scholarly journals Strong-coupling character of superconducting phase in compressed selenium hydride

2020 ◽  
pp. 2150045
Author(s):  
Ewa A. Drzazga-Szczȩśniak ◽  
Adam Z. Kaczmarek
Keyword(s):  
Critical Temperature ◽  
Strong Coupling ◽  
Magnesium Diboride ◽  
Critical Magnetic Field ◽  
Superconducting Phase ◽  
Weak Coupling Regime ◽  
Superconducting Properties ◽  
Quantitative Characterization ◽  
Coulomb Pseudopotential

At present, metal hydrides are considered highly promising materials for phonon-mediated superconductors that exhibit high values of the critical temperature. In the present study, the superconducting properties of the compressed selenium hydride in its simplest form (HSe) are analyzed, toward quantitative characterization of this phase. By using the state-of-art Migdal-Eliashberg formalism, it is shown that the critical temperature in this material is relatively high ([Formula: see text][Formula: see text]K) and surpasses the level of magnesium diboride superconductor, assuming that the Coulomb pseudopotential takes value of [Formula: see text]. Moreover, the employed theoretical model allows us to characterize other pivotal thermodynamic properties such as the superconducting band gap, the free energy, the specific heat, and the critical magnetic field. In what follows, it is shown that the characteristic thermodynamic ratios for the aforementioned parameters differ from the predictions of the Bardeen-Cooper-Schrieffer theory. As a result, we argue that strong-coupling and retardation effects play important role in the discussed superconducting state, which cannot be described within the weak-coupling regime.

scholarly journals Superconducting properties of under- and over-doped BaxK1−xBiO3 perovskite oxide

2018 ◽  
Vol 32 (16) ◽  
pp. 1850174 ◽  
Author(s):  
D. Szczȩśniak ◽  
A. Z. Kaczmarek ◽  
R. Szczȩśniak ◽  
S. V. Turchuk ◽  
H. Zhao ◽  
...  
Keyword(s):  
Band Gap ◽  
Strong Coupling ◽  
Doping Level ◽  
Critical Magnetic Field ◽  
Superconducting Phase ◽  
Perovskite Oxide ◽  
Pairing Mechanism ◽  
Dimensionless Ratio ◽  
Coulomb Pseudopotential

In this study, we investigate the thermodynamic properties of the Ba[Formula: see text]K[Formula: see text]BiO3 (BKBO) superconductor in the under- (x = 0.5) and over-doped (x = 0.7) regime, within the framework of the Migdal–Eliashberg formalism. The analysis is conducted to verify that the electron–phonon pairing mechanism is responsible for the induction of the superconducting phase in the mentioned compound. In particular, we show that BKBO is characterized by the relatively high critical value of the Coulomb pseudopotential, which changes with doping level and does not follow the Morel–Anderson model. In what follows, the corresponding superconducting band gap size and related dimensionless ratio are estimated to increase with the doping, in agreement with the experimental predictions. Moreover, the effective mass of electrons is found to take on high values in the entire doping and temperature region. Finally, the characteristic dimensionless ratios for the superconducting band gap, the critical magnetic field and the specific heat for the superconducting state are predicted to exceed the limits set within the Bardeen–Cooper–Schrieffer theory, suggesting pivotal role of the strong-coupling and retardation effects in the analyzed compound. Presented results supplement our previous investigations and account for the strong-coupling phonon-mediated character of the superconducting phase in BKBO at any doping level.

scholarly journals Characterization of the superconducting phase in tellurium hydride at high pressure

2019 ◽  
Vol 33 (16) ◽  
pp. 1950169 ◽  
Author(s):  
Tomasz P. Zemła ◽  
Klaudia M. Szczȩśniak ◽  
Adam Z. Kaczmarek ◽  
Svitlana V. Turchuk
Keyword(s):  
High Pressure ◽  
Critical Temperature ◽  
Strong Coupling ◽  
Superconducting State ◽  
Density Functional ◽  
Superconducting Phase ◽  
Bcs Theory ◽  
Electron Mass ◽  
Eliashberg Equations ◽  
Effective Electron

At present, hydrogen-based compounds constitute one of the most promising classes of materials for applications as phonon-mediated high-temperature superconductors. Herein, the behavior of the superconducting phase in tellurium hydride (HTe) at high pressure (p = 300 GPa) is analyzed in detail, by using the isotropic Migdal–Eliashberg equations. The chosen pressure conditions are considered here as a case study which corresponds to the highest critical temperature value [Formula: see text] in the analyzed material, as determined within recent density functional theory simulations. It is found that the Migdal–Eliashberg formalism, which constitutes a strong-coupling generalization of the Bardeen–Cooper–Schrieffer (BCS) theory, predicts that the critical temperature value ([Formula: see text] K) is higher than previous estimates of the McMillan formula. Further investigations show that the characteristic dimensionless ratios for the thermodynamic critical field, the specific heat for the superconducting state, and the superconducting band gap exceed the limits of the BCS theory. In this context, also the effective electron mass is not equal to the bare electron mass as provided by the BCS theory. On the basis of these findings it is predicted that the strong-coupling and retardation effects play pivotal role in the superconducting phase of HTe at 300 GPa, in agreement with similar theoretical estimates for the sibling hydrogen and hydrogen-based compounds. Hence, it is suggested that the superconducting state in HTe cannot be properly described within the mean-field picture of the BCS theory.

Preparation and Characterization of the New Y257 Superconductors

2013 ◽  
Vol 770 ◽  
pp. 22-25 ◽  
Author(s):  
Thitipong Kruaehong
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Critical Temperature ◽  
Solid State ◽  
Superconducting Phase ◽  
Lattice Parameters ◽  
Peritectic Temperature ◽  
Space Group ◽  
Space Groups

The new Y257 superconductor in YBaCuO family was synthesized by standard solid state reaction. The Y257 samples were measured the critical temperature (Tc) by the four-probes method that found at 90 K. The XRD technique and FULLPROF program were used to determine the lattice parameters, space group and phase compositions. It was found that the Y257 exhibited in both of superconducting and non-superconducting phase. The Pmmm space group was fit well on superconducting phase with the lattice parameters as a=3.8108 Å, b=3.8544 Å and c=26.4967 Å. The non-superconducting phase exhibited in two space groups of Pccm (a=12.9770 Å, b=20.54780 Å and c=11.3530 Å) and Im-3m (a= 18.2104 Å, b=18.2104 Å and c=18.2104 Å). The peritectic temperature at 976.73°C was measured by differential thermal analysis.

CRITICAL TEMPERATURES FOR SUPERCONDUCTING QUARK MATTER EXISTENCE IN DENSE STELLAR CORES

1992 ◽  
Vol 07 (11) ◽  
pp. 995-999 ◽  
Author(s):  
J.E. HORVATH ◽  
O.G. BENVENUTO ◽  
H. VUCETICH
Keyword(s):  
Critical Temperature ◽  
Strong Coupling ◽  
Long Range ◽  
Quark Matter ◽  
Superconducting Phase ◽  
Strong Coupling Constant ◽  
Compact Stars ◽  
Coupling Constant ◽  
Critical Temperatures ◽  
Explicit Expressions

If quark matter is actually a component of compact stars it can probably develope a superconducting phase as a result of QCD interactions. This effect may be harmless for (or dramatically affect) the properties of the star, depending on the actual value of the strong coupling constant α c . Explicit expressions for the critical temperature T c are derived by using some recent results on the long-range behavior of the gluon propagators. The consequences for the cooling histories of compact stars and possible trends are briefly discussed.

Phase Evolution and Critical Temperature of MgB2 Superconductor Made of β-Rhombohedral Boron with Temperature Sintering Variation

2020 ◽  
Vol 855 ◽  
pp. 215-220
Author(s):  
Sigit Dwi Yudanto ◽  
Agung Imaduddin ◽  
Budhy Kurniawan ◽  
Azwar Manaf
Keyword(s):  
Electrical Resistivity ◽  
Critical Temperature ◽  
Sintering Temperature ◽  
Phase Evolution ◽  
Superconducting Phase ◽  
Stoichiometric Ratio ◽  
Superconducting Properties ◽  
Conventional Solid State Reaction ◽  
Peak Intensity ◽  
Rhombohedral Boron

We report the phase formation and electrical resistivity of MgB2 superconductor samples. Method of synthesis was conventional solid-state reaction employing crystalline β-rhombohedral boron (B) and magnesium (Mg) with a stoichiometric ratio of Mg:B=1:2. The two precursors were mixed and sintered at various temperatures from 600°C to 900°C for an hour. All samples were characterized employing XRD, SEM, and Cryogenic Magnetometer. It is shown that the MgB2 phase begins to form at a sintering temperature of 700°C. The highest peak intensity of the MgB2 phase was observed in a sample sintered at 900°C indicates the largest fraction of the superconducting phase among all synthesized samples. Electrical resistivity values were carried out to investigate the superconducting properties of the samples. It is also shown the samples sintered at a temperature of 800°C and 900°C possess superconducting properties with a critical temperature of ~ 43 K

Characterization of Y-Ba-Cu-O films grown on silicon substrates by sequential evaporation

1988 ◽  
Vol 46 ◽  
pp. 866-867
Author(s):  
E. L. Hall ◽  
A. Mogro-Campero ◽  
L. G. Turner ◽  
N. Lewis
Keyword(s):  
Thin Film ◽  
Thin Film Deposition ◽  
Superconducting Films ◽  
Electron Beam Evaporation ◽  
Film Deposition ◽  
Silicon Substrates ◽  
Superconducting Properties ◽  
Sequential Electron ◽  
Thin Superconducting Films

There is great interest in the growth of thin superconducting films of YBa2Cu3Ox on silicon, since this is a necessary first step in the use of this superconductor in a variety of possible electronic applications including interconnects and hybrid semiconductor/superconductor devices. However, initial experiments in this area showed that drastic interdiffusion of Si into the superconductor occurred during annealing if the Y-Ba-Cu-O was deposited direcdy on Si or SiO2, and this interdiffusion destroyed the superconducting properties. This paper describes the results of the use of a zirconia buffer layer as a diffusion barrier in the growth of thin YBa2Cu3Ox films on Si. A more complete description of the growth and characterization of these films will be published elsewhere.Thin film deposition was carried out by sequential electron beam evaporation in vacuum onto clean or oxidized single crystal Si wafers. The first layer evaporated was 0.4 μm of zirconia.

Processing and characterization of YBa2Cu3O7−x/Ag composites

1990 ◽  
Vol 48 (4) ◽  
pp. 46-47
Author(s):  
Jafar Javadpour ◽  
Bradley L. Thiel ◽  
Sarikaya Mehmet ◽  
Ilhan A. Aksay
Keyword(s):  
Composite System ◽  
Precursor Solution ◽  
Microstructural Development ◽  
Superconducting Properties ◽  
Practical Applications ◽  
Nitrate Precursor ◽  
Cold Pressed ◽  
Tape Cast ◽  
Composite Samples

Practical applications of bulk YBa2Cu3O7−x materials have been limited because of their inadequate critical current density (jc) and poor mechanical properties. Several recent reports have indicated that the addition of Ag to the YBa2Cu3O7−x system is beneficial in improving both mechanical and superconducting properties. However, detailed studies concerning the effect of Ag on the microstructural development of the cermet system have been lacking. Here, we present some observations on the microstructural evolution in the YBa2Cu3O7−x/Ag composite system.The composite samples were prepared by mixing various amounts (2.5 - 50 wt%) AgNO3 in the YBa2Cu3O7−x nitrate precursor solution. These solutions were then spray dried and the resulting powders were either cold pressed or tape cast. The microstructures of the sintered samples were analyzed using SEM (Philips 515) and an analytical TEM (Philips 430T).The SEM micrographs of the compacts with 2.5 and 50 wt% Ag addition sintered at 915°C (below the melting point of Ag) for 1 h in air are displayed in Figs. 1 and 2, respectively.

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