BCS Type Research Articles

Synthesis, structure, and physical properties of a Y–Au-Ge 1/1 Tsai-type quasicrystal approximant and Y14(Au,Ge)51 with the Gd14Ag51 structure type

Exploration of the Au–Ge rich part of the pseudo-binary section Yx(Au0.70Ge0.30)100-x (3 < x < 18) in the Y–Au-Ge system afforded the intermetallic compounds Y3(Au0.7054Ge0.2946)19-x (x ≈ 0.38) and Y14(Au0.8313Ge0.1687)51, which are new representatives of the cubic 1/1 Tsai-type approximant crystal (YbCd6 parent type, space group Im3‾.) and the hexagonal Gd14Ag51 structure type (space group P6/m), respectively. Y3(Au0.7054Ge0.2946)19-x decomposes peritectically into Y14(Au,Ge)51 phase and melt at around 700 °C. In this respect the Y–Au-Ge system deviates from the Y–Au–Si system which firstly contains a second type of 1/1 approximant crystal phase with higher Y content, Y3.25(Au,Si)18-x (x ≈ 0.11) and, secondly, adjacent at higher Y composition there is a stoichiometric and ordered tetragonal phase YAu3Si. Y3(Au,Ge)19-x and Y14(Au,Ge)51 exhibit bulk superconductivity of conventional type-II BCS type albeit with very low transition temperatures (below 1 K), which is very similar to the corresponding compounds in the Y–Au–Si system.

Theoretical study of multiband Superconductivity and Enhanced Tc in Rhenium Beryllium (ReBe22) superconductor

The superconductivity of Rhenium Beryllium in two band model is theoretically studied using a standard model Hamiltonian which contains the Bardeen, Cooper and Schriefer, BCS type pairing interaction. Green function formalism was employed to obtain expression for superconducting order parameter in the bands, the coupling parameters and the superconducting critical temperature, T C , for this ReBe22 material. Our findings indicate, the enhancement of the superconducting critical temperature with the augmentation of the electron-phonon coupling strength in the entire system. The variation of the coupling parameter in the bands is understood as the reason for introducing a temperature gap and rising of the critical temperature suggesting significant upsurge at further scrutiny.

The Study of Interplay of Singlet Superconductivity and Ferromagnetism in Superconducting HoMo6Se8

This article reports the effect of magnetic ordering and superconducting order parameter on superconducting and magnetic transition temperatures of interacting singlet superconductivity and ferromagnetism in HoMo6Se8 material. The basic superconducting parameters were calculated starting with the BCS type model Hamiltonian and using the double time temperature dependent Green function formalisms. Results showed that the superconducting critical temperature decreases with enhancement of superconducting order parameter and vice versa. This is perhaps due to the weakening of the binding energy as the temperature approaches its critical value. On the other hand, the superconducting critical temperature demonstrates attenuation with increasing magnetic order parameters . It was also observed that the enhancement of magnetic transition temperature with the increase of the magnetic order parameter demonstrates variation with the alteration of the superconducting order parameter. Moreover, the calculations revealed that there is a temperature region where both superconductivity and magnetic order coexist. Furthermore, the present theoretical analysis is broadly in agreement with existing experimental findings.

Electron-phonon correlations inducing excitonic excitations in semimetal and semiconducting materials

The influence of phonons on the low-energy excitonic excitations at zero temperature in the extended Falicov-Kimball model has been investigated. In the framework of the unrestricted Hartree-Fock approximation, a set of self-consistent equations for the excitonic condensate order parameter and a lattice distortion is derived when both electron-phonon coupling and electron-hole Coulomb interaction are treated on an equal footing. The low-energy excitation properties of the excitonic condensate are addressed in signatures of the optical conductivity and the dynamical excitonic susceptibility function. The real part of the optical conductivity is evaluated by the Kubo linear response theory and the imaginary part of the dynamical excitonic susceptibility is found by adapting the random phase approximation. In the semimetal state, one always finds a sharp peak in the optical conductivity spectrum indicating the stability of the excitonic condensation in the BCS type if the correlation between electrons and phonons becomes significant. In contrast, the peak is smeared out on the semiconducting side indicating the stability of the BEC-type excitonic condensate. In this semiconducting side, the sharp peak signature appears and the system turns to the BCS-type excitonic condensation state by increasing the electron-phonon correlations. In either the semimetal or the semiconducting normal state, increasing the electron-phonon correlations always reinforces a low-energy sharp peak in the dynamical excitonic susceptibility spectrum, indicating the existence of the tightly bound excitonic excitations before the condensation state. Specifically, on the semiconducting side, the ``halo'' phase with the preformed excitons exiting outside of the BEC-excitonic condensation state has been specified. The halo phase becomes more recognizable by raising the electron-phonon correlations.

