S-wave Component Research Articles

Analysis of the semileptonic decay [formula omitted

Using data collected by the fixed target Fermilab experiment FOCUS, we present several first measurements for the semileptonic decay D0→K¯0π−μ+ν. Using a model that includes a K¯0π−s-wave component, we measure the form factor ratios to be rv=1.71±0.68±0.34 and r2=0.91±0.37±0.10 and the s-wave amplitude to be A=0.35±0.22±0.05 GeV−1. Finally, we measure the vector semileptonic branching ratio Γ(D0→K*(892)−μ+ν)Γ(D0→K¯0π−π+)=0.337±0.034±0.013.

The component masses of the cataclysmic variable V347 Puppis

We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of KR= 198 ± 5 km s−1. The rotational velocity of the secondary star in V347 Pup is found to be v sin i= 131 ± 5 km s−1 and the system inclination is i= 840 ± 23. From these parameters we obtain masses of M1= 0.63 ± 0.04 M⊙ for the white dwarf primary and M2= 0.52 ± 0.06 M⊙ for the M0.5V secondary star, giving a mass ratio of q= 0.83 ± 0.05. On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc.

Threshold production of the [formula omitted] in a polarized proton reaction

We compute the cross sections of the Θ+ production near threshold for a polarized proton reaction, p→p→→Σ+Θ+ which was recently proposed to determine unambiguously the parity of Θ+. Within theoretical uncertainties the cross sections for the allowed spin configuration are estimated; it is of order of one microbarn for the positive parity Θ+ and about 1/10 microbarn for the negative parity Θ+ in the threshold energy region, where the s-wave component dominates.

The masses of the cataclysmic variables AC Cancri and V363 Aurigae

We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variables AC Cnc and V363 Aur (= Lanning 10). There is evidence of irradiation on the inner hemisphere of the secondary star in both systems, which we correct for using a model that reproduces the observations remarkably well. We find the radial velocity of the secondary star in AC Cnc to be KR= 176 ± 3 km s−1 and its rotational velocity to be v sin i= 135 ± 3 km s−1. From these parameters we obtain masses of M1= 0.76 ± 0.03 M⊙ for the white-dwarf primary and M2= 0.77 ± 0.05 M⊙ for the K2 ± 1V secondary star, giving a mass ratio of q= 1.02 ± 0.04. We measure the radial and rotational velocities of the G7 ± 2V secondary star in V363 Aur to be KR= 168 ± 5 km s−1 and v sin i= 143 ± 5 km s−1, respectively. The component masses of V363 Aur are M1= 0.90 ± 0.06 M⊙ and M2= 1.06 ± 0.11 M⊙, giving a mass ratio of q= 1.17 ± 0.07. The mass ratios for AC Cnc and V363 Aur fall within the theoretical limits for dynamically and thermally stable mass transfer. Both systems are similar to the SW Sex stars, exhibiting single-peaked emission lines with transient absorption features, high-velocity S-wave components and phase-offsets in their radial-velocity curves. The Balmer lines in V363 Aur show a rapid increase in flux around phase 0 followed by a rapid decrease, which we attribute to the eclipse of an optically thick region at the centre of the disc. This model could also account for the behaviour of other SW Sex stars where the Balmer lines show only a shallow eclipse compared to the continuum.

One-neutron halo structure inC15

The one- or two-neutron removal reactions as well as reaction cross sections for C-14,C-15 on carbon target have been studied by using 110A MeV Ne-22 primary beam on Riken Projectile Fragment Separator in RIKEN. The longitudinal momentum distributions of C-13,C-14 fragments from C-15 and C-13 fragments from C-14 breakup have been measured at 83A MeV by means of direct time-of-flight method. Full width at half maximum (FWHM) of the distributions have been determined to be 71+/-9 MeV/c and 223+/-28 MeV/c for C-14 and C-13 from C-15, and 195+/-21 MeV/c for C-13 from C-14. The FWHM for C-13 fragments from C-15 and C-14 breakup are consistent with the Goldhaber model's prediction. While the FWHM of C-14 fragments from C-15 is much smaller, which confirms the experimental results from MSU and GANIL, an anomalous enhancement from its neighbors has been observed in the measured reaction cross section of C-15. The experimental data are discussed in the framework of the Glauber model. The analysis of both the fragment momentum distributions and reaction cross sections indicates a dominant s-wave component in the ground state of C-15.

