Wave Pairing Research Articles

THz optical response of Ba(Fe[formula omitted]Ni[formula omitted])[formula omitted]As[formula omitted] films analyzed within the three-band Eliashberg s[formula omitted]-wave model

The uncertainty of the nature of the normal state and superconducting condensate of unconventional superconductors continues to stimulate considerable speculation about the mechanism of superconductivity in these materials. Of particular interest are the type of symmetry of the order parameter and the basic electronic characteristics of the superconducting and normal states. We report the derivation of temperature dependences of the superconducting condensate plasma frequency, superfluid density, and London penetration depth by measuring terahertz spectra of conductivity and dielectric permittivity of the Ba(Fe1−xNix)2As2 thin films with different Ni concentrations. A comprehensive analysis of the experimental data was performed in the framework of the simple three-band Eliashberg model under the assumption that the superconducting coupling mechanism is mediated by antiferromagnetic spin fluctuations. The results of independent experiments support the choice of model parameters. Based on calculations of the temperature dependences of superconducting gaps, we may conclude that the obtained results are compatible with the scenario, in which Ba(Fe1−xNix)2As2 is a multiband superconductor with s±-wave pairing symmetry.

The Relationship between Cardiomyocyte Action Potentials and Ion Concentrations: Machine Learning Prediction Modeling and Analysis of Spontaneous Spiral Wave Generation Mechanisms

The changes in cardiomyocyte action potentials are related to variations in intra- and extracellular ion concentrations. Abnormal ion concentrations can lead to irregular action potentials, subsequently affecting wave propagation in myocardial tissue and potentially resulting in the formation of spiral waves. Therefore, timely monitoring of ion concentration changes is essential. This study presents a novel machine learning classification model that predicts ion concentration changes based on action potential variation data. We conducted simulations using a single-cell model, generating a dataset of 850 action potential variations corresponding to different ion concentration changes. The model demonstrated excellent predictive performance, achieving an accuracy of 0.988 on the test set. Additionally, the causes of spontaneous spiral wave generation in the heart are insufficiently studied. This study presents a new mechanism whereby changes in extracellular potassium ion concentration leads to the spontaneous generation of spiral waves. By constructing composite myocardial tissue containing both myocardial and fibroblast cells, we observed that variations in extracellular potassium ion concentration can either trigger or inhibit cardiomyocyte excitation. We developed three tissue structures, and by appropriately adjusting the extracellular potassium ion concentration, we observed the spontaneous generation of single spiral waves, symmetrical spiral wave pairs, and asymmetrical double spiral waves.

Sex differences in tobacco use, attempts to quit smoking, and cessation among dual users of cigarettes and e-cigarettes: Longitudinal findings from the US Population Assessment of Tobacco and Health Study

SignificanceA growing number of adults use more than one tobacco product, with dual use of cigarettes and e-cigarettes being the most common combination. Monitoring sex disparities in tobacco use is a public health priority. However, little is known regarding whether dual users differ by sex. MethodsData came from Waves 4–6 (12/2016–11/2021) of the Population Assessment of Tobacco and Health Study, a US nationally-representative longitudinal survey. This analysis included current adult dual users of cigarettes and e-cigarettes. We used weighted generalized estimating equations to assess the association between sex and (1) making a cigarette quit attempt (n = 1882 observations from n = 1526 individuals) and (2) smoking cessation (n = 2081 observations from n = 1688 individuals) across two wave pairs, adjusting for age, education, ethnicity, time-to-first cigarette after waking, and e-cigarette use frequency. ResultsAmong US dual users, 14.1% (95% Confidence Intervals [Cl] = 11.9–16.4) of females and 23.4% (20.0–26.9) of males were young adults (aged 18–24), 11.7% (9.2–14.2) of females and 14.4% (11.6–17.2) of males had <high school education, and 82.2% (79.4–84.5) of females and 78.7% (75.1–82.4) of males were white. Overall, 44.9% (41.6–48.1) of females compared with 37.4% (33.5–41.3) of males made an attempt to quit smoking between a baseline and follow-up wave (Adjusted Risk Ratio [ARR] = 1.23, 1.05–1.45). In contrast, there were no apparent differences between females (22.1%, 19.0–25.2) and males (24.3%, 21.5–27.1) in smoking cessation (ARR = 1.06, 0.84–1.35). ConclusionUS females who dually use e-cigarettes and cigarettes were more likely to attempt to quit smoking, but not more likely to succeed at quitting, than males.

