BCS Type Research Articles

Superconducting tantalum nitride-based normal metal-insulator-superconductor tunnel junctions

We report the development of superconducting tantalum nitride (TaNx) normal metal-insulator-superconductor (NIS) tunnel junctions. For the insulating barrier, we used both AlOx and TaOx (Cu-AlOx-Al-TaNx and Cu-TaOx-TaNx), with both devices exhibiting temperature dependent current-voltage characteristics which follow the simple one-particle tunneling model. The superconducting gap follows a BCS type temperature dependence, rendering these devices suitable for sensitive thermometry and bolometry from the superconducting transition temperature TC of the TaNx film at ∼5 K down to ∼0.5 K. Numerical simulations were also performed to predict how junction parameters should be tuned to achieve electronic cooling at temperatures above 1 K.

The Coexistence of Super Conductivity and Spin Density Wave (SDW) in SmO<sub>1-x</sub>F<sub>x</sub>FeAs

The coexistence of superconductivity and spin density wave in SmO1-xFxFeAs is theoretically studied using the model Hamiltonian which contains BCS type superconductivity and spin density wave terms. Employing green function formalism, the expression for the spin density wave order parameter (M) and expression for spin density wave transition temperature TSDW is obtained. The interplay between the superconductivity and spin density wave is examined in these parameters and the coexistence of the two states is established in the order parameter range of 0.1≤MmeV≤0.13 which is seen to be in broad experimental agreement.

EFFECTS OF DEFECTS AND ANHARMONICITY ON dx2-y2 WAVE PAIRING SYMMETRY IN CUPRATES

In this paper, the renormalized frequency spectrum and one-particle spectral function of a high temperature superconductor (HTS) is studied using double time thermodynamic Green's function approach via a newly formulated Hamiltonian (without considering BCS type Hamiltonian) which includes the effects of electron–phonon interactions, anharmonicities and that of isotopic impurities. It is investigated that the renormalized frequency further invokes the appearance of energy gap and functional dependence of dx2-y2 wave pairing in the superconducting state in cuprates. The salient feature of the present theory is the electron–phonon interaction in the vicinity of the impurity atoms reveals four-fold symmetric quasiparticle "cloud" aligned with the nodes of d-wave superconducting gap, which is believed to characterize superconductivity in high temperature superconducting materials. It has been further inferred that, a modest contribution of anharmonicity can also induce superconductivity.

Use of the FoundationOne next-generation sequencing (NGS) assay to detect actionable alterations leading to clinical benefit of targeted therapies for relapsed and refractory breast cancer.

1009 Background: Genomically-informed cancer therapy linking therapeutics targeting the molecular alterations driving the malignancy has the potential to transform the care of patients with metastatic breast cancer (MBC). Methods: DNA was isolated from 4 FFPE sections cut at 10 microns from 177 consecutive MBC that had relapsed after surgery, conventional hormonal/chemo and anti-HER2 targeted therapies received by our CLIA lab (Foundation Medicine). DNA sequencing was performed for 3,320 exons of 182 cancer-related genes to average depth of 1017X. Actionable Genomic alterations (GA) were defined as those linked to targeted anti-cancer therapies approved or being evaluated in active registered clinical trials. Results: Genomic profiles were generated from 169/177 (95%) BCs identifying 565 GA, averaging 3.34 GAs per tumor (range 0 to 10). 152 (90%) tumors harbored an actionable alteration mean 1.88 per tumor (range 0 to 6). In 124 (73%) tumors, ≥1.0 actionable GA was detected that would be missed by current “hotspot assays”. Notable GA involved PIK3CA (37%), ERBB2 (14%), FGFR1/2 (14%), PTEN (10%), MDM2 (7%), CCND1/CCNE1/CDK4 (7%), BRCA1 and BRCA2 (6% each) and ESR1 and EGFR (3% each). Of 23 ERBB2 GA, 74% were amplifications and 26% were mutation/gene fusion. The frequency of ERBB2 mutation/fusion was significantly enriched in CDH1 mutated ILC (~9% of total BC) with a frequency of 19.0% (4/21) compared to other histological types of BCs 1.4% (2/148) [p=0.002]. Significant clinical efficacy included patients with HER2 IHC/FISH negative tumors featuring HER2 and EGFR activating mutations benefitting from lapatinib/trastuzumab and erlotinib respectively. Conclusions: Comprehensive genomic profiling with a NGS assay identified actionable GAs in the majority of MBC patients including ERBB2 and EGFR mutations that initiated use of targeted therapies resulting in significant clinical benefit. These data provide a framework for the GAs expected in advanced BC and should facilitate the implementation of molecularly targeted trials supporting the efforts for a modern approach to precision medicine for the disease.