DW Cancri: a magnetic VY Scl star with an orbital period of 86 min

We present the first time-resolved spectroscopic study of the cataclysmic variable DW Cancri. We have determined an orbital period of 86.10 +- 0.05 min, which places the system very close to the observed minimum period of hydrogen-rich cataclysmic variables. This invalidates previous speculations of DW Cnc being either a permanent superhumper below the period minimum or a nova-like variable with an orbital period longer than 3 hours showing quasi-periodic oscillations. The Balmer and HeI lines have double-peaked profiles and exhibit an intense S-wave component moving with the orbital period. Remarkably, the Balmer and HeI radial velocity curves are modulated at two periods: 86.10 +- 0.05 min (orbital) and 38.58 +- 0.02 min. The same short period is found in the equivalent width variations of the single-peaked HeII 4686 line. We also present time-resolved photometry of the system which shows a highly-coherent variation at 38.51 min, consistent with the short spectroscopic period. The large number of similarities with the short-period intermediate polar V1025 Cen lead us to suggest that DW Cnc is another intermediate polar below the period gap, and we tentatively identify the photometric and spectroscopic 38-min signals with the white dwarf spin period. DW Cnc has never been observed to undergo an outburst, but it occasionally exhibits low states \~2 mag fainter than its typical brightness level of V~14.5, resembling the behaviour of the high mass-transfer VY Scl stars.

Proximity effect in gold-coated YBa(2)Cu(3)O(7-delta) films studied by scanning tunneling spectroscopy.

Scanning tunneling spectroscopy on gold layers overcoating c-axis YBa(2)Cu(3)O(7-delta) (YBCO) films reveals proximity-induced gap structures. The gap size reduces exponentially with the distance from a-axis facets, indicating that the proximity effect is primarily due to the (100) YBCO facets. The penetration depth of superconductivity into the gold is approximately 30 nm, in good agreement with estimations for the dirty limit. The extrapolated gap at the interface is approximately 15 meV, similar to the value of an s-wave component of the order parameter measured at the YBCO surface in recent point-contact experiments.

Simulations of experimental conductance spectra ofYBa2Cu3Oyjunctions: Role of a longd-wave decay length and a smalliscomponent in the pair potential near the interface

Extended BTK-type theoretical methods were used for the calculation of conductance spectra of NS and NIS junctions, where S is either a d-wave or a d+is-wave superconductor, and N is a normal metal. We found that the length scale over which the bulk d-wave order parameter varies spatially near the interface (the "decay length") has a significant effect on the main features of the conductance spectra. A relatively large decay length of the order of 10-20$\xi_{0}$ together with a small $is$-wave component, can explain many peculiarities observed in the experimental conductance spectra of various junctions. We attribute the long decay length to either a reversed proximity effect in the high transparency junctions, or to the presence of a low $T_c\leq 10$K s-wave component with a much longer $\xi_{0s}\approx 10\xi_{0d}$ near the interface.

Order parameter and current-phase relation in Josephson junctions composed ofg+s-wave superconductors

Based on the analyses of bulk sensitive experimental data on penetration depths, Raman spectra, electron photoemission spectra, etc., G. M. Zhao concluded in a recent paper [Phys. Rev. B 64, 024503 (2001)] that the symmetry of high-T c superconductors belongs to the g+s-wave type. To explore the common and uncommon features of the g+s-wave pairing state with respect to the d-wave pairing state, both superconductor-insulator-superconductor junction and superconductor-normal metal-superconductor junction have been studied self-consistently in this paper using the quasiclassical theory. The current phase relation for g+s-wave superconductors Δ(s,θ)=Δ 0 (s+cos4θ) is investigated systematically as functions of s-wave component, crystal orientation angle β, as well as roughness p of the interface layer. Our results show that there exists a critical β C for a given s and p so that the current phase relation approaches asymptotically to I(φ)=I C sin(2φ) from I(φ)=I C sin(φ) as β→β C . The order parameter and β C -s relation are calculated self-consistently as interface roughness varies. Our results are compared with their counterparts in Josephson junctions with the d-wave pairing state obtained using a similar method.

Sivers function in the MIT bag model

The Sivers function, an asymmetric transverse-momentum distribution of the quarks in a transversely polarized nucleon, is calculated in the MIT bag model. The bag quark wave functions contain both S-wave and P-wave components, and their interference leads to nonvanishing Sivers function in the presence of the final state interactions. We approximate these interactions through one-gluon exchange. An estimate of another transverse momentum dependent distribution h1⊥ is also performed in the same model.