Evaluation of Immediate Functional Loading with Single Piece Implants

Introduction: In recent years, implantology has increasingly advocated the concept of immediate loading, even with single implants. It is defined as the placement of a prosthetic restoration within 48-72 hours after implant placement. Among the other advantages of immediate loading like overall treatment reduction in timing, with function, cosmetic and psychological benefits for the patient. This case described a new surgical concept and a technique to fabricate screw-retained provisional crowns for immediate loading of free-standing single tooth implants. Hence the aim of this study is to evaluate immediate functional loading with single piece implants Materials and Methods: For rehabilitation with basal implants in sites after immediate extraction, a 2-mm twist drill, the first cortex (alveolar) was drilled and then drilling was continued till the basal cortex (nasal floor/sinus floor/lingual cortex/pterygoid bone), which was perceived as a dip. For rehabilitation with compressive screw implants in healed edentulous sites, the compression screw implants in the upper and lower jaw were inserted with the primary aim of achieving stability through compression of trabecular bone along the vertical (endosseous) axis of the implant. Frequency tables and chi square tests were used to analyze the data. Results: There were 30 patients with 76 implants present and assessed for this study. The mean age of the participants was 47.43±16.93. In the study participants, 30% of the participants had hypertension, 20% had diabetes mellitus and 20% had smoking habit. BCS and Compressive type of implants were both used in the study. In 51.32% sites, BCS implants were used and 48.68% sites Compressive type implants were used depending on the clinical situation. For the success of the implant, many criteria was assessed such as Implant stability quotient, mid-buccal gingival level and inter proximal gingival papilla, absence of complications (pain, discomfort, infection, bone loss and mobility). Results showed that there was a significant association found between diabetes mellitus with mobility, bone loss and discomfort. Contrastingly there was no association between smoking habit and any of the complications affecting the success of the implant. This showed that systemic disease plays a major role in the success of the implants. Conclusion: The high cumulative implant survival rate for the devices and the technology of the Strategic Implant® indicates (within the limitations of this study) that the immediate functional loading concept with cortically anchored implants or implants providing corticalization of spongious bone for the rehabilitation of partially edentulous segments and for single-tooth replacement in maxilla and mandible can be a viable concept even in cases where extractions of teeth were done simultaneously. Keywords: Single implants, immediate loading, Compressive implants, implants, BCS implants.

Study of effective de-Gennes factor and effect of doping on superconductivity in rare-earth nickel borocarbide superconductors

We theoretically study the effective de Gennes factor and effect of doping on the critical temperature in RNi2B2C (R = Ho). We formulate a mean-field Hamiltonian model where a BCS type of Cooper pair mechanism is considered. We self-consistently solve SC order parameter, AFM order parameter and dopant concentration. The de Gennes scaling on critical temperature and Neel temperature for different Nickel borocarbide compounds gives an idea about the competition between superconductivity and antiferromagnetism in rare earth quaternary borocarbide superconductors RNi2B2C. We study here the effect of doping on the parent borocarbide superconductor HoNi2B2C. We plot the effective de-Gennes factor vs. SC critical temperature for the pseudo quaternary borocarbide compound HoxLa1-xNi2B2C for different dopant concentrations which agrees well with experimental findings.