High-TC superconductivity in La3Ni2O7 based on the bilayer two-orbital t-J model

The recently discovered high-Tc superconductor La3Ni2O7 has sparked renewed interest in unconventional superconductivity. Here we study superconductivity in pressurized La3Ni2O7 based on a bilayer two-orbital t−J model, using the renormalized mean-field theory. Our results reveal a robust s±-wave pairing driven by the inter-layer dz2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{z}^{2}}$$\\end{document} magnetic coupling, which exhibits a transition temperature within the same order of magnitude as the experimentally observed Tc ~ 80 K. We establish a comprehensive superconducting phase diagram in the doping plane. Notably, the La3Ni2O7 under pressure is found to be situated roughly in the optimal doping regime of the phase diagram. When the dx2−y2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{x}^{2}-{y}^{2}}$$\\end{document} orbital becomes close to half-filling, d-wave and d + is pairing can emerge from the system. We discuss the interplay between Fermi surface topology and different pairing symmetries. The stability of the s±-wave pairing against Hund’s coupling and other magnetic exchange couplings is discussed.

Personal characteristics associated with switching from Cigarettes to Non-combustible tobacco and nicotine products among U.S. adults: Findings from PATH Study Wave 1 - Wave 5.

Reducing the disease burden from tobacco smoking may encompass switching to non-combustible (NCs), along with cessation. This study evaluates factors associated with switching to NCs (e-cigarettes, smokeless, snus) versus continued smoking, complete cessation, or dual use. Population Assessment of Tobacco and Health adult data were analyzed in three two-year wave pairs across 2013-2019 to assess product transitions among people who exclusively smoked tobacco. Generalized estimating equations examined demographics, smoking characteristics, perceptions, and messaging exposure as predictors of transitions from cigarette smoking. Ages 18-44 years (ref=65+; aORs=3.79-5.92), males (aOR=1.18, 95%CI[1.01,1.37]), and perceiving NCs as less harmful than smoking (ref=not; aOR=1.47, 95%CI[1.28,1.69]) were positively associated with switching to NCs versus continued smoking, while being Black (ref=White; aOR=0.36, 95%CI[0.26,0.48]) or Hispanic (ref=Non-Hispanic; aOR=0.59, 95%CI[0.45,0.78]) were negatively associated. Ages 18-64 years (aORs=2.49-5.89), noticing promotional ads (ref=not; aOR=1.34, 95%CI[1.14,1.58]), daily light or heavy smoking (ref=nondaily; aORs=2.33-3.72), and smoking within 30 mins of waking (ref=>30min; aOR=1.47, 95%CI[1.18,1.85]) were positively associated with switching to NCs versus cessation, while being Black (aOR=0.55, 95%CI[0.38,0.74]) or Hispanic (aOR=0.52, 95%CI[0.38,0.71]) were negatively associated.. Incomes of $10,000->$100,000 (ref=<$10,000; aORs=2.08-3.13) and daily heavy smoking (aOR=1.96, 95%CI[1.11,3.48]) were positively associated with switching to NCs versus dual use, while being male (aOR=0.44, 95%CI[0.29,0.65]) was negatively associated. Transitioning to NCs was unequally distributed among sociodemographic groups and smoking characteristics. The mere availability of NCs may not promote health equity. Continued market and regulatory efforts that promote both smoking cessation and transitioning to NCs among various populations may promote public health gains. This study examines factors associated with transitioning from smoking to non-combustible tobacco product use. We examined three different product use scenarios that may be associated with varied levels of exposure to harm. We observed that younger ages and perceiving NCs as less harmful than cigarettes were more likely to transition to NCs as compared to continued smoking and cessation, while Black or Hispanic individuals were less likely to transition to NCs. This highlights the need for more focused harm reduction efforts for racial and ethnic minority populations as a complementary strategy to cessation to reduce health disparities from smoking.

About splitting of energy gap in superfluid neutron matter with spin-triplet anisotropic p-wave pairing at nuclear and supranuclear densities in superstrong magnetic fields

About splitting of energy gap in superfluid neutron matter with spin-triplet anisotropic <i>p-</i>wave pairing at nuclear and supranuclear densities in superstrong magnetic fields

Sex differences in tobacco use, attempts to quit smoking, and cessation among dual users of cigarettes and e-cigarettes: Longitudinal findings from the US Population Assessment of Tobacco and Health Study

SignificanceA growing number of adults use more than one tobacco product, with dual use of cigarettes and e-cigarettes being the most common combination. Monitoring sex disparities in tobacco use is a public health priority. However, little is known regarding whether dual users differ by sex. MethodsData came from Waves 4–6 (12/2016–11/2021) of the Population Assessment of Tobacco and Health Study, a US nationally-representative longitudinal survey. This analysis included current adult dual users of cigarettes and e-cigarettes. We used weighted generalized estimating equations to assess the association between sex and (1) making a cigarette quit attempt (n = 1882 observations from n = 1526 individuals) and (2) smoking cessation (n = 2081 observations from n = 1688 individuals) across two wave pairs, adjusting for age, education, ethnicity, time-to-first cigarette after waking, and e-cigarette use frequency. ResultsAmong US dual users, 14.1% (95% Confidence Intervals [Cl] = 11.9–16.4) of females and 23.4% (20.0–26.9) of males were young adults (aged 18–24), 11.7% (9.2–14.2) of females and 14.4% (11.6–17.2) of males had <high school education, and 82.2% (79.4–84.5) of females and 78.7% (75.1–82.4) of males were white. Overall, 44.9% (41.6–48.1) of females compared with 37.4% (33.5–41.3) of males made an attempt to quit smoking between a baseline and follow-up wave (Adjusted Risk Ratio [ARR] = 1.23, 1.05–1.45). In contrast, there were no apparent differences between females (22.1%, 19.0–25.2) and males (24.3%, 21.5–27.1) in smoking cessation (ARR = 1.06, 0.84–1.35). ConclusionUS females who dual use e-cigarettes and cigarettes were more likely to attempt to quit smoking, but not more likely to succeed at quitting, than males.

Effect of the mixing of s-wave and chiral p-wave pairings on electrical shot noise properties of normal metal/superconductor tunnel junctions

Abstract We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet $s$-wave and chiral triplet $p$-wave pairing due to broken inversion symmetry. We investigate how the shot noise properties vary as the relative amplitude between the two parity components in the pairing potential is changed. It is demonstrated that some characteristics of the electrical shot noise properties of such tunnel junctions may depend sensitively on the relative amplitude between the two parity components in the pairing potential, and some significant changes may occur in the electrical shot noise properties when the relative amplitude between the two parity components is varied from the singlet $s$-wave pairing dominated regime to the chiral triplet $p$-wave pairing dominated regime. In the chiral triplet $p$-wave pairing dominated regime, the ratio of noise power to electric current is close to $2e$ both in the in-gap and in the out-gap region. In the singlet $s$-wave pairing dominated regime, the value of this ratio is close to $4e$ in the inner gap region but may reduce to about $2e$ in the outer gap region as the relative amplitude of the chiral triplet pairing component is increased. The variations of the differential shot noise with the bias voltage also exhibit some significantly different features in different regimes. Such different features can serve as useful diagnostic tools for the determination of the relative magnitude of the two parity components in the pairing potential.