Raman study of carrier-overdoping effects on the gap in high-Tcsuperconducting cuprates

Raman scattering in the heavily overdoped (Y,Ca)Ba_2Cu_3O_{7-d} (T_c = 65 K) and Bi_2Sr_2CaCu_2O_{8+d} (T_c = 55 K) crystals has been investigated. For the both crystals, the electronic pair-breaking peaks in the A_{1g} and B_{1g} polarizations were largely shifted to the low energies close to a half of 2Delta_0, Delta_0 being the maximum gap. It strongly suggests s-wave mixing into the d-wave superconducting order parameter and the consequent manifestation of the Coulomb screening effect in the B_{1g}-channel. Gradual mixing of s-wave component with overdoping is not due to the change of crystal structure symmetry but a generic feature in all high-T_c superconducting cuprates.

Time-resolved spectroscopy of the M15 X-ray binary AC211/X2127+119

We present time-resolved spectroscopy acquired during two epochs (spaced apart by ~15 days) of the eclipsing Low Mass X-ray Binary AC211/X2127+119 in the globular cluster M15. The spectra show variations in the HeII 4686 emission line not only modulated on the orbital period, but also on time-scales of a few days. During the first epoch of observation, the emission line shows a strong S-wave superimposed on the average double-peaked profile. The line exhibits no evidence of rotational disturbance at the orbital phases when the eclipse is observed in the optical continuum. During the second epoch, no double-peak or S-wave component is present. The HeI absorption lines detected by other authors are not present in our spectra. A Doppler image of the HeII 4686 for the first epoch supports the presence of the accretion disc. No hotspot is detected, although enhanced emission at V_X=30km/s, V_Y=160 km/s is observed. We discuss the implications of this emission in the context of an X-ray heated donor star, in which case a high mass ratio and neutron star primary are implied. Finally, we speculate on the possibility of a misaligned secondary star in AC211.

Multiple components of the order parameter induced around the dx2−y2-wave vortex core

On the basis of the Bogoliubov–de Gennes theory for the two-dimensional extended Hubbard model, the vortex structure of dx2−y2-wave superconductors is analyzed. Multiple components of the order parameter are induced around the dx2−y2-wave vortex core. We study the spatial structure of the induced px±ipy and extended s-wave components. We also study the case when the antiferromagnetism (checkerboard or stripe) is induced at the vortex core. There, spin-triplet dx2−y2-wave component is also induced.

Van Hove scenario for a high Tc superconductor having a (s+d)-wave symmetry order parameter

The effects of having a van Hove singularity in the density of states on a high temperature superconductors having an (s+d)-wave symmetry order parameter (OP) are studied. It is assumed that superconductivity is due to the exchange of spin fluctuations. It is found that the two (s-wave and d-wave) components of the OP are determined by a set of coupled equations. Close to T c′ these equations are linear in Δ s and Δ d while at T=0 K, they form a set of non-linear equations in the two components of the OP. The equations for T close to T c are solved analytically to yield an expression for the transition temperature T c. The equations for T=0 K are solved numerically for different values of ω b (the cutoff frequency of the magnetic excitation responsible for superconductivity in the system). The dependence of the ratio 2 Δ(0)/ k B T c (with Δ(0)=Δ s (0) (1+ R 2) and R being the ratio of the two components of the OP at T=0 K) on ω b is shown.

Transport properties of bicrystal YBa 2Cu 3O 7− δ Josephson junctions

Transport properties, especially modulation patterns of critical current, of bicrystal YBa 2Cu 3O 7− δ Josephson junctions have been investigated. The modulation patterns of critical current at low magnetic fields indicate that the d-wave component is dominant in the CuO 2 plane of this high- T C cuprate. In 45° junctions, the minimum at zero field implies a small asymmetry in the d-wave junctions which should be seen as an evidence of the existence of s-wave component. In 24° junctions, we can also explain the patterns by an asymmetrical d-wave junction with dominant d–s Josephson coupling. Therefore, our results prefer to a mixed d- and s-wave order parameter for YBa 2Cu 3O 7− δ .