Fully gapped superconductivity in centrosymmetric and noncentrosymmetric Re-B compounds probed with μSR

We present a comprehensive study on superconducting properties of Re$_7$B$_3$ and Re$_3$B through specific heat, magnetic susceptibility, resistivity, and transverse and zero-field muon spin rotation/relaxation ($\mu$SR) experiments on polycrystalline samples. Re$_7$B$_3$ (T$_C$ = 3.2~K) is a non-centrosymmetric type-II ($\kappa$ $\approx$ 9.27) superconductor in the weak coupling ($\lambda_{e-ph}$ = 0.54) regime. On the other hand, Re$_3$B (T$_C$ = 5.19~K) is a centrosymmetric type-II ($\kappa$ $\approx$ 34.55) superconductor in the moderate coupling ($\lambda_{e-ph}$ = 0.64) regime. Our transverse-field $\mu$SR measurements show evidence for isotropically gapped BCS type superconductivity with normalized gap ($\Delta_0/k_BT_C$) values of 1.69 (Re$_7$B$_3$) and 1.75 (Re$_3$B).

Superconductivity at 1 K in Y-Au-Si quasicrystal approximants

We report the structural and physical properties of two Y-Au-Si (YAS) compounds, ${\mathrm{Y}}_{14.1}{\mathrm{Au}}_{69.2}{\mathrm{Si}}_{16.7}$ and ${\mathrm{Y}}_{15.4}{\mathrm{Au}}_{68.6}{\mathrm{Si}}_{16.1}$, which are 1/1 approximant crystals of a Tsai-type quasicrystal without intrinsic magnetic moments. The compounds differ by the presence of either a tetrahedron (Au,Si)${}_{4}$ or a single Y atom at the center of their characteristic structural building unit consisting of concentric polyhedral shells. Both compounds exhibit bulk superconductivity, which seems to be of a conventional type-II BCS type. The compound with Y atoms at the cluster center has a slightly higher transition temperature with a sharper step in the specific heat than the compound with tetrahedral units. We discuss the occurrence of this superconducting state in the light of the specific structural and physical properties of these quasicrystal approximants.

Microscopic Study of Two Band Superconductivity in Magnesium Diboride Superconductor (MgB&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;)

We formulate a Model Hamiltonian of two band superconductivity for Magnesium Diboride superconductors (MgB₂). It is a conventional BCS type metallic superconductor which has the highest critical temperature T_c=39K. It is assumed that the superconductivity in MgB₂ arises due to metallic nature of the 2D sheets. From band structure calculations, it is observed that two types of bands i.e. σ and π bands are located at Fermi surface. Here, we consider phonon mediated superconductivity in which σ band is dominant over π band i.e. σ band is more coupled to a superconductor with much higher coupling. We consider a model Hamiltonian with mean field approach and solve this by calculating equations of motion of Green functions for a single particle. We determine the quasi-particle energy from the poles of the Green functions. We derive the single particle correlation functions and determine the two SC order parameters for both σ and π band. Here, the two SC order parameters for the bands are solved self- consistently and numerically. The conduction bandwidth (W) is considered as W=8t₀, where t₀ is the hopping integral. To make all the physical quantities dimensionless, we divide 2t₀ in each of the physical quantities. We then calculate the gap ratio 2∆(0)/K<SUB>B</SUB>T_c for both the bands. It is seen form our theoretical model that the two bands of MgB₂ superconductors have two different SC gaps with the same critical temperature. We also observe the variation of dispersion curves of quasi-particles for different temperature parameters for both σ and π band.

Solubility Enhancement of Methotrexate by Solid Nanodispersion Approach for the Improved Treatment of Small Cell Lung Carcinoma.

