9 research outputs found

    Out-of-equilibrium charge redistribution in a copper-oxide based superconductor by time-resolved X-ray photoelectron spectroscopy

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    Charge-transfer excitations are of paramount importance for understanding the electronic structure of copper-oxide based high-temperature superconductors. In this study, we investigate the response of a Bi2_2Sr2_2CaCu2_2O8+δ_{\mathrm{8}+ \delta} crystal to the charge redistribution induced by an infrared ultrashort pulse. Element-selective time-resolved core-level photoelectron spectroscopy with a high energy resolution allows disentangling the dynamics of oxygen ions with different coordination and bonds thanks to their different chemical shifts. Our experiment shows that the O\,1s1s component arising from the Cu-O planes is significantly perturbed by the infrared light pulse. Conversely, the apical oxygen, also coordinated with Sr ions in the Sr-O planes, remains unaffected. This result highlights the peculiar behavior of the electronic structure of the Cu-O planes. It also unlocks the way to study the out-of-equilibrium electronic structure of copper-oxide-based high-temperature superconductors by identifying the O\,1s1s core-level emission originating from the oxygen ions in the Cu-O planes. This ability could be critical to gain information about the strongly-correlated electron ultrafast dynamical mechanisms in the Cu-O plane in the normal and superconducting phases

    Suppression of the vacuum space-charge effect in fs-photoemission by a retarding electrostatic front lens

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    The performance of time-resolved photoemission experiments at fs-pulsed photon sources is ultimately limited by the e–e Coulomb interaction, downgrading energy and momentum resolution. Here, we present an approach to effectively suppress space-charge artifacts in momentum microscopes and photoemission microscopes. A retarding electrostatic field generated by a special objective lens repels slow electrons, retaining the k-image of the fast photoelectrons. The suppression of space-charge effects scales with the ratio of the photoelectron velocities of fast and slow electrons. Fields in the range from −20 to −1100 V/mm for Ekin_{kin} = 100 eV to 4 keV direct secondaries and pump-induced slow electrons back to the sample surface. Ray tracing simulations reveal that this happens within the first 40 to 3 μm above the sample surface for Ekin_{kin} = 100 eV to 4 keV. An optimized front-lens design allows switching between the conventional accelerating and the new retarding mode. Time-resolved experiments at Ekin_{kin} = 107 eV using fs extreme ultraviolet probe pulses from the free-electron laser FLASH reveal that the width of the Fermi edge increases by just 30 meV at an incident pump fluence of 22 mJ/cm2^2 (retarding field −21 V/mm). For an accelerating field of +2 kV/mm and a pump fluence of only 5 mJ/cm2^2, it increases by 0.5 eV (pump wavelength 1030 nm). At the given conditions, the suppression mode permits increasing the slow-electron yield by three to four orders of magnitude. The feasibility of the method at high energies is demonstrated without a pump beam at Ekin_{kin} = 3830 eV using hard x rays from the storage ring PETRA III. The approach opens up a previously inaccessible regime of pump fluences for photoemission experiments

    Variation in the risk of colorectal cancer in families with Lynch syndrome: a retrospective cohort study

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    Background: Existing clinical practice guidelines for carriers of pathogenic variants of DNA mismatch repair genes (Lynch syndrome) are based on the mean age-specific cumulative risk (penetrance) of colorectal cancer for all carriers of pathogenic variants in the same gene. We aimed to estimate the variation in the penetrance of colorectal cancer between carriers of pathogenic variants in the same gene by sex and continent of residence. Methods: In this retrospective cohort study, we sourced data from the International Mismatch Repair Consortium, which comprises 273 members from 122 research centres or clinics in 32 countries from six continents who are involved in Lynch syndrome research. Families with at least three members and at least one confirmed carrier of a pathogenic or likely pathogenic variant in a DNA mismatch repair gene (MLH1, MSH2, MSH6, or PMS2) were included. The families of probands with known de-novo pathogenic variants were excluded. Data were collected on the method of ascertainment of the family, sex, carrier status, cancer diagnoses, and ages at the time of pedigree collection and at last contact or death. We used a segregation analysis conditioned on ascertainment to estimate the mean penetrance of colorectal cancer and modelled unmeasured polygenic factors to estimate the variation in penetrance. The existence of unknown familial risk factors modifying colorectal cancer risk for Lynch syndrome carriers was tested by use of a Wald p value for the null hypothesis that the polygenic SD is zero. Findings: 5585 families with Lynch syndrome from 22 countries were eligible for the analysis. Of these, there were insufficient numbers to estimate penetrance for Asia and South America, and for those with EPCAM variants. Therefore, we used data (collected between July 11, 2014, and Dec 31, 2018) from 5255 families (1829 MLH1, 2179 MSH2, 798 MSH6, and 449 PMS2), comprising 79 809 relatives, recruited in 15 countries in North America, Europe, and Australasia. There was strong evidence of the existence of unknown familial risk factors modifying colorectal cancer risk for Lynch syndrome carriers (pT variant. The variation was especially prominent for MLH1 and MSH2 variant carriers, depending on gene, sex and continent, with 7–56% of carriers having a colorectal cancer penetrance of less than 20%, 9–44% having a penetrance of more than 80%, and only 10–19% having a penetrance of 40–60%. Interpretation: Our study findings highlight the important role of risk modifiers, which could lead to personalised risk assessments for precision prevention and early detection of colorectal cancer for people with Lynch syndrome. Funding: National Health and Medical Research Council, Australia
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