Magnetic fluctuations in n-type high-TcT_c superconductors reveal breakdown of fermiology

By combining experimental measurements of the quasiparticle and dynamical magnetic properties of optimally electron-doped Pr$_{0.88}$LaCe$_{0.12}$CuO$_4$ with theoretical calculations we demonstrate that the conventional fermiology approach cannot possibly account for the magnetic fluctuations in these materials. In particular, we perform tunneling experiments on the very same sample for which a dynamical magnetic resonance has been reported recently and use photoemission data by others on a similar sample to characterize the fermionic quasiparticle excitations in great detail. We subsequently use this information to calculate the magnetic response within the conventional fermiology framework as applied in a large body of work for the hole-doped superconductors to find a profound disagreement between the theoretical expectations and the measurements: this approach predicts a step-like feature rather than a sharp resonance peak, it underestimates the intensity of the resonance by an order of magnitude, it suggests an unreasonable temperature dependence of the resonance, and most severely, it predicts that most of the spectral weight resides in incommensurate wings which are a key feature of the hole-doped cuprates but have never been observed in the electron-doped counterparts. Our findings strongly suggest that the magnetic fluctuations reflect the quantum-mechanical competition between antiferromagnetic and superconducting orders.Comment: 10 pages, 9 figures, 1 tabl

Proportion of neonatal readmission attributed to length of stay for childbirth: a population-based cohort study

Objective: Most literature on length of stay (LOS) for childbirth focuses on ‘early’ discharge as opposed to ‘optimal’ time of discharge and has conflicting results due to heterogeneous definitions of ‘early’ discharge and differing eligibility criteria for these programmes. We aimed to determine the LOS associated with the lowest neonatal readmission rate following childbirth by examining the incidence pattern of neonatal readmission for different LOS using the Kitagawa decomposition. Design: Retrospective cohort study using administrative hospitalisation data. Setting: Canada (excluding Quebec) from 2003 to 2010. Patients: Term, singleton live births without congenital anomalies. Interventions: LOS for childbirth. Main outcome measure: Neonatal readmissions within 30 days of birth. Results: 1 875 322 live births were included. Neonatal LOS peaked at day 1 (47.3%) after vaginal birth and day 3 (49.3%) following caesarean section; 4.2% of infants were readmitted following vaginal birth and 2.2% after caesarean section. In 2008–2010, most readmissions occurred among infants discharged in the first 2 days (83.8%) following a vaginal birth and among infants discharged in the first 3 days (81.7%) following a caesarean birth. Readmissions increased from 4.1% in 2003–2005 to 4.6% in 2008–2010 among vaginal births and from 2.0% to 2.4% among caesarean births and occurred mostly due to changes in the day-specific readmission rates and not due to reductions in LOS. Conclusions: Patterns of readmission suggest that readmission rates are lowest following a 1–2-day stay following a vaginal birth and a 2–4-day stay following a caesarean birth given the outpatient support in the community

Magnetic form factor of SrFe2_2As2_2

Neutron diffraction measurements have been carried out to investigate the magnetic form factor of the parent SrFe2As2 system of the iron-based superconductors. The general feature is that the form factor is approximately isotropic in wave vector, indicating that multiple d-orbitals of the iron atoms are occupied as expected based on band theory. Inversion of the diffraction data suggests that there is some elongation of the spin density toward the As atoms. We have also extended the diffraction measurements to investigate a possible jump in the c-axis lattice parameter at the structural phase transition, but find no detectable change within the experimental uncertainties

Spin-Charge Coupling in lightly doped Nd2−x_{2-x}Cex_{x}CuO4_4

We use neutron scattering to study the influence of a magnetic field on spin structures of Nd$_2$CuO$_4$. On cooling from room temperature, Nd$_2$CuO$_4$ goes through a series of antiferromagnetic (AF) phase transitions with different noncollinear spin structures. While a c-axis aligned magnetic field does not alter the basic zero-field noncollinear spin structures, a field parallel to the CuO$_2$ plane can transform the noncollinear structure to a collinear one ("spin-flop" transition), induce magnetic disorder along the c-axis, and cause hysteresis in the AF phase transitions. By comparing these results directly to the magnetoresistance (MR) measurements of Nd$_{1.975}$Ce$_{0.025}$CuO$_4$, which has essentially the same AF structures as Nd$_2$CuO$_4$, we find that a magnetic-field-induced spin-flop transition, AF phase hysteresis, and spin c-axis disorder all affect the transport properties of the material. Our results thus provide direct evidence for the existence of a strong spin-charge coupling in electron-doped copper oxides.Comment: 12 pages, 12 figure

Influence of definition based versus pragmatic birth registration on international comparisons of perinatal and infant mortality: population based retrospective study

Objectives To examine variations in the registration of extremely low birthweight and early gestation births and to assess their effect on perinatal and infant mortality rankings of industrialised countries