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 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 Role of Bi3+ ions on structural, optical, photoluminescence and electrical performance of Cd0.9-xZn0.1BixS QDs

2021 ◽  
Vol 3 (7) ◽  
Author(s):  
A. Krishnamoorthy ◽  
P. Sakthivel ◽  
I. Devadoss ◽  
V. M. Anitha Rajathi
Keyword(s):  
Band Gap ◽  
Optical Band Gap ◽  
Optical Transmittance ◽  
Electrical Performance ◽  
Chemical Route ◽  
Red Emission ◽  
The Mean ◽  
Cubic Structure ◽  
Cyclic Voltammetry Analysis

AbstractIn this work, the Cd0.9-xZn0.1BixS QDs with different compositions of Bi3+ ions (0 ≤ x ≤ 0.05) were synthesized using a facile chemical route. The prepared QDs were characterized for analyzing the structural, morphological, elemental, optical, band gap, photoluminescence and electrochemical properties. XRD results confirmed that the Cd0.9-xZn0.1BixS QDs have a cubic structure. The mean crystallite size was increased from ~ 2 to ~ 5 nm for the increase of Bi3+ ions concentration. The optical transmittance behavior was decreased with increasing Bi3+ ions. The scanning electron microscope images showed that the prepared QDs possessed agglomerated morphology and the EDAX confirmed the presence of doped elements as per stoichiometry ratio. The optical band gap was slightly blue-shifted for initial substitution (Bi3+  = 1%) of Bi3+ ions and red-shifted for further increase of Bi3+ compositions. The optical band gap was ranged between 3.76 and 4.0 eV. High intense red emission was received for Bi3+ (1%) doped Zn:CdS QDs. The red emission peaks were shifted to a higher wavelength side due to the addition of Bi3+ ions. The PL emission on UV-region was raised for Bi3+ (1%) and it was diminished. Further, a violet (422 nm) and blue (460 nm) emission were received for Bi3+ ions doping. The cyclic voltammetry analysis showed that Bi3+ (0%) possessed better electrical properties than other compositions of Bi3+ ions.

The Role of a Second Reservoir in an Open BCS Model

2005 ◽  
Vol 12 (04) ◽  
pp. 401-420 ◽  
Author(s):  
F. Bagarello
Keyword(s):  
Critical Temperature ◽  
Superconducting Phase ◽  
Bcs Model ◽  
Stochastic Limit

In this paper we use the stochastic limit approach (SLA) in order to analyze some generalized versions of the open BCS model first introduced by Buffet and Martin and recently analyzed by the author using the SLA. In particular, considering different models, we discuss the role of a second reservoir interacting with the first one (but not with the system) in the computation of the critical temperature corresponding to the transition from a normal to a superconducting phase.

STABILIZATION OF Bi(2223) SUPERCONDUCTING PHASE BY VANADIUM OXIDE ADDITION

1993 ◽  
Vol 07 (01n03) ◽  
pp. 157-161 ◽  
Author(s):  
D. SURESH BABU ◽  
G. NARSING RAO ◽  
L. BROHAN ◽  
M. GANNE
Keyword(s):  
Critical Current Density ◽  
Current Density ◽  
Flux Pinning ◽  
Volume Fraction ◽  
Ac Susceptibility ◽  
Superconducting Phase ◽  
Nominal Composition ◽  
Oxide Addition ◽  
Probable Role

We report on the ac susceptibility, microwave absorption and dc magnetization of Bi 2− x V x Sr 2 Ca 2 Cu 3 O y (nominal composition). The low T c (2212) phase ( T c = 85 K ) dominates in the x = 0 sample with extremly weak flux pinning. In x = 0.4 sample, both flux pinning and volume fraction of the high T c (2223) phase ( T c = 105 K ) were increased. The intragrain critical current density of the sample with x = 0.4 was estimated and found to be comparable with that of Pb doped Bi 2 Sr 2 Ca 2 Cu 3 O y superconductor. The data suggest that addition of V 2 O 5 in Bi 2 Sr 2 Ca 2 Cu 3 O y system increases the volume fraction of the high T c phase. Probable role of vanadium in enhancing the high T c (2223) phase in Bi-V-Sr-Ca-Cu-O system is discussed.