A semi-microscopic approach to the backbending phenomena in even-even nuclei

The phenomenon of backbending in rare earth nuclei is described by means of the band hybridization mechanism. The hybridization of two rotational bands is performed by treating a model Hamiltonian associated with a set of interacting particles moving in a deformed mean field and coupled to a phenomenological core described in terms of quadrupole boson operators, in a product space of angular momentum projected states. The model states for the ground and S bands are obtained by angular momentum projection of a deformed product state with an axially symmetric coherent boson state standing for the core factor function and a BCS type single-particle factor function defining the nature of the band. The yrast band energies are defined by the lowest eigenvalues of the model Hamiltonian in an orthogonal basis constructed by diagonalizing the overlap matrix of the ground and S band states, which are not mutually orthogonal. The formalism is positively tested on six deformed even-even nuclei known to exhibit a backbending behavior in their moment of inertia.

Renormalization effects and phonon density of states in high temperature superconductors

Using the versatile double time thermodynamic Green's function approach based on many body theory the renormalized frequencies, phonon energy line widths, shifts and phonon density of states (PDOS) are investigated via a newly formulated Hamiltonian (does not include BCS type Hamiltonian) that includes the effects of electron-phonon, anharmonicities and that of isotopic impurities. The automatic appearance of pairons, temperature, impurity and electron-phonon coupling of renormalized frequencies, widths, shifts and PDOS emerges as a characteristic feature of present theory. The numerical investigations on PDOS for the YBa2Cu3O7 − δ crystal predicts several new feature of high temperature superconductors (HTS) and agreements with experimental observations.

Crossover between BCS Superconductor and Doped Mott Insulator ofd-Wave Pairing State in Two-Dimensional Hubbard Model

With high-Tc cuprates in mind, properties of correlated dx2-y2-wave superconducting (SC) and antiferromagnetic (AF) states are studied for the Hubbard (t-t'-U) model on square lattices, using a variational Monte Carlo method. We employ simple trial wave functions including only crucial parameters, such as a doublon-holon binding factor indispensable to describe correlated SC and normal states as doped Mott insulators. U/t, t'/t and \delta (doping rate) dependence of relevant quantities are systematically calculated. As U/t increases, a sharp crossover of SC properties occurs at U_co/t \sim 10 from a conventional BCS type to a kinetic-energy-driven type for any t'/t. As \delta decreases, U_co/t is smoothly connected to the Mott transition point at half filling. For U/t\lsim 5, steady superconductivity corresponding to the cuprates is not found, whereas the d-wave SC correlation function Pd^\infty rapidly increases for U/t\gsim 6 and becomes maximum at U=U_co. Comparing the \delta dependence of Pd^\infty with experimentally observed dome-shaped Tc and condensation energy, we find that the effective value of $U$ for the cuprates should be larger than the band width, for which the t-J model is valid. Analyzing the kinetic energy, we reveal that for U>U_co only doped holes (electrons) become charge carriers, which will make a small Fermi surface (hole pocket), but for U<U_co all the electrons (holes) contribute to conduction and will make an ordinary large Fermi surface, which is contradictory to the feature of cuprates. By introducing a proper negative (positive) t'/t, the SC (AF) state is stabilized. In the underdoped regime, the strength of SC for U>U_co is determined by two factors, i.e., the AF spin correlation, which creates singlet pairs (pseudogap), and the charge mobility dominated by Mott physics.

Coexistence of Superconductivity and Antiferromagnetism and its Effects on Crossover as to Correlation Strength in Hubbard Model

Abstract Using a variational Monte Carlo method, the interplay between antiferromagnetism and superconductivity is studied for the two- dimensional Hubbard model with a diagonal transfer t’. It is found with a refined function that the optimized state is sensitive to the values of model parameters, U/t, t’/t, and δ (doping rate), and becomes a coexisting state or a pure superconducting (SC) state. SC properties in the coexisting state also undergo considerable changes around the crossover point Uco(~10t) from a fragile BCS type for U Uco, in which pairs are formed through local exchange or doublon-holon processes, but supercurrent flows separately with the doped holes.