The present work aimed to develop MT loaded solid Nano dispersion by improving its solubility, half-life and bioavailability in biological system thereby this formulation may be afforded economically. Small cell lung carcinoma is a type of malignant tumor characterized by uncontrolled cell growth at lung tissues. The potent anti-cancer drug methotrexate (MT) chosen for the present work is poorly soluble in water (BCS type IV class) with short half-life and hepatotoxic effect. With the concept of polymeric surfactant to improve the solubility along with wettability of drugs, the present work has been hypothesized to improve its solubility using polyvinyl pyrollidone (PVP K30) polymer and α- tocopheryl polyethylene glycol 1000 succinate (TPGS) surfactant, thereby the bioavailability is expected to get enhanced. By varying the PVP K30 and TPGS ratios different formulations were developed using emulsification process. The developed MT loaded solid nanodispersion was further characterized for its particle size, charge, morphology, encapsulation efficiency and in-vitro release behavior etc. Results: The results of FT-IR spectrometric analysis indicated the compatibility nature of MTX, PVPK30 and TPGS. The developed formulations showed spherical morphology, particle size ranging from 59.28±24.2 nm to 169.33±10.85 nm with a surface charge ranging from -10.33 ± 2.81mV to -9.57 ± 1.2 mV. The in vitro release studies as performed by dialysis bag method showed a sustained release pattern as checked by UV Spectrophotometer. Residual solvent analysis for MTXNDs performed by HPLC indicates there is no residual DMSO in the formulation. Transmission electron microscopic image of MTXNDs revealed that the particles are spherical shaped with a solid core structure. Haemolytic assay indicates that the developed formulation is safe for intravenous administration. Cell culture studies in A549 cells indicates the enhanced cytotoxic effect for the developed formulation. This proof of study indicates that the developed formulation may have anticancer potential for SCLC treatment.

Collective modes and terahertz near-field response of superconductors

We theoretically study the low energy electromagnetic response of BCS type superconductors focusing on propagating collective modes that are observable with THz near field optics. The interesting frequency and momentum range is $\omega < 2\Delta$ and $q < 1/\xi$ where $\Delta$ is the gap and $\xi$ is the coherence length. We show that it is possible to observe the superfluid plasmons, amplitude (Higgs) modes, Bardasis-Schrieffer modes and Carlson-Goldman modes using THz near field technique, although none of these modes couple linearly to far field radiation. Coupling of THz near field radiation to the amplitude mode requires particle-hole symmetry breaking while coupling to the Bardasis-Schrieffer mode does not and is typically stronger. For parameters appropriate to layered superconductors of current interest, the Carlson-Goldman mode appears in the near field reflection coefficient as a weak feature in the sub-THz frequency range. In a system of two superconducting layers with nanometer scale separation, an acoustic phase mode appears as the antisymmetric density fluctuation mode of the system. This mode produces well defined resonance peaks in the near-field THz response and has strong anticrossings with the Bardasis-Schrieffer and amplitude modes, enhancing their response. In a slab consisting of many layers of quasi-two dimensional superconductors, realized for example in samples of high T$_c$ cuprate compounds, many branches of propagating Josephson plasmon modes are found to couple to the THz near field radiation.

Dipole oscillations of fermionic quantum gases along the BEC-BCS crossover in disordered potentials

We investigate dipole oscillations of ultracold Fermi gases along the BEC-BCS crossover through disordered potentials. We observe a disorder-induced damping of oscillations as well as a change of the fundamental Kohn-mode frequency. The measurement results are compared to numerical density matrix renormalization group calculations as well as to a three-dimensional simulation of non-interacting fermions. Experimentally, we find a disorder-dependent damping, which grows approximately with the second power of the disorder strength. Moreover, we observe experimentally a change of oscillation frequency which deviates from the expected behavior of a damped harmonic oscillator on a percent level. While this behavior is qualitatively expected from the theoretical models used, quantitatively the experimental observations show a significantly stronger effect than predicted by theory. Furthermore, while the frequency shift seems to scale differently with interaction strength in the BEC versus BCS regime, the damping coefficient apparently decreases with the strength of interaction, but not with the sign, which changes for BEC and BCS type Fermi gases. This is surprising, as the dominant damping mechanisms are expected to be different in the two regimes.

In-Cage Interactions in the Clathrate Superconductor Sr8 Si46.

The clathrate I superconductor Sr8Si46 is obtained under high‐pressure high‐temperature conditions, at 5 GPa and temperatures in the range of 1273 to 1373 K. At ambient pressure, the compound decomposes upon heating at T=796(5) K into Si and SrSi2. The crystal structure of the clathrate is isotypic to that of Na8Si46. Chemical bonding analysis reveals conventional covalent bonding within the silicon network as well as additional multi‐atomic interactions between Sr and Si within the framework cages. Physical measurements indicate a bulk BCS type II superconducting state below T c=3.8(3) K.

