Using self-consistent mean-field and functional renormalization-group approaches, we show that s-wave pairing symmetry is robust in the heavily electron-doped iron chalcogenides AFe 2Àx Se 2 , where A ¼ K;Cs. Recent neutron scattering experiments suggest that the effective nearest-neighbor spin exchange may be ferromagnetic in chalcogenides. This is different from the iron pnictides, where the nearest-neighbor magnetic exchange coupling is believed to be antiferromagnetic and leads to strong competition between s-wave and d-wave pairing in the electron-overdoped region. Our finding of a robust s-wave pairing in ðK;CsÞFe 2Àx Se 2 differs from the d-wave pairing result obtained by other theories where nonlocal bare interaction terms and the next-to-nearest-neighbor J 2 term are underestimated. Detecting the pairing symmetry in ðK;CsÞFe 2Àx Se 2 may hence provide important insights regarding the mechanism of superconducting pairing in iron-based superconductors.

We present the ground state pairing correlations in the S4 symmetric microscopic model for iron-based superconductors, computed with the constrained-path Monte Carlo method. For various electron fillings and interaction strengths, we find that the sxy pairing dominate over other pairing correlations and are positive when the pair separation exceeds several lattice constants, whatever for iron pnictides and iron chlcogenides. These ground state properties, especially the long range part pairing correlations re-conform the previous finite temperature results published in Phys. Rev. Lett. 110, 107002(2013). We further our study by including the nearest neighbour interaction V and it is found that the sxy pairing correlation is slightly suppressed by the increasing V .

Artificial wetlands such as coastal saltpans have replaced a number of coastal natural habitats worldwide and may have accommodated specific waterbird populations in the East Asian–Australasian Flyway (EAAF). The role of saltpans in the EAAF as foraging grounds for shorebirds is widely recognized, although their role as breeding grounds for waterbirds is very limited and contradictory. The Nanpu saltpans in northern Bohai Bay, China, are one of the largest saltpan complexes in the world. In this study, we monitored the nesting success (852 nests) of pied avocets (Recurvirostra avosetta) during three breeding seasons (2015, 2016, and 2018) in the Nanpu saltpans. The nest daily survival rate (DSR) was 0.970; hence, nest survival over the 27 exposure days was 44%. The apparent nest success was 51%. Surprisingly, 55% of nests failed during the laying period. Flooding and nest abandonment were the main causes of nest failure during both the laying and incubation periods. We found a strong positive relationship between the DSR and nest age, with nests that approached hatching having a greater probability of survival than freshly started nests. We also found a strong negative relationship between the DSR and precipitation, with the highest DSR observed for nests that experienced no precipitation. The DSR decreased over the course of the 71-days nesting season and followed a linear trend. The DSR was also density dependent and decreased slightly when nests were denser. A literature review showed that nest survival in the Nanpu saltpans was average compared with that of other studies and that nest success in artificial wetlands was significantly higher than that in natural wetlands or both habitats. Nevertheless, nest success decreased with the study date, suggesting that that breeding conditions for the pied avocet are worsening with time. The loss of saltpans could negatively affect the population of avocets and other ground-nesting waterbird species; therefore, conservation actions and research efforts should be strengthened to understand and conserve these functional wetlands for waterbirds.

No abstract

No abstract