Mechanistic investigation of food effect on disintegration and dissolution of BCS class III compound solid formulations: the importance of viscosity

A negative food effect, i.e. a decrease in bioavailability upon the co-administration of compounds together with food, has been attributed particularly with high solubility/low permeability compounds (BCS class III). Different mechanisms have been proposed including intestinal dilution leading to a lower concentration gradient across the intestinal wall as well as binding of the active pharmaceutical ingredient to food components in the intestine and thereby decreasing the fraction of the dose available for absorption. These mechanisms refer primarily to the compound and not to the dosage form. An increase in viscosity of the dissolution fluid will in particular affect the absorption of BCS type III compounds with preferential absorption in the upper small intestine if the API release is delayed from the dosage form. The present study demonstrated that the increase in viscosity of the dissolution medium, following ingestion of a solid meal, may drastically reduce disintegration and dissolution. For that purpose the viscosity of the standard FDA meal was determined and simulated by solutions of HPMC in buffer. As model formulations, three commercially available tablets containing trospium chloride, a BCS class III m-cholinoreceptor antagonist was used. Trospium chloride drug products have been described to undergo a negative food effect of more than 80% following ingestion with food. The tablets showed prolonged disintegration times and reduced dissolution rates in viscous media, which could be attributed to changes in the liquid penetration rates. The effect was particularly significant for film-coated tablets relative to uncoated dosage forms. The results show the necessity of considering media viscosity when designing in vitro models of drug release for BCS type III drug formulations.

Variational Monte Carlo Study of Spin-Gapped Normal State and BCS–BEC Crossover in Two-Dimensional Attractive Hubbard Model

We study properties of normal, superconducting (SC) and CDW states for an attractive Hubbard model on the square lattice, using a variational Monte Carlo method. In trial wave functions, we introduce an interspinon binding factor, indispensable to induce a spin-gap transition in the normal state, in addition to the onsite attractive and intersite repulsive factors. It is found that, in the normal state, as the interaction strength $|U|/t$ increases, a first-order spin-gap transition arises at $|U_{\rm c}|\sim W$ ($W$: band width) from a Fermi liquid to a spin-gapped state, which is conductive through hopping of doublons. In the SC state, we confirm by analysis of various quantities that the mechanism of superconductivity undergoes a smooth crossover at around $|U_{\ma{co}}|\sim |U_{\rm c}|$ from a BCS type to a Bose-Einstein condensation (BEC) type, as $|U|/t$ increases. For $|U|<|U_{\ma{co}}|$, quantities such as the condensation energy, a SC correlation function and the condensate fraction of onsite pairs exhibit behavior of $\sim \exp(-t/|U|)$, as expected from the BCS theory. For $|U|>|U_{\ma{co}}|$, quantities such as the energy gain in the SC transition and superfluid stiffness, which is related to the cost of phase coherence, behave as $\sim t^2/|U|\propto T_{\rm c}$, as expected in a bosonic scheme. In this regime, the SC transition is induced by a gain in kinetic energy, in contrast with the BCS theory. We refer to the relevance to the pseudogap in cuprate superconductors.

Dynamic Jahn–Teller effect in the parent insulating state of the molecular superconductor Cs3C60

The 'expanded fulleride' Cs(3)C(60) is an antiferromagnetic insulator in its normal state and becomes a molecular superconductor with T(c) as high as 38 K under pressure. There is mounting evidence that superconductivity is not of the conventional BCS type and electron-electron interactions are essential for its explanation. Here we present evidence for the dynamic Jahn-Teller effect as the source of the dramatic change in electronic structure occurring during the transition from the metallic to the localized state. We apply infrared spectroscopy, which can detect subtle changes in the shape of the C(60)3- ion due to the Jahn-Teller distortion. The temperature dependence of the spectra in the insulating phase can be explained by the gradual transformation from two temperature-dependent solid-state conformers to a single one, typical and unique for Jahn-Teller systems. These results unequivocally establish the relevance of the dynamic Jahn-Teller effect to overcoming Hund's rule and forming a low-spin state, leading to a magnetic Mott-Jahn-Teller insulator.

