Novel multiple-band superconductor SrPt2As2

We present LDA calculated electronic structure of recently discovered superconductor SrPt2As2 with Tc=5.2K. Despite its chemical composition and crystal structure are somehow similar to FeAs-based high-temperature superconductors, the electronic structure of SrPt2As2 is very much different. Crystal structure is orthorhombic (or tetragonal if idealized) and has layered nature with alternating PtAs4 and AsPt4 tetrahedra slabs sandwiched with Sr ions. The Fermi level is crossed by Pt-5d states with rather strong admixture of As-4p states. Fermi surface of SrPt2As2 is essentially three dimensional, with complicated sheets corresponding to multiple bands. We compare SrPt2As2 with 1111 and 122 representatives of FeAs-class of superconductors, as well as with isovalent (Ba,Sr)Ni2As2 superconductors. Brief discussion of superconductivity in SrPt2As2 is also presented.Comment: 5 pages, 4 figure

Temperature and pressure evolution of the crystal structure of Ax(Fe1-ySe)2 (A = Cs, Rb, K) studied by synchrotron powder diffraction

Temperature-dependent synchrotron powder diffraction on Cs0.83(Fe0.86Se)2 revealed first order I4/m to I4/mmm structural transformation around 216{\deg}C associated with the disorder of the Fe vacancies. Irreversibility observed during the transition is likely associated with a mobility of intercalated Alkali atoms. Pressure-dependent synchrotron powder diffraction on Cs0.83(Fe1-ySe)2, Rb0.85(Fe1-ySe)2 and K0.8(Fe1-ySe)2 (y ~ 0.14) indicated that the I4/m superstructure reflections are present up to pressures of 120 kbar. This may indicate that the ordering of the Fe vacancies is present in both superconducting and non-superconductive states.Comment: 11 pages, 5 figures, 1 tabl

Electronic structure and possible pseudogap behavior in iron based superconductors

Starting from the simplified analytic model of electronic spectrum of iron - pnictogen (chalcogen) high - temperature superconductors close to the Fermi level, we discuss the influence of antiferromagneting (AFM)scattering both for stoichiometric case and the region of possible short - range order AFM fluctuations in doped compounds. Qualitative picture of the evolution of electronic spectrum and Fermi surfaces (FS) for different dopings is presented, with the aim of comparison with existing and future ARPES experiments. Both electron and hole dopings are considered and possible pseudogap behavior connected with partial FS "destruction" is demonstrated, explaining some recent experiments.Comment: 5 pages, 4 figures, published versio

Fermi surface in BaNi2_2P2_2

We report measurements of the de Haas-van Alphen (dHvA) oscillation and a band structure calculation for the pnictide superconductor BaNi$_2$P$_2$, which is isostructural to BaFe$_2$As$_2$, the mother compound of the iron-pnictide high-$T_c$ superconductor (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$. Six dHvA-frequency branches with frequencies up to $\sim$8 kT were observed, and they are in excellent agreement with results of the band-structure calculation. The determined Fermi surface is large, enclosing about one electron and hole per formula unit, and three-dimensional. This is in contrast to the small two-dimensional Fermi surface expected for the iron-pnictide high-$T_c$ superconductors. The mass enhancement is about two.Comment: To appear in J. Phys. Soc. Jpn., Vol. 78, No.

Installation, commissioning, and testing of the HB650 CM at PIP2IT

The Proton Improvement Plan-II (PIP-II) is a major upgrade to the Fermilab accelerator complex, featuring a new 800-MeV Superconducting Radio-Frequency (SRF) linear accelerator (LINAC) powering the accelerator complex to provide the world's most intense high-energy neutrino beam. This paper describes the conversion of the PIP-II Injector Test Facility (PIP2IT) cryogenic system into a test stand for PIP-II High-Beta 650 MHz (HB650) cryomodules at Fermilab's Cryomodule Test Facility (CMTF). A description of the associated mechanical, electrical, and controls modifications necessary for testing HB650 cryomodules are provided. The cooldown and warmup requirements, procedures and associated controls logic is described.Comment: 2023 Cryogenic Engineering Conference and International Cryogenic Materials Conference (CEC/ICMC

Effect of the COVID-19 pandemic response on intrapartum care, stillbirth, and neonatal mortality outcomes in Nepal: a prospective observational study

BACKGROUND: The COVID-19 pandemic response is affecting maternal and neonatal health services all over the world. We aimed to assess the number of institutional births, their outcomes (institutional stillbirth and neonatal mortality rate), and quality of intrapartum care before and during the national COVID-19 lockdown in Nepal. METHODS: In this prospective observational study, we collected participant-level data for pregnant women enrolled in the SUSTAIN and REFINE studies between Jan 1 and May 30, 2020, from nine hospitals in Nepal. This period included 12·5 weeks before the national lockdown and 9·5 weeks during the lockdown. Women were eligible for inclusion if they had a gestational age of 22 weeks or more, a fetal heart sound at time of admission, and consented to inclusion. Women who had multiple births and their babies were excluded. We collected information on demographic and obstetric characteristics via extraction from case notes and health worker performance via direct observation by independent clinical researchers. We used regression analyses to assess changes in the number of institutional births, quality of care, and mortality before lockdown versus during lockdown. FINDINGS: Of 22 907 eligible women, 21 763 women were enrolled and 20 354 gave birth, and health worker performance was recorded for 10 543 births. From the beginning to the end of the study period, the mean weekly number of births decreased from 1261·1 births (SE 66·1) before lockdown to 651·4 births (49·9) during lockdown-a reduction of 52·4%. The institutional stillbirth rate increased from 14 per 1000 total births before lockdown to 21 per 1000 total births during lockdown (p=0·0002), and institutional neonatal mortality increased from 13 per 1000 livebirths to 40 per 1000 livebirths (p=0·0022). In terms of quality of care, intrapartum fetal heart rate monitoring decreased by 13·4% (-15·4 to -11·3; p&lt;0·0001), and breastfeeding within 1 h of birth decreased by 3·5% (-4·6 to -2·6; p=0·0032). The immediate newborn care practice of placing the baby skin-to-skin with their mother increased by 13·2% (12·1 to 14·5; p&lt;0·0001), and health workers' hand hygiene practices during childbirth increased by 12·9% (11·8 to 13·9) during lockdown (p&lt;0·0001). INTERPRETATION: Institutional childbirth reduced by more than half during lockdown, with increases in institutional stillbirth rate and neonatal mortality, and decreases in quality of care. Some behaviours improved, notably hand hygiene and keeping the baby skin-to-skin with their mother. An urgent need exists to protect access to high quality intrapartum care and prevent excess deaths for the most vulnerable health system users during this pandemic period.De två sista författarna delar sistaförfattarskapet</p