Superconductivity of Y5Rh6Sn18; Coexistence of the high temperature thermal lattice relaxation process and superconductivity

The heat capacity, magnetic, and electrical transport properties of skutterudite-related Y5Rh6Sn18 compound indicate intriguing coexistence of the high temperature thermal lattice relaxation process at temperatures higher than 350 K and superconductivity below the superconducting transition temperature Tc=3.08 K. Y5Rh6Sn18, having a cage-like structure crystallises in tetragonal structure with the space group I41/acd. The gap structure of this compound is found not to be characteristic of conventional BCS type superconductors. Anomalous behaviour observed in the electronic specific heat C(T)/T and the upper critical field Hc2(T) data may suggest the presence of two superconducting gaps in this compound. The ab initio band structure calculations showed a significant contribution of s and p Sn states as well as Rh and Y d-electron states to the total density of states near the Fermi level, which supports the multi-band superconductivity of this compound. Several electronic quantities and parameters characterising the superconducting and normal state of Y5Rh6Sn18 are calculated within the Ginzburg-Landau-Abrikosov-Gorkov theory. The data reveals dirty limit superconductivity in Y5Rh6Sn18 superconductor of type-II.

Effect of Next-Nearest-Neighbor Electron Hopping on Superconducting Gap of Cuprate Superconductors

We study here a single band Hamiltonian model to describe the effect of next-nearest-neighbor (NNN) electron hopping on superconducting gap in Cuprates. The Hamiltonian consists of nearest-neighbor (NN) and next-nearest-neighbor (NNN) electron hopping integrals between the copper sides. By taking d-wave pairing symmetry into account, BCS type superconducting interaction is studied. By applying Zubarev’s Green function technique, the total Hamiltonian is solved. From the correlation function, the temperature-dependent superconducting gap (SC) equation is derived and is computed self-consistently by using technique [Formula: see text] grid points of the electron momentum. By varying SC coupling, chemical potential, J-T coupling parameter and second-nearest-neighbor electron hopping integral, the evolution of the order parameter is investigated.

Novel scheme for rapid synthesis of hollow mesoporous silica nanoparticles (HMSNs) and their application as an efficient delivery carrier for oral bioavailability improvement of poorly water-soluble BCS type II drugs.

Hollow mesoporous silica nanoparticles (HMSNs) are one of the most promising carriers for drug delivery. However, a facile method to synthesize HMSNs has hardly been reported so far. The primary objective of our current study was to develop HMSNs using a simple, quick, and inexpensive method and evaluate their ability to enhance solubility, dissolution rate, and bioavailability of poorly water-soluble model BSC type II drug Carvedilol. Traditional mesoporous silica nanoparticles (MSNs) are synthesized using classical Stober method and HMSNs with an entire hollow core was induced by immersing cetyltrimethylammonium bromide (CTAB) in hot water. Initial MSNs were added in boiling distilled water to synthesize hollow structure, to enhance pore size, and also to remove CTAB template. HMSNs prepared in our current study has exhibited high surface area (886.84 m2/g), pore volume (0.79 cm3/g), and uniform pore size (3.18 nm), which also enabled the greater encapsulation of the model BSC II drug Carvedilol (CAR) inside the HMSNs. This technique also helped in achieving a high drug loading of (40.22 ± 0.73)%. Add to all this, in vitro studies conducted in the present work showed that compared with pure CAR and CAR loaded MSNs (CAR-MSNs) synthesized by Stober method, the drug-loaded HMSNs (CAR-HMSNs) exhibit sustained drug release performance. The high drug loading and sustained release can be attributed to the hollow porous structure of the HMSNs. Finally, a pharmacokinetic analysis in rats indicated a significant increase in bioavailability of carvedilol HMSNs in vivo compared to the pure carvedilol and carvedilol loaded MSNs. This study, therefore, offered a new, simple, and quick method to develop HMSNs with the ability to support higher loading and controlled release behavior in vitro and enhanced absorption of poorly-aqueous soluble drugs in-vivo.

Microscopic study of the role of second nearest neighbour spin density wave coupling and electron hopping on superconducting gap

We report here a tight binding single band model Hamiltonian to study the role of spin density wave interaction and superconductivity. The Hamiltonian consists of nearest and next nearest neighbour electron hopping between the copper sides. The spin density wave interaction also includes nearest-neighbour and the next-nearest-neighbour spin interactions within a mean field approximation. BCS type superconducting interaction is considered taking d-wave pairing symmetry. By using Zubarev's Green function technique the Hamiltonian is solved. The antiferromagnetic and the superconducting gap equations are derived from the correlation functions and are solved self-consistently technique 100 × 100 grid points of the electron momentum. The evolution of these two order parameters are investigated by varying hole doping concentration, superconducting coupling, spin density wave coupling and second nearest neighbour electron hopping integrals.

Microscopic study of the role of second nearest neighbour spin density wave coupling and electron hopping on superconducting gap

We report here a tight binding single band model Hamiltonian to study the role of spin density wave interaction and superconductivity. The Hamiltonian consists of nearest and next nearest neighbour electron hopping between the copper sides. The spin density wave interaction also includes nearest-neighbour and the next-nearest-neighbour spin interactions within a mean field approximation. BCS type superconducting interaction is considered taking d-wave pairing symmetry. By using Zubarev's Green function technique the Hamiltonian is solved. The antiferromagnetic and the superconducting gap equations are derived from the correlation functions and are solved self-consistently technique 100 × 100 grid points of the electron momentum. The evolution of these two order parameters are investigated by varying hole doping concentration, superconducting coupling, spin density wave coupling and second nearest neighbour electron hopping integrals.

Preparation of Fenofibrate loaded Eudragit L100 nanoparticles by nanoprecipitation method

Abstract Successful adsorption of oral administered drugs is hindered by degradation during first pass metabolism. One method that has been recently employed to increase bioavailability of drugs is to encapsulate them in polymeric nanoparticles. In this study, Fenofibrate, used as a model substance for BCS type II drugs, has been encapsulated in Eudragit L100 nanoparticles, which shows pH dependent solubility at pH >6, thus release characteristics. This enables the loaded NPs to pass through the stomach without degradation until it reaches the intestine, where the drug is released and absorbed. For encapsulation, solvent displacement method was employed. Parameters that affect NPs quality such as polymer concentration, surfactant presence and concentration, and organic and aqueous ratio were optimized. In addition, an encapsulation efficiency test was carried out. The optimized concentration for Eudragit L100 was 1.35% since it was enough to get a critical nucleation concentration but not too high so that agglomeration is propitiated. Moreover, the surfactant with the best stabilization capacity was Tween® 80 due to its non-polymeric nature with a critical concentration obtained at 0.25%. Finally, a formulation with an end concentration of 250 µg/mL, presented the highest %EE determined with an HPLC assay.

The σ-phase superconductors Nb20.4Rh5.7Ge3.9 and Nb20.4Rh5.7Si3.9

We show that the previously unreported ternary σ phases Nb20.4Rh5.7Ge3.9 and Nb20.4Rh5.7Si3.9 are both superconductors with Tc values of approximately 1.9 K. The superconducting transitions were characterized through temperature-dependent magnetic susceptibility, electrical resistance, and specific heat measurements. The Sommerfeld constants, γ, for Nb20.4Rh5.7Ge3.9 and Nb20.4Rh5.7Si3.9 are 89(1) mJ mol-f.u.−1K−2 and 86(1) mJ mol-f.u.−1K−2 (about 3.0 and 2.9 mJ mol-atom−1 K−2), respectively. The normalized specific heat jumps at Tc, ΔC/γTc, are approximately 1.39 for Nb20.4Rh5.7Ge3.9 and 1.30 for Nb20.4Rh5.7Si3.9, consistent with both materials being weakly coupled BCS type superconductors.