Spin-gapped wave function as normal state in attractive Hubbard model

With the pseudogap in cuprate superconductors in mind, we study an attractive Hubbard model on the square lattice, in which the mechanism of superconductivity undergoes a crossover at | U co|/ t from a BCS type to a Bose-Einstein condensation type, as the interaction strength | U |/ t increases. Correspondingly, for | U |>| U co|, a normatate, realized for T > T c, is considered to exhibit gapped behavior. We try to construct such a state and study its properties using a variational Monte Carlo method, which treats the local correlation accurately and can connect the weak-and strong-correlation limits continuously. We introduce an intersite correlation factor between antiparallel spins in nearest-neighbor sites, in addition to the onsite (Gutzwiller) projection. This factor brings about a first-order transition from a metal to a spin-gapped phase at | U= | U c |= W (bandwidth). For | U |>| U c|, a gap opens in the spin degree of freedom, whereas the charge sector remains gapless. In this phase, conductivity is caused by a hopping of doublons.

Theory of Electron Density of States of High Temperature Impurity Induced Anharmonic Superconductors

The expression for the electron density of states (EDOS) of high temperature superconductors (HTS) has been derived taking the disorder and anharmonicity effects as a central problem. This has been dealt with the help of double time thermodynamic Green’s function theory for electrons via a generalized Hamiltonian which consists of the contribution due to 1) unperturbed electrons; 2) unperturbed phonons; 3) isotopic impurities; 4) anharmonicities (no BCS type Hamiltonian has been taken up in the formulation); and 5) electron-phonon interactions. The renormalization effects and emergence of pairons appears as a unique feature of the theory and dependence of EDOS on impurity concentration and temperature has been discussed in details with special reference to the HTS.

Self-consistent pairing interaction and collective motion in nuclei: a semiclassical approach

The solutions of the semiclassical time–dependent Hartree–Fock-Bogoliubov equations of motion are studied in a linear approximation in which the pairing field is allowed to oscillate and to become complex. The pairing field fluctuations are derived from the self–consistent relation (the gap equation of the BCS type), while the static pairing field is approximated with a phenomenological constant Δ. The self–consistent pairing-field fluctuations introduce possibility of new collective modes of the system. We have found out the dispersion relation which determines possible collective modes of the system generated by the pairing interaction. The obvious solution of our dispersion relation at ω=0 corresponds to the Anderson–Goldstone–Nambu mode and is related to gauge symmetry. The solutions of dispersion relation have been studied in a simple model, in which nuclei are represented as homogeneous spheres of symmetric nuclear matter characterized by parameters (size, density, pairing gap) typical of heavy nuclei. We have found that the dispersion relation has approximate solution at ħω≈2Δ for the monopole channel. Our semiclassical approach is valid for both weak and strong pairing. Here we focus on weak pairing which is suitable for systems with size and pairing parameter appropriated to nuclei.

Novel approach for detection of isolated tumor cells in pulmonary vein using negative selection method: morphological classification and clinical implications☆☆☆

The presence of isolated tumor cells (ITCs) in the pulmonary vein (PV) of a lung resected for lung cancer has been reported to be a prognostic factor. Previous investigations noted correlations between prognosis and the presence or amount of ITCs, although few studies have investigated the clinical implications of the morphological characteristics of those cells. We assessed the clinical implications of ITCs in the PV using a novel enrichment approach that maintained their morphological characteristics. Ninety-four consecutive patients with primary non-small-cell lung cancer (NSCLC) without preoperative chemo- and/or radiation therapy (p-stage I in 75, II in 13, III or IV in six) were studied. Blood samples were drawn from the PV draining the lung just after pulmonary resection, and ITCs were enriched using a CD45-negative selection method and density-gradient centrifugation, followed by Papanicolaou staining using 1ml of PV blood and immunohistochemical staining for cytokeratin in cases with an additional available blood sample. The ITCs were classified into four types based on patterns of cluster formation: no tumor cells (N), singular tumor cells (S), clustered cells (≤ 0.2mm) (CSs), and bulky clustered cells (> 0.2mm) (BCSs). We evaluated the correlations between ITC morphology and clinical results. ITCs were detected in 68 of 94 patients (72%), of which the BCS type was observed in two, CS in 33, S in 33, and N in 26. Over a median follow-up period of 13 months (range 6-22 months), cancer recurrence occurred in 16 cases (17%): 14 in the combined CS/BCS group, one in S, and one in N. Log-rank analysis revealed that the disease-free survival rate was exclusively worse in patients with clustered ITCs as compared with the other two groups (p < 0.01). The present method was useful to detect and enrich ITCs from the PV, and showed the clinical relevance of their morphology in lung cancer cases. The presence of ITC clusters may be a prognostic biomarker for patients with resected NSCLC.

