Quasiparticle energy spectrum in ferromagnetic Josephson weak links

The quasiparticles energy spectrum in clean ferromagnetic weak links between conventional superconductors is calculated. Large peaks in DOS, due to a special case of Andreev reflection at the ferromagnetic barrier, correspond to spin-splitt bound states. Their energies are obtained as a function of the barrier thickness, exchange field strength, and of the macroscopic phase difference $\phi$ at the link, related to the Josephson current. In the ground state, $\phi$ can be 0 or $\pi$, depending on the ferromagnetic barrier influence. Conditions for the appearence of the zero-energy bound states (ZES) and for the spin polarized ground state (SPGS) are obtained analytically. It is shown that ZES appear only outside the weak link ground state.Comment: 11 pages, 6 figure

Josephson currents through spin-active interfaces

The Josephson coupling of two isotropic s-wave superconductors through a small, magnetically active junction is studied. This is done as a function of junction transparency and of the degree of spin-mixing occurring in the barrier. In the tunneling limit, the critical current shows an anomalous 1/T temperature dependence at low temperatures and for certain magnetic realizations of the junction. The behavior of the Josephson current is governed by Andreev bound states appearing within the superconducting gap and the position of these states in energy is tunable with the magnetic properties of the barrier. This study is done using the equilibrium part of the quasiclassical Zaitsev-Millis-Rainer-Sauls boundary condition for spin-active interfaces and a general solution of the boundary condition is found. This solution is a generalization of the one recently presented by Eschrig [M. Eschrig, Phys. Rev B 61, 9061 (2000)] for spin-conserving interfaces and allows an effective treatment of the problem of a superconductor in proximity to a magnetically active material.Comment: 8 pages + 3 eps figure

Outcomes of Early Correction of Congenital Myogenic Ptosis Using Transconjunctival Levator Plication

Introduction: Early correction of congenital ptosis may be indicated due to a risk of amblyopia or because of an abnormal head tilt. One of the main problems, of planning ptosis surgery in very young children, is the inability to measure the levator function. Aim: The aim of the article was to analyze the early correction of congenital myogenic ptosis. Methods: This was a retrospective, interventional, case series study, conducted on 12 eyes of 12 patients with unilateral, mild to moderate, congenital myogenic ptosis. Surgical correction of ptosis was performed by transconjunctival levator muscle plication. Pre- and postoperative measurements of the upper lid margin to central corneal reflex (MRD1) and upper lid skin crease height (UEC) were obtained, as well as the presence or absence of a reaction to topically applied phenylephrine 2.5% solution. Results: The mean age of the patients was 29.83 months (range 14-45 months). A negative phenylephrine test was noted in only 3 (25%) of cases. Equalization of upper lid height was achieved in 6 (50%), and a hypocorrection of up to 1 mm was noted in 4 (33%) of patients. There was only 1 hypercorrection of 1 mm, noted in the first postoperative month. In one case of hypocorrection of 2 mm, the height of the lid dropped between the 1 and 3 months follow up. Subsequent revision surgery was performed, with a good outcome. With regard to the upper lid skin crease height (UEC), the mean preoperative difference in relation to the contralateral (non-operated) lid, was 2.16 mm, whereas the average postoperative or final difference was 0.41 mm. Conclusion: Correction of myogenic ptosis in small children, using transconjunctival levator plication, in whom levator function cannot be measured, may have a satisfactory postoperative outcome

Fast photoluminescence quenching in thin films of 4,4 '-bis(2,2-diphenylvinyl)-1,1 '-biphenyl exposed to air

The photoluminescence (PL) quenching mechanism of UV light and air-exposed amorphous thin films of 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl (DPVBi), a well-known hole-transport material used in organic light-emitting diodes, is studied. Thin films of DPVBi are stable when exposed to UV light in vacuum but tend to degrade if oxygen is present simultaneously. This is evident from the changes in UV-vis absorption spectra of the latter, showing that degradation rate of DPVBi films is linearly proportional to both oxygen concentration and UV light intensity. Mass spectrometry study of such films revealed a number of different oxygen-containing molecules and fragments of DPVBi thus confirming apparent photo-oxidation process. Also, DFT study of molecular DPVBi with and without oxygen was carried out, the IR spectra calculated for the lowest energy molecules found and the results are compared with the experiment. The most sensitive to photo-oxidation is DPVBi photoluminescence, which decays exponentially with respect to the concentration of photo-oxidized DPVBi molecules (impurities). The PL quantum yield of DPVBi thin film drops to a half of its original value for 0.2% of the impurities present, at which point an average distance between DPVBi molecules (the donors) and photo-oxidized DPVBi species (acceptors) is an order of magnitude larger than the separation between two adjacent molecules. This implies a need for a long-range Forster energy transfer, which we rule out based on the lack of a donor-acceptor spectral overlap. The apparent discrepancy can be removed by postulating exciton self-diffusion in DPVBi thin films, for which there is supporting evidence in existing literature