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Excitons are realizations of a correlated many-particle wave function, specifically consisting of electrons and holes in an entangled state. Excitons occur widely in semiconductors and are dominant excitations in semiconducting organic and low-dimensional quantum materials. To efficiently harness the strong optical response and high tuneability of excitons in optoelectronics and in energy-transformation processes, access to the full wavefunction of the entangled state is critical, but has so far not been feasible. Here, we show how time-resolved photoemission momentum microscopy can be used to gain access to the entangled wavefunction and to unravel the exciton's multiorbital electron and hole contributions. For the prototypical organic semiconductor buckminsterfullerene (C 60 ), we exemplify the capabilities of exciton tomography and achieve unprecedented access to key properties of the entangled exciton state including localization, charge-transfer character, and ultrafast exciton formation and relaxation dynamics., (© 2024. The Author(s).)

In two-dimensional semiconductors, cooperative and correlated interactions determine the material's excitonic properties and can even lead to the creation of correlated states of matter. Here, we study the fundamental two-particle correlated exciton state formed by the Coulomb interaction between single-particle holes and electrons. We find that the ultrafast transfer of an exciton's hole across a type II band-aligned semiconductor heterostructure leads to an unexpected sub-200-femtosecond upshift of the single-particle energy of the electron being photoemitted from the two-particle exciton state. While energy relaxation usually leads to an energetic downshift of the spectroscopic signature, we show that this upshift is a clear fingerprint of the correlated interaction of the electron and hole parts of the exciton. In this way, time-resolved photoelectron spectroscopy is straightforwardly established as a powerful method to access electron-hole correlations and cooperative behavior in quantum materials. Our work highlights this capability and motivates the future study of optically inaccessible correlated excitonic and electronic states of matter.

Moiré superlattices in atomically thin van der Waals heterostructures hold great promise for extended control of electronic and valleytronic lifetimes 1-7 , the confinement of excitons in artificial moiré lattices 8-13 and the formation of exotic quantum phases 14-18 . Such moiré-induced emergent phenomena are particularly strong for interlayer excitons, where the hole and the electron are localized in different layers of the heterostructure 19,20 . To exploit the full potential of correlated moiré and exciton physics, a thorough understanding of the ultrafast interlayer exciton formation process and the real-space wavefunction confinement is indispensable. Here we show that femtosecond photoemission momentum microscopy provides quantitative access to these key properties of the moiré interlayer excitons. First, we elucidate that interlayer excitons are dominantly formed through femtosecond exciton-phonon scattering and subsequent charge transfer at the interlayer-hybridized Σ valleys. Second, we show that interlayer excitons exhibit a momentum fingerprint that is a direct hallmark of the superlattice moiré modification. Third, we reconstruct the wavefunction distribution of the electronic part of the exciton and compare the size with the real-space moiré superlattice. Our work provides direct access to interlayer exciton formation dynamics in space and time and reveals opportunities to study correlated moiré and exciton physics for the future realization of exotic quantum phases of matter., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Comprehending far-from-equilibrium many-body interactions is one of the major goals of current ultrafast condensed matter physics research. Here, a particularly interesting but barely understood situation occurs during a strong optical excitation, where the electron and phonon systems can be significantly perturbed and the quasiparticle distributions cannot be described with equilibrium functions. In this work, we use time- and angle-resolved photoelectron spectroscopy to study such far-from-equilibrium many-body interactions for the prototypical material graphene. In accordance with theoretical simulations, we find remarkable transient renormalizations of the quasiparticle self-energy caused by the photoinduced nonequilibrium conditions. These observations can be understood by ultrafast scatterings between nonequilibrium electrons and strongly coupled optical phonons, which signify the crucial role of ultrafast nonequilibrium dynamics on many-body interactions. Our results advance the understanding of many-body physics in extreme conditions, which is important for any endeavor to optically manipulate or create non-equilibrium states of matter.

We present a novel setup to measure the transverse magneto-optical Kerr effect in the extreme ultraviolet spectral range based on a fiber laser amplifier system with a repetition rate between 100 and 300 kHz, which we use to measure element-resolved demagnetization dynamics. The setup is equipped with a strong electromagnet and a cryostat, allowing measurements between 10 and 420 K using magnetic fields up to 0.86 T. The performance of our setup is demonstrated by a set of temperature- and time-dependent magnetization measurements with elemental resolution.

Background: Inpatient CT-guided core needle biopsies are an integral diagnostic method to obtain a histology from lesions of unknown dignity in oncology. The purpose of this study was to evaluate feasibility, sensitivity, specificity, and complication rate of diagnostic CT-guided percutaneous core needle biopsies in oncology outpatients., Patients and Methods: We retrospectively analyzed data of all oncology outpatients who received CT-guided core needle biopsies between August 2001 and March 2005., Results: 432 outpatients received 465 CT-guided core needle biopsies using a 14-, 16-, or 18-gauge coaxial cutting needle. 174 patients (37%) were biopsied for intra-abdominal lesions, 130 (28%) for intrathoracic lesions, 55 (12%) for bone lesions, 40 (9%) for peripheral tumors, 36 (8%) for peripheral lymph nodes, and 30 (7%) for central lymph nodes. 249 (53%) biopsies were performed in local anesthesia, 216 (47%) in general anesthesia. Sensitivity was 94%, specificity 92%, and effective accuracy 92%. Complications occurred after 23 biopsies (4.9%). A pneumothorax occurred after 17 thorax biopsies (13%). 7 patients (1.5%) had to be hospitalized after the biopsy. No patient died due to the procedure., Conclusion: CT-guided core needle biopsies are feasible and safe in oncology outpatients. The technique shows a high diagnostic sensitivity and specificity with a low complication rate in routine care., (Copyright (c) 2009 S. Karger AG, Basel.)

The national breast cancer screening programme in Luxembourg, the Mammography Programme (MP), was launched in 1992. Its primary goal was to set up an organised breast cancer screening with biennial invitation-reinvitation of women 50-64 years, 2-view mammography, technical quality assurance, double-reading procedures and close monitoring of performance. In 1994, the decision was taken by health authorities to only reimburse screening mammograms done within the MP. We evaluated the performance of 3 screening rounds that took place in 1992-1997. In 1992, 4,815 women had opportunistic screening and 4,790 attended the MP. In 1997, 861 women had opportunistic screening and 8,603 attended the MP. In 1997, the participation rate in the MP reached 50%. The referral rate in the MP was 10% for initial screening and 5% for subsequent screening. Echographic examinations accounted for 71% of referrals. Per 1,000 screened women, biopsy and cancer rates were 18.0 and 8.0 for initial screening and 10.3 and 5.8 for subsequent screening. Twenty-one percent of the breast cancers diagnosed in screened women were interval cancers. The age-adjusted proportion of tumours >20 mm was 56.1% before 1992, 45.1% for women not (yet) screened by the MP, 27.0% for interval cancers, 26.6% for initial screening and 12.0% for subsequent screenings. Tumour size distribution was similar to that observed in the Dutch Breast Cancer Screening Programme, 1990-1993, except that in the latter programme, no difference was observed between initial and subsequent screening. The Luxembourg experience shows that in a liberal health care system, a policy of organising the screening process by reimbursing only those mammograms done within the context of the organised screening programme can drastically reduce opportunistic screening. Further efforts in the Mammography Programme will aim at increasing participation and look at ways to decrease referrals to echography., (Copyright 2001 Wiley-Liss, Inc.)