Interface roughness and proximity effect on ac-axis Josephson junction betweens-wave andd-wave superconductors

The scanning superconducting quantum interference device microscope on tri-crystal high-temperature superconductor (HTSC) samples unambiguously identifies the d-wave pairing symmetry as a predominant component. This fact was also seen clearly from the current phase relation (CPR) for an in-plane junction between HTSC's, where both $\ensuremath{\pi}$ periodicity and $2\ensuremath{\pi}$ periodicity are observed, depending on the relative crystal orientation. However, for c-axis junctions between HTSC's and conventional superconductor, ac Josephson effect shows that the main Shapino steps occur at $V=nhf/2e$ $(n$ is integer) and thus a significant s-wave component is indicated. To understand the experimental measurements, we have studied interface roughness and proximity effect on CPR of such junctions. The order parameter profiles and current phase relation are computed self-consistently using the quasiclassical theory and rough interface model. Our results suggest that the existence of a minor surface s-wave component stemming from a repulsive s-channel pairing potential in the d-wave superconductor is able to give a coherent picture.

Strong resonances in elastic scattering of radioactive21Naon protons

In a first experiment with accelerated beams at TRIUMF-ISAC, the scattering of radioactive ${}^{21}\mathrm{Na}$ ${(T}_{1/2}=22.49 \mathrm{s})$ on protons has been investigated. ${}^{21}\mathrm{Na}$ beams of typically $5\ifmmode\times\else\texttimes\fi{}{10}^{7}$ particles/s were employed while center-of-mass energies from 0.45 to 1.4 MeV were scanned and spectra with high statistics were collected. The experiment was carried out using large area silicon detectors at the TUDA facility. Three strong resonances corresponding to states in ${}^{22}\mathrm{Mg}$ have been identified at energies of 830 keV, 1115 keV, and 1311 keV, respectively. Using these data, aspects of the $T=1,$ $A=22$ mirror system and the s-wave component of the astrophysically important ${}^{21}\mathrm{Na}(p,\ensuremath{\gamma}{)}^{22}\mathrm{Mg}$ reaction are discussed.

On the Possibility of s+d Wave Superconductivity Within a Two-Band Scenario for High Tc Cuprates

A variety of different experimental results show substantial evidence that the order parameter in high-temperature superconducting copper oxides is not of pure d-wave symmetry, but that an s-wave component exists, which especially shows up in experiments that test the c-axis properties. These findings are modeled theoretically within a two-band model with interband interactions, where the superconducting order parameters in the two bands are allowed to differ in symmetry. It is found that the coupling of order parameters with different symmetries (s+d) leads to substantial enhancements of the superconducting transition temperature Tc as compared to order parameters with only s-wave symmetry. An additional enhancement factor of Tc is obtained from the coupling of the bands to the lattice where moderate couplings favor superconductivity while too strong couplings lead to electron (hole) localization and consequently suppress superconductivity.

Coupling to breakup channels using a transformed harmonic oscillator basis

The application of a recently proposed procedure for discretizing the continuum to collision processes involving weakly bound nuclei is studied. In particular, the coupling to breakup states in the collision of ${d+}^{208}\mathrm{Pb}$ at 50 MeV is discussed. For illustrative purposes, only the s-wave component of the bound state of the deuteron is considered, and the study is restricted to the case of nuclear s-wave breakup. The continuum discretization procedure provides a basis of transformed harmonic oscillator wave functions to accomplish the necessary calculations. Appropriate convergence of the elastic and breakup cross sections with increasing dimension of the basis is reported. In addition, it is shown that the results obtained converge to those of a standard continuum discretized coupled channels calculation, with the advantage that the convergence of the method is determined by only one parameter, namely the dimension of the basis.

Charge current in a ferromagnet-superconductor junction with the pairing state of broken time-reversal symmetry

We calculate the tunneling conductance spectra of a ferromagnetic metal/insulator/superconductor using the Blonder-Tinkham-Klapwijk (BTK) formulation. Two possible states for the superconductor are considered with the time reversal symmetry ($\cal{T}$) broken, i.e., $d_{x^2-y^2}+is$, or $d_{x^2-y^2}+id_{xy}$. In both cases the tunneling conductance within the gap is suppressed with the increase of the exchange interaction due to the suppression of the Andreev reflection. In the $(d_{x^2-y^2}+is)$-wave case the peaks that exist when the ferromagnet is a normal metal in the amplitude of the s-wave component due to the bound state formation are reduced symmetrically, with the increase of the exchange field, while in the $(d_{x^2-y^2}+id_{xy})$-wave case the residual density of states within the gap develops a dip around E=0 with the increase of the exchange field. These results would be useful to discriminate between $\cal{T}$-broken pairing states near the surface in high-$T_c$ superconductors