Reply to “Comment on `Isotope Effect in Multi-Band and Multi-Channel Attractive Systems and Inverse Isotope Effect in Iron-Based Superconductors”'

The Comment insists on the following: in our model it is assumed that the effective interactions have specific energy ranges within the single band with a cutoff at \omega_1 for the phononic part and a range from \omega_1 to \omega_2 in the AF channel. Our reply is that we assume that V_i(k,k')\neq 0 if |\xi_k|<\omega_i and |\xi_{k'}|<\omega_i, and otherwise V_i(k,k')= 0 (i=1,2), as stated in our paper. This is the model of BCS type with two attractive interactions, and this assumption is the characteristic of the BCS approximation. The claim "the integration limits have been modified such that the AF channel mediated pairing sets in where the ph-channel pairing terminates and is limited at an energy given by \omega_j=\omega_{AF}" in the Comment is wrong. We describe the model and the method to solve the gap equation in more detail.

Development of biodegradable porous starch foam for improving oral delivery of poorly water soluble drugs

A biodegradable porous starch foam (BPSF) was developed for the first time as a carrier in order to improve the dissolution and enhance the oral bioavailability of lovastatin – defined as a model poorly water soluble BCS type II drug. In this paper, BPSF was prepared by the solvent exchange method and characterized by scanning electron microscopy (SEM) and nitrogen adsorption/desorption analysis in order to perform the morphological and structural characterization of BPSF. Lovastatin was loaded by immersion/solvent evaporation into the BPSF which provided a stable hydrophilic matrix with a nano-porous structure. The solid state properties of the loaded BPSF samples were characterized by SEM, Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC). In vitro and in vivo drug release studies showed that when BPSF was used as a carrier it allowed immediate release of lovastatin and enhanced the dissolution rate in comparison with crystalline lovastatin and commercial capsules. These results provide important information about the mechanism of drug adsorption and release from BPSF as a carrier. Accordingly, BPSF has a promising future as a device for the oral delivery of poorly water soluble drugs.

Interplay of superconductivity and magnetism in presence of inter sub-lattice effect in cuprates

In the present communication, we report a model Hamiltonian to study the interplay between the two long range orders of anti-ferromagnetism (AFM) and superconductivity (SC) in cuprate superconductors in presence of the intersite pairing effect. The BCS type but non-phonon pairing mechanism is considered among the electrons of two equivalent ‘Cu’ sites. The pairing among the electrons of two nearest neighbour non-equivalent ‘Cu’ sites is included in the Hamiltonian and its effect on the interplay of SC and AFM is investigated. The Hamiltonian is solved by the Green’s function method and the corresponding gap equations are calculated and solved selfconsistently. The influence of model parameters like AFM coupling (λ), SC couling (λ1) and the coupling (λ2) for intersite superconducting interactions on the gaps (SC and AFM) are studied numerically and the results are reported.

Density of state and effect of external magnetic field on co-existence state of SC and AFM in high- [formula omitted] cuprates

A mean field Hamiltonian model is taken for our system to study density of states and the effect of external magnetic field on superconductivity (SC) and antiferromagnetism (AFM) at the co-existence stage in high- T c cuprates. The order parameters corresponding to SC and AFM long range orders are determined. The variation of dimensionless superconducting gap ( z ) and AFM gap ( h ̃ ) with temperature are investigated at different magnetic fields. The gap parameters are found to be strongly coupled to each other through their coupling constants. The interplay displays a BCS type of two gaps in the quasi-particle density of states which resemble the tunneling conductance of the STM experiment. The two gap edges in the density of states(DOS) appear at ± ( h ̃ 2 + z ) and ± ( h ̃ 2 − z ) . The effect of external magnetic field on DOS is also studied.

Fate of the superconducting ground state on the Moyal plane

It is known that Berry curvature of the band structure of certain crystals can lead to effective noncommutativity between spatial coordinates. Using the techniques of twisted quantum field theory, we investigate the question of the formation of a paired state of twisted fermions in such a system. We find that to leading order in the noncommutativity parameter, the gap between the non-interacting ground state and the paired state is smaller compared to its commutative counterpart. This suggests that BCS type superconductivity, if present in such systems, is more fragile and easier to disrupt.