Low-Energy Spin Excitations in Detwinned FeSe

Abstract Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high-T c superconductors. In iron-based superconductors, spin excitations at low energy range, especially the spin-resonance mode at E R ∼ 5k B T c, are important for understanding the superconductivity. Here, we use inelastic neutron scattering (INS) to investigate the symmetry and in-plane wave-vector dependence of low-energy spin excitations in uniaxial-strain detwinned FeSe. The low-energy spin excitations (E &lt; 10 meV) appear mainly at Q = (±1, 0) in the superconducting state (T ≲ 9 K) and the nematic state (T ≲ 90 K), confirming the constant C 2 rotational symmetry and ruling out the C 4 mode at E ≈ 3 meV reported in a prior INS study. Moreover, our results reveal an isotropic spin resonance in the superconducting state, which is consistent with the s ± wave pairing symmetry. At slightly higher energy, low-energy spin excitations become highly anisotropic. The full width at half maximum of spin excitations is elongated along the transverse direction. The Q-space isotropic spin resonance and highly anisotropic low-energy spin excitations could arise from dyz intra-orbital selective Fermi surface nesting between the hole pocket around Γ point and the electron pockets centered at M X point.

Structural phase transition, s±-wave pairing, and magnetic stripe order in bilayered superconductor La3Ni2O7 under pressure

Motivated by the recently discovered high-Tc superconductor La3Ni2O7, we comprehensively study this system using density functional theory and random phase approximation calculations. At low pressures, the Amam phase is stable, containing the Y2− mode distortion from the Fmmm phase, while the Fmmm phase is unstable. Because of small differences in enthalpy and a considerable Y2− mode amplitude, the two phases may coexist in the range between 10.6 and 14 GPa, beyond which the Fmmm phase dominates. In addition, the magnetic stripe-type spin order with wavevector (π, 0) was stable at the intermediate region. Pairing is induced in the s±-wave channel due to partial nesting between the M = (π, π) centered pockets and portions of the Fermi surface centered at the X = (π, 0) and Y = (0, π) points. This resembles results for iron-based superconductors but has a fundamental difference with iron pnictides and selenides. Moreover, our present efforts also suggest La3Ni2O7 is qualitatively different from infinite-layer nickelates and cuprate superconductors.

Ordered phases and superconductivity in two-dimensional electron systems subject to pair spin-orbit interaction

Pair spin-orbit interaction can emerge in strongly interacting systems characterized by a large spin-orbit coupling. Here we study the role of this interaction in stabilizing ordered and unconventional superconducting phases. We find that, if the system avoids superconductivity, the order realized is a combination of charge density and spin-vorticity waves. The latter is reminiscent of a loop-current state, albeit in the spin channel, rather than in the charge channel. If the system becomes superconducting, the order parameter assumes the form of a paired density wave, i.e., pairing occurs at finite momentum. Intriguingly, one of the possible pairings acquires a form analogous to Amperean superconductivity. However, the order parameter here is always a blend of paired density wave and Amperean pairing, rather than being purely one or the other. Published by the American Physical Society 2024

Crossover from clean to dirty superconducting limit in YBCO films with modulated disorder

Magnetotransport measurements have been carried out for pristine and irradiated Y Ba2Cu3O7−x films. The measurements reveal a crossover from the clean superconducting limit to the dirty one with an increase in the impurity scattering rate Γ produced by a certain dose of irradiation. For the clean limit, the critical temperature Tc0 decreases with Γ, while the initial slope K=|dHc2/dT|Tc0 increases. We find a nice agreement between these experimental data and a model of d-wave superconductors with anisotropic impurity scattering. Such dose-dependencies of Tc0 and K reveal the superconducting coherence length ξ0 to be quasi-invariant in the clean limit. For the dirty limit, ξ0 increases with Γ due to a decrease in both the quantities Tc0 and K. Though, this decrease appears slower than predicted by the textbook picture of d-wave superconductors. Such discrepancy can be produced by an irradiation-induced modulated disorder responsible for the formation of (d+s)-wave pairing.

Electronic correlation and s-wave pairing effects in hole-doped LiNbO2: A DFT+DMFT study

We compute the electronic many-particle properties of the normal and s-wave superconducting state of hole-doped lithium niobite (LiNbO2), taking into account local dynamical correlations by means of density functional plus dynamical mean-field theory (DFT+DMFT). Our results for the one-band Hubbard model yield a consistent picture for the electronic structure reconstruction of Li x NbO2 and point at the importance of single-band electron correlations for understanding the emergent collective superfluid spectra as well as the hidden nature of the Fermi liquid electronic state that might host a s-wave superconducting phase at low teperatures.

S^{±}-Wave Pairing and the Destructive Role of Apical-Oxygen Deficiencies in La_{3}Ni_{2}O_{7} under Pressure.

Recently, the bilayer perovskite nickelate La_{3}Ni_{2}O_{7} has been reported to show evidence of high-temperature superconductivity (SC) under a moderate pressure of about 14GPa. To investigate the superconducting mechanism, pairing symmetry, and the role of apical-oxygen deficiencies in this material, we perform a random-phase approximation based study on a bilayer model consisting of the d_{x^{2}-y^{2}} and d_{3z^{2}-r^{2}} orbitals of Ni atoms in both the pristine crystal and the crystal with apical-oxygen deficiencies. Our analysis reveals an s^{±}-wave pairing symmetry driven by spin fluctuations. The crucial role of pressure lies in that it induces the emergence of the γ pocket, which is involved in the strongest Fermi-surface nesting. We further found the emergence of local moments in the vicinity of apical-oxygen deficiencies, which significantly suppresses the T_{c}. Therefore, it is possible to significantly enhance the T_{c} by eliminating oxygen deficiencies during the synthesis of the samples.

Enhanced cuprate superconductivity from elongated to compressed coordination

In 1986 Professor Müller and Bednorz discovered the historic superconductor of LaBaCuO (La214) that opens the prelude of unprecedented era for high Tc superconductivity research worldwide. The Jahn Teller effects combining with strong interlayer Coulomb interactions lead to the elongated copper oxygen coordination in La214, giving rise to the orbital order scenario that the Cu3dx2-y2 locates near Fermi surface while the 3dz2 is far below without contributions to the conductivity, hence single band model is favorite. We recently discovered a new type of cuprate superconductor Ba2CuO4-y (Ba214) synthesized at extreme high oxygen pressure that shares a similar crystal structure to the classical La214 but with notably a very rare compressive type octahedron. The compressed octahedron coordination results from the longer in plane CuO bond length than that for apical oxygen bond. The compressed octahedron will lead to a reversed orbital order, i.e. the 3dz2 will be lifted above 3dx2-y2,which is generally considered unfavorable to superconductivity based on the current theories of high Tc cuprates. Ba214 however exhibits bulk superconducting transition with Tc above 70 K at ambient pressure, a surprisingly 80 % enhancement from that for isostructural La214. Here we briefly introduce the unique structure features as well research progress for Ba214, indicating the paradigm shifts roles of 3dz2 orbital in (I) enhancing cuprate superconductivity, (II) favoring multiband scenario; (III) enabling the s wave pairing mechanism.

Vector localized and periodic waves for the matrix Hirota equation with sign-alternating nonlinearity via the binary Darboux transformation

Dynamical properties of vector localized and periodic waves hold significant importance in the study of physical systems. In this work, we investigate the matrix Hirota equation with sign-alternating nonlinearity via the binary Darboux transformation. For the two interacting components, we construct the binary Darboux transformation formulas, vector localized, and periodic wave solutions. Via those solutions, different kinds of nonlinear waves can be achieved, including rogue waves, solitons, positons, and periodic waves. When the imaginary part of the spectral parameter is not zero, eye-shaped rogue waves appear in one component, and the twisted rogue wave pairs in the other component. As the spectral parameter is real, we derive distinct forms of vector localized and periodic waves on the non-zero background, such as the vector solitons, positons, periodic waves, breathers on the periodic wave background, and rational solitons. These results may be valuable in this investigation of nonlinear waves in physical systems.

Evolution of magnetic correlation in an inhomogeneous square lattice

We explore the magnetic properties of a two-dimensional Hubbard model on an inhomogeneous square lattice, which provides a platform for tuning the bandwidth of the flat band. In its limit, this inhomogeneous square lattice turns into a Lieb lattice, and it exhibits abundant properties due to the flat band structure at the Fermi level. By using the determinant quantum Monte Carlo simulation, we calculate the spin susceptibility, double occupancy, magnetization, spin structure factor, and effective pairing interaction of the system. It is found that the antiferromagnetic correlation is suppressed by the inhomogeneous strength and that the ferromagnetic correlation is enhanced. Both the antiferromagnetic correlation and ferromagnetic correlation are enhanced as the interaction increases. It is also found that the effective $d$-wave pairing interaction is suppressed by the increasing inhomogeneity. In addition, we also study the thermodynamic properties of the inhomogeneous square lattice, and the calculation of specific heat provides good support for our point. Our intensive numerical results provide a rich magnetic phase diagram over both the inhomogeneity and interaction.

High-temperature Majorana corner modes in a d+id′ superconductor heterostructure: Application to twisted bilayer cuprate superconductors

The realization of Majorana corner modes generally requires unconventional superconducting pairing or $s$-wave pairing. However, the bulk nodes in unconventional superconductors and the low $T_c$ of $s$-wave superconductors are not conducive to the experimental observation of Majorana corner modes. Here we show the emergence of a Majorana corner mode at each corner of a two-dimensional topological insulator in proximity to a $d+id'$ pairing superconductor, such as heavily doped graphene or especially a twisted bilayer of a cuprate superconductor, e.g., Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, which has recently been proposed as a fully gapped chiral $d_{x^2-y^2}+id_{xy}$ superconductor with $T_c$ close to its native 90 K, and an in-plane magnetic field. By numerical calculation and intuitive edge theory, we find that the interplay of the proximity-induced pairing and Zeeman field can introduce opposite Dirac masses on adjacent edges of the topological insulator, which creates one zero-energy Majorana mode at each corner. Our scheme offers a feasible route to achieve and explore Majorana corner modes in a high-temperature platform without bulk superconductor nodes.

Pair density wave in the doped three-band Hubbard model on two-leg square cylinders

A pair density wave (PDW) is a superconducting (SC) state with a spatially modulated order parameter. Although much is known about the properties of the PDW state, its realization in microscopic models with divergent susceptibility has been challenging. Here we report a density-matrix renormalization group study of a three-band Hubbard model (also known as the Emery model) for cuprates on long two-leg square cylinders. Upon light doping, we find that the ground state of the system is consistent with that of a PDW state with mutually commensurate and power-law SC, charge (CDW), and spin (SDW) density wave correlations. The SC correlations are dominant between neighboring Cu sites with $d$-wave pairing symmetry. Interestingly, we find that the near-neighbor interactions, especially the near-neighbor attractive ${V}_{pd}$ interaction between neighboring Cu and oxygen sites, can notably enhance the SC correlations while simultaneously suppressing the CDW correlations. For a modestly strong attractive ${V}_{pd}$, the SC correlations become quasi-long-ranged with a divergent PDW susceptibility.

Phase fluctuations in two-dimensional superconductors and pseudogap phenomenon

We study the phase fluctuations in the normal state of generic two-dimensional superconducting systems with $s$-wave pairing. The effect of phase fluctuations of the pairing fields can be dealt with perturbatively using disorder averaging, after we treat the local superconducting order parameter as a static disordered background. It is then confirmed that the phase fluctuations above the two-dimensional Berezinskii-Kosterlitz-Thouless transition lead to a significant broadening of the single-particle spectrum, giving birth to the pseudogap phenomenon. Quantitatively, the broadening of spectral weights near the BCS gap is characterized by the ratio of the superconducting coherence length and the spatial correlation length of the superconducting pairing order parameter. Our results are tested on the fermionic attractive-$U$ Hubbard model on the square lattice, using the unbiased determinant quantum Monte Carlo method and stochastic analytic continuation.