Intricacies of the Co3+^{3+} spin state in Sr2_2Co0.5_{0.5}Ir0.5_{0.5}O4_4: an x-ray absorption and magnetic circular dichroism study

We report on a combined soft x-ray absorption and magnetic circular dichroism (XMCD) study at the Co-$L_{3,2}$ on the hybrid 3$d$/5$d$ solid state oxide Sr$_2$Co$_{0.5}$Ir$_{0.5}$O$_4$ with the K$_2$NiF$_4$ structure. Our data indicate unambiguously a pure high spin state $(S=2)$ for the Co$^{3+}$ (3$d^6$) ions with a significant unquenched orbital moment $L_z/2S_z=0.25$ despite the sizeable elongation of the CoO$_6$ octahedra. Using quantitative model calculations based on parameters consistent with our spectra, we have investigated the stability of this high spin state with respect to the competing low spin and intermediate spin states.Comment: 7 pages, 4 figure

Hour-glass magnetic excitations induced by nanoscopic phase separation in cobalt oxides La2−x_{2-x}Srx_xCoO4_4

The magnetic excitations in the cuprate superconductors might be essential for an understanding of high-temperature superconductivity. In these cuprate superconductors the magnetic excitation spectrum resembles an hour-glass and certain resonant magnetic excitations within are believed to be connected to the pairing mechanism which is corroborated by the observation of a universal linear scaling of superconducting gap and magnetic resonance energy. So far, charge stripes are widely believed to be involved in the physics of hour-glass spectra. Here we study an isostructural cobaltate that also exhibits an hour-glass magnetic spectrum. Instead of the expected charge stripe order we observe nano phase separation and unravel a microscopically split origin of hour-glass spectra on the nano scale pointing to a connection between the magnetic resonance peak and the spin gap originating in islands of the antiferromagnetic parent insulator. Our findings open new ways to theories of magnetic excitations and superconductivity in cuprate superconductors.Comment: Nature Communications 5, 5731 (2014

Electronic and magnetic nano phase separation in cobaltates La2−x_{2-x}Srx_{x}CoO4_4

The single-layer perovskite cobaltates have attracted enormous attention due to the recent observation of hour-glass shaped magnetic excitation spectra which resemble the ones of the famous high-temperature superconducting cuprates. Here, we present an overview of our most recent studies of the spin and charge correlations in floating-zone grown cobaltate single crystals. We find that frustration and a novel kind of electronic and magnetic nano phase separation are intimately connected to the appearance of the hour-glass shaped spin excitation spectra. We also point out the difference between nano phase separation and conventional phase separation.Comment: * plenary talk SUPERSTRIPES conference 201

Gain and time resolution of 45 μ\mum thin Low Gain Avalanche Detectors before and after irradiation up to a fluence of 101510^{15} neq_{eq}/cm2^2

Low Gain Avalanche Detectors (LGADs) are silicon sensors with a built-in charge multiplication layer providing a gain of typically 10 to 50. Due to the combination of high signal-to-noise ratio and short rise time, thin LGADs provide good time resolutions. LGADs with an active thickness of about 45 $\mu$m were produced at CNM Barcelona. Their gains and time resolutions were studied in beam tests for two different multiplication layer implantation doses, as well as before and after irradiation with neutrons up to $10^{15}$ n$_{eq}$/cm$^2$. The gain showed the expected decrease at a fixed voltage for a lower initial implantation dose, as well as for a higher fluence due to effective acceptor removal in the multiplication layer. Time resolutions below 30 ps were obtained at the highest applied voltages for both implantation doses before irradiation. Also after an intermediate fluence of $3\times10^{14}$ n$_{eq}$/cm$^2$, similar values were measured since a higher applicable reverse bias voltage could recover most of the pre-irradiation gain. At $10^{15}$ n$_{eq}$/cm$^2$, the time resolution at the maximum applicable voltage of 620 V during the beam test was measured to be 57 ps since the voltage stability was not good enough to compensate for the gain layer loss. The time resolutions were found to follow approximately a universal function of gain for all implantation doses and fluences.Comment: 17 page

Household livelihood diversification in rural Africa

Open Access Article; Published online: 06 Jan 2022Diversification is a common livelihood strategy for rural households in developing countries, with diversification being either a choice or necessity depending on individual household contexts. Using two waves of data (from 2009 and 2011) for 1773 households from eight countries in sub-Saharan Africa, we examined livelihood diversification and its drivers. We examined livelihood diversification by considering household involvement in three livelihood activities: crop, livestock, and non-farm. Results indicated that 40% of households conducted all three livelihood activities, but there was heterogeneity in diversity levels. We used a correlated random effects model to identify the factors that pushed or pulled households to diversify their activities. Access to non-agricultural credit was positively associated with livelihood diversity as it can catalyze involvement in non-farm activities. Drought had a negative effect on livelihood diversity. Area of crop land had a positive effect on the number of livelihood activities conducted. We found that 53% of households added or removed at least one livelihood activity between 2009 and 2011, and the addition of non-farm activities was the most common change. Our results demonstrated the dynamic nature of livelihoods and importance of shocks (such as drought) and resource endowments (land) in understanding household livelihood diversification