Role of Surface Band Gap Widening in Cu(In, Ga)(Se, S)2 Thin-Films for the Photovoltaic Performance of ZnO/CdS/Cu(In, Ga)(Se, S)2 Heterojunction Solar Cells

2003 ◽  
Vol 763 ◽  
Author(s):  
U. Rau ◽  
M. Turcu
Keyword(s):  
Thin Films ◽  
Surface Layer ◽  
Solar Cells ◽  
Fermi Level ◽  
Band Gap ◽  
Photovoltaic Performance ◽  
Heterojunction Solar Cells ◽  
Fermi Level Pinning ◽  
Device Efficiency

AbstractNumerical simulations are used to investigate the role of the Cu-poor surface defect layer on Cu(In, Ga)Se2 thin-films for the photovoltaic performance of ZnO/CdS/Cu(In, Ga)Se2 heterojunction solar cells. We model the surface layer either as a material which is n-type doped, or as a material which is type-inverted due to Fermi-level pinning by donor-like defects at the interface with CdS. We further assume a band gap widening of this layer with respect to the Cu(In, Ga)Se2 bulk. This feature turns out to represent the key quality of the Cu(In, Ga)Se2 surface as it prevents recombination at the absorber/CdS buffer interface. Whether the type inversion results from n-type doping or from Fermi-level pinning is only of minor importance as long as the surface layer does not imply a too large number of excess defects in its bulk or at its interface with the normal absorber. With increasing number of those defects an n-type layer proofs to be less sensitive to material deterioration when compared to the type-inversion by Fermi-level pinning. For wide gap chalcopyrite solar cells the internal valence band offset between the surface layer and the chalcopyrite appears equally vital for the device efficiency. However, the unfavorable band-offsets of the ZnO/CdS/Cu(In, Ga)Se2 heterojunction limit the device efficiency because of the deterioration of the fill factor.

scholarly journals Intracellular coupling modulates biflagellar synchrony

2021 ◽  
Vol 18 (174) ◽  
pp. 20200660
Author(s):  
Hanliang Guo ◽  
Yi Man ◽  
Kirsty Y. Wan ◽  
Eva Kanso
Keyword(s):  
Mathematical Models ◽  
Activity Level ◽  
Live Cells ◽  
Basal Bodies ◽  
Slip Mode ◽  
Biological Parameters ◽  
Hydrodynamic Coupling ◽  
Dimensionless Ratio ◽  
The Individual

Beating flagella exhibit a variety of synchronization modes. This synchrony has long been attributed to hydrodynamic coupling between the flagella. However, recent work with flagellated algae indicates that a mechanism internal to the cell, through the contractile fibres connecting the flagella basal bodies, must be at play to actively modulate flagellar synchrony. Exactly how basal coupling mediates flagellar coordination remains unclear. Here, we examine the role of basal coupling in the synchronization of the model biflagellate Chlamydomonas reinhardtii using a series of mathematical models of decreasing levels of complexity. We report that basal coupling is sufficient to achieve inphase, antiphase and bistable synchrony, even in the absence of hydrodynamic coupling and flagellar compliance. These modes can be reached by modulating the activity level of the individual flagella or the strength of the basal coupling. We observe a slip mode when allowing for differential flagellar activity, just as in experiments with live cells. We introduce a dimensionless ratio of flagellar activity to basal coupling that is predictive of the mode of synchrony. This ratio allows us to query biological parameters which are not yet directly measurable experimentally. Our work shows a concrete route for cells to actively control the synchronization of their flagella.

scholarly journals Appearance of efficient luminescence energy transfer in doped orthovanadate nanocrystals

2017 ◽  
Vol 50 (3) ◽  
pp. 787-794 ◽  
Author(s):  
Swati Bishnoi ◽  
G. Swati ◽  
Paramjeet Singh ◽  
V. V. Jaiswal ◽  
Mukesh K. Sahu ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Band Gap ◽  
Photoluminescence Intensity ◽  
X Ray Diffraction ◽  
Synthesis Mechanism ◽  
Enhanced Photoluminescence ◽  
Nir Absorption ◽  
Decay Parameters

This paper reports the detailed synthesis mechanism and the structural, morphological and optical characterization of ultraviolet (∼311 nm) excitable samarium doped gadolinium yttrium orthovanadate, (Gd,Y)VO4:Sm3+, nanocrystals. X-ray diffraction and Rietveld refinement studies confirmed that the synthesized samples crystallize in a tetragonal structure withI41/amdspace group. The enhanced photoluminescence intensity of (Gd,Y)VO4:Sm3+compared with the existing YVO4:Sm3+phosphor clearly indicates the significant role of Gd3+ions. This has been attributed to the sensitization of the6PJenergy level of Gd3+ions by energy transfer from orthovanadate (VO43−) ions and subsequent energy trapping by Sm3+ions. The energy transfer from VO43−to Sm3+viaGd3+ions as intermediates and concentration quenching of Gd3+luminescence are discussed in detail. The optical band gap of the as-prepared nanocrystals has been estimated using UV–vis–NIR absorption spectroscopy, which reveals a slightly higher band gap (3.75 eV) for YVO4as compared to GdYVO4(3.50 eV). Furthermore, confocal microcopy, decay parameters and Commission Internationale de l'Eclairage chromatic coordinates have supplemented these studies, which established the suitability of these nanophosphors for achieving spectral conversion in silicon solar cells.

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