K, (ii) the ratio R_{1}≡ 2Δ(0)/k_{B}T_{C} differs noticeably from the BCS value: R_{1}∈〈4.71,3.60〉; (iii) the electron effective mass is large and grows slightly together with the temperature ([m^{*}_{e}/m_{e}]_{max}=2.2 for T = T_{C}).
19
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Reversible Magnetization of Melt-Processed NEG-123 Superconductor

80%
Jirsa M., Rameš M., Muralidhar M., Kacmarcik J., Marcenat C.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
1022-1023
EN
Specific heat of superconducting electrons was measured in a melt-processed (Nd_{0.33}Eu_{0.38}Gd_{0.28})Ba_2Cu_3O_{y} superconductor (NEG-123) with 5 mol% of Gd-211, 1 wt% Ag, and 0.035 mol% of Zn. The thermodynamic characteristics of this compound are still not well known. From calorimetric measurements the reversible magnetization, critical fields, penetration depth, and coherence length were deduced. In the vicinity of T_{c}, the reversible magnetic moment was additionally measured by means of SQUID.
20
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Superconducting Parameters of Spinel CuRh₂S₄ under Pressure

80%
Ito M., Taira A., Sonoda K.
Acta Physica Polonica A
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2017
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vol. 131
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issue 6
1450-1453
EN
We investigated the magnetic properties of chalcogenide-spinel superconductor CuRh₂S₄ under pressure and estimated the pressure dependence of the superconducting parameters. With increasing pressure, the superconducting transition temperature (T_{c}), thermodynamic critical field (H_{c}), upper critical field (H_{c2}), penetration depth (λ), and GL parameter (κ) increase. Meanwhile, the lower critical field (H_{c1}) is unchanged and the Ginzburg-Landau coherence length (ξ_{GL}) is reduced by pressurization. The increasing value of κ indicates enhanced characteristics of the type-II superconductor CuRh₂S₄.
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