Hybridization and crystal-field effects in Kondo insulators studied by means of core-level spectroscopy

The physics of heavy-fermion materials is governed by the hybridization between itinerant conduction electrons and localized f electrons (c-f hybridization). At low temperatures the Kondo effect leads to the emergence of heavy quasiparticles with a huge effective mass that can be up to 1000 times larger than the bare electron mass, giving the class of heavy fermions their name. The screening of the localized magnetic moments by the conduction electrons due to the Kondo effect competes with the indirect Ruderman-Kittel-Kasuya-Yoshida exchange, which also has its origin in the hybridization interaction and wants to drive the system into a magnetically ordered ground state. Heavy fermions are regarded as dense Kondo lattice systems, in which the balance between the two interactions is of crucial importance for the ground-state properties. Valence fluctuations, Kondo insulating and semiconducting behavior, spin and charge gaps, unconventional superconductivity, quantum criticality and non-Fermi liquid behavior are observed in these materials, with remarkable consequences for magnetic, thermodynamic and electronic properties at low temperatures. ----- This thesis is mainly focused on the class of Kondo insulators, which also comprises Kondo semiconductors and semimetals. When the right conditions are met -- i.e. for a certain number of electrons per unit cell and for certain symmetries of the electronic structure -- the interaction between the conduction and f electrons opens a narrow hybridization gap close to the Fermi level. The (anisotropic) hybridization gap is found to be responsible for many anomalous properties of Kondo insulators and several theoretical studies point out the importance of the crystalline electric field (CEF) ground-state symmetry for the gap formation. ----- Here we investigate the Kondo semiconductor CeNiSn, as well as the CeM2Al10 compound family with M = Ru, Os and Fe. CeNiSn has an orthorhombic crystal structure, is one of the first narrow-gap Kondo semiconductors and has been intensively studied in the past. Many explanations for the low-temperature behavior have been suggested, all of which stress the significance of the 4f CEF ground state, which will be investigated in the framework of this thesis. The CeM2Al10 compounds belong to a fairly new class of cerium Kondo semiconductors. They also crystallize in an orthorhombic structure and order antiferromagnetically in the case of M = Ru and Os with the ordered moments being small and not aligned along the easy magnetic axis. In combination with the unexpectedly high ordering temperatures of T_N = 27K (Ru) and 29K (Os), the magnetic order is of rather unusual character. The physical properties show large anisotropies and presence of c-f hybridization despite the high ordering temperatures. We therefore determine the CEF wave functions in this compound family and quantify the degree of c-f hybridization in order to address speculations about the impact of hybridization on the magnetic order. In addition, on the search for parameters which correlate with ground-state properties in heavy-fermion compounds, we investigate the CEF ground states of the intermetallic substitution series CeRh(1-x)Ir(x)In5 since its phase diagram covers all phases of interest, from antiferromagnetic to superconducting as well as regions of phase coexistence. ----- To shed light on the issues above, namely the CEF ground state and the hybridization strength, respectively, two new experimental approaches are used: polarization-dependent x-ray absorption spectroscopy (XAS) and hard x-ray photoelectron spectroscopy (HAXPES). Commonly, the CEF is investigated by inelastic neutron scattering, however, in Kondo insulators a substantial broadening of the CEF excitations and the existence of spin gaps prevent the access to the CEF. Recently, linearly polarized XAS at the Ce M_(4,5) edge has been proven to be highly useful when it comes to the determination of the 4f ground-state wave function in tetragonal rare earth systems (and also in cubic compounds under the influence of an external magnetic field). In the present thesis the same technique is applied to the above-mentioned materials, demonstrating that linearly polarized XAS can be employed to obtain an unambiguous and reliable picture of the CEF ground state even in Kondo-insulating systems and even for symmetries lower than tetragonal. In addition to that, HAXPES measurements on the CeM2Al10 series are presented. A common technique for studying hybridization effects in rare earths, and their electronic structure in general, is photoelectron spectroscopy in the soft x-ray range (hv <= 1.5keV). However, in this energy region surface effects are known to matter so that the picture about the hybridization interaction might be distorted with respect to the bulk. The use of hard x-rays (hv = 5-10keV) guarantees a sufficiently large probing depth for obtaining information about the actual bulk electronic structure. In a detailed quantitative analysis of HAXPES $3d$ core level spectra -- using a combination of full multiplet calculations and a configuration interaction model (fm-CI model) -- the hybridization strength can be quantified. ----- The XAS results show that the CEF ground states of CeRu2Al10 and CeOs2Al are very similar, while it is clearly different for the non-ordering system CeFe2Al10. The CEF description nicely explains the magnetic anisotropy observed in susceptibility data and to a large extent the small ordered moments along the c axis. We provide a reliable quantitative description of the CEF ground state of the CeM2Al10 compounds which now serves as input for further studies. Furthermore, the analysis of the HAXPES data in the fm-CI model allows to quantify the intermediate 4f valence and establishes that the exchange interaction increases within the series from Ru to Os to Fe. A substantial amount of Kondo screening is shown to be present even in the magnetically ordered Ru and Os compounds. ----- The polarized XAS study on CeNiSn demonstrates that the monoclinic CEF is well described in a trigonal approximation, and the determined 4f ground-state wave function is consistent with results from inelastic neutron scattering for Cu-doped CeNiSn. Thanks to this first successful direct experimental detection of the 4f ground state in CeNiSn, an important step is made towards a better understanding of the mechanism behind the gap formation in this archetype Kondo insulator. ----- Moreover, the systematic investigation of the CeRh(1-x)Ir(x)In5 substitution series by means of polarization-dependent XAS for the first time reveals a correlation between the CEF anisotropy and the formation of an antiferromagnetic, superconducting or coexisting (antiferromagnetism plus superconductivity) ground state. This discovery shows that the anisotropy of the 4f ground-state wave function is a good predictor for when these materials are magnetic or superconducting

How cold is Dark Matter? Constraints from Milky Way Satellites

We test the luminosity function of Milky Way satellites as a constraint for the nature of Dark Matter particles. We perform dissipationless high-resolution N-body simulations of the evolution of Galaxy-sized halo in the standard Cold Dark Matter (CDM) model and in four Warm Dark Matter (WDM) scenarios, with a different choice for the WDM particle mass (m_w). We then combine the results of the numerical simulations with semi-analytic models for galaxy formation, to infer the properties of the satellite population. Quite surprisingly we find that even WDM models with relatively low m_w values (2-5 keV) are able to reproduce the observed abundance of ultra faint (Mv<-9) dwarf galaxies, as well as the observed relation between Luminosity and mass within 300 pc. Our results suggest a lower limit of 1 keV for thermal warm dark matter, in broad agreement with previous results from other astrophysical observations like Lyman-alpha forest and gravitational lensing.Comment: 6 pages, 5 figures. Introduction improved, references added. Accepted for publication on MNRAS Letter

Attribute zur gesamtheitlichen Charakterisierung der Wahrnehmung von Straßenverkehrsgeräuschen

Die Lärmwirkungsforschung beschäftigt sich bereits seit vielen Jahren mit der Belastung durch Verkehrsgeräusche und den dadurch hervorgerufenen extra-auralen Lärmwirkungen einschließlich der Lärmbelästigung. Dabei wird die Belästigung üblicherweise in den Zusammenhang zum gemittelten Schalldruckpegel (z.B. LAeq, LDEN) der unerwünschten Geräuschquelle gestellt und Dosis-Wirkungsrelationen abgeleitet. Die Wirkung wird demnach nahezu ausschließlich mit dem Grad der Belästigung beschrieben und eine differenzierte Betrachtung der verschiedenen Aspekte der Geräuschwahrnehmung erfolgt nich

PSMA PET for the Evaluation of Liver Metastases in Castration-Resistant Prostate Cancer Patients: A Multicenter Retrospective Study

Simple Summary Visceral involvement in prostate cancer (PCa) represents a negative prognostic factor. Liver metastases typically occur in systemic, late-stage, castration-resistant prostate cancer (CRPC). The diagnostic performance of [68Ga]Ga-PSMA-11-PET for visceral metastases of CRPC patients has never been systematically assessed. Our aim was to evaluate the diagnostic performance of PSMA-PET compared to conventional imaging, i.e., CT or MRI, or liver biopsy in the detection of liver metastases in CRPC patients. The secondary aim was to assess the ability of radiomics to predict the presence of liver metastases. Regarding liver metastases assessment in CRPC patients, [68Ga]-PSMA-11-PET demonstrated moderate sensitivity while high specificity, positive predictive value, and reproducibility compared to conventional imaging and liver biopsy. However, nuclear medicine physicians should carefully assess the liver parenchyma on PET images, especially in patients at higher risk for liver metastases and with high PSA values. Moreover, radiomic features may aid in recognizing higher-risk patients to develop them. Background: To evaluate the diagnostic performance of PSMA-PET compared to conventional imaging/liver biopsy in the detection of liver metastases in CRPC patients. Moreover, we evaluated a PSMA-PET/CT-based radiomic model able to identify liver metastases. Methods: Multicenter retrospective study enrolling patients with the following inclusion criteria: (a) proven CRPC patients, (b) PSMA-PET and conventional imaging/liver biopsy performed in a 6 months timeframe, (c) no therapy changes between PSMA-PET and conventional imaging/liver biopsy. PSMA-PET sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy for liver metastases were calculated. After the extraction of radiomic features, a prediction model for liver metastases identification was developed. Results: Sixty CRPC patients were enrolled. Within 6 months before or after PSMA-PET, conventional imaging and liver biopsy identified 24/60 (40%) patients with liver metastases. PSMA-PET sensitivity, specificity, PPV, NPV, and accuracy for liver metastases were 0.58, 0.92, 0.82, 0.77, and 0.78, respectively. Either number of liver metastases and the maximum lesion diameter were significantly associated with the presence of a positive PSMA-PET (p &lt; 0.05). On multivariate regression analysis, the radiomic feature-based model combining sphericity, and the moment of inverse difference (Idm), had an AUC of 0.807 (95% CI:0.686-0.920). Conclusion: For liver metastases assessment, [68Ga]Ga-PSMA-11-PET demonstrated moderate sensitivity while high specificity, PPV, and inter-reader agreement compared to conventional imaging/liver biopsy in CRPC patients

Adaptive Individualized high-dose preoperAtive (AIDA) chemoradiation in high-risk rectal cancer: a phase II trial

Purpose To evaluate the pathological complete response (pCR) rate of locally advanced rectal cancer (LARC) after adaptive high-dose neoadjuvant chemoradiation (CRT) based on (18) F-fluorodeoxyglucose positron emission tomography/computed tomography ((18) F-FDG-PET/CT).Methods The primary endpoint was the pCR rate. Secondary endpoints were the predictive value of (18) F-FDG-PET/CT on pathological response and acute and late toxicity. All patients performed (18) F-FDG-PET/CT at baseline (PET0) and after 2 weeks during CRT (PET1). The metabolic PET parameters were calculated both at the PET0 and PET1. The total CRT dose was 45 Gy to the pelvic lymph nodes and 50 Gy to the primary tumor, corresponding mesorectum, and to metastatic lymph nodes. Furthermore, a sequential boost was delivered to a biological target volume defined by PET1 with an additional dose of 5 Gy in 2 fractions. Capecitabine (825 mg/m(2) twice daily orally) was prescribed for the entire treatment duration.Results Eighteen patients (13 males, 5 females; median age 55 years [range, 41-77 years]) were enrolled in the trial. Patients underwent surgical resection at 8-9 weeks after the end of neoadjuvant CRT. No patient showed grade &gt; 1 acute radiation-induced toxicity. Seven patients (38.8%) had TRG = 0 (complete regression), 5 (27.0%) showed TRG = 2, and 6 (33.0%) had TRG = 3. Based on the TRG results, patients were classified in two groups: TRG = 0 (pCR) and TRG = 1, 2, 3 (non pCR). Accepting p &lt; 0.05 as the level of significance, at the Kruskal-Wallis test, the medians of baseline-MTV, interim-SUVmax, interim-SUVmean, interim-MTV, interim-TLG, and the MTV reduction were significantly different between the two groups. (18) F-FDG-PET/CT was able to predict the pCR in 77.8% of cases through compared evaluation of both baseline PET/CT and interim PET/CT.Conclusions Our results showed that a dose escalation on a reduced target in the final phase of CRT is well tolerated and able to provide a high pCR rate

Automated Prediction of the Response to Neoadjuvant Chemoradiotherapy in Patients Affected by Rectal Cancer

Simple Summary Colorectal cancer is the second most malignant tumor per number of deaths after lung cancer and the third per number of new cases after breast and lung cancer. The correct and rapid identification (i.e., segmentation of the cancer regions) is a fundamental task for correct patient diagnosis. In this study, we propose a novel automated pipeline for the segmentation of MRI scans of patients with LARC in order to predict the response to nCRT using radiomic features. This study involved the retrospective analysis of T-2-weighted MRI scans of 43 patients affected by LARC. The segmentation of tumor areas was on par or better than the state-of-the-art results, but required smaller sample sizes. The analysis of radiomic features allowed us to predict the TRG score, which agreed with the state-of-the-art results. Background: Rectal cancer is a malignant neoplasm of the large intestine resulting from the uncontrolled proliferation of the rectal tract. Predicting the pathologic response of neoadjuvant chemoradiotherapy at an MRI primary staging scan in patients affected by locally advanced rectal cancer (LARC) could lead to significant improvement in the survival and quality of life of the patients. In this study, the possibility of automatizing this estimation from a primary staging MRI scan, using a fully automated artificial intelligence-based model for the segmentation and consequent characterization of the tumor areas using radiomic features was evaluated. The TRG score was used to evaluate the clinical outcome. Methods: Forty-three patients under treatment in the IRCCS Sant'Orsola-Malpighi Polyclinic were retrospectively selected for the study; a U-Net model was trained for the automated segmentation of the tumor areas; the radiomic features were collected and used to predict the tumor regression grade (TRG) score. Results: The segmentation of tumor areas outperformed the state-of-the-art results in terms of the Dice score coefficient or was comparable to them but with the advantage of considering mucinous cases. Analysis of the radiomic features extracted from the lesion areas allowed us to predict the TRG score, with the results agreeing with the state-of-the-art results. Conclusions: The results obtained regarding TRG prediction using the proposed fully automated pipeline prove its possible usage as a viable decision support system for radiologists in clinical practice

Luminosity function and radial distribution of Milky Way Satellites in a LCDM Universe

We study the luminosity function and the radial distribution of satellite galaxies within Milky Way sized haloes as predicted in Cold Dark Matter based models of galaxy formation, making use of numerical N-body techniques as well as three different semi-analytic model (SAMs) galaxy formation codes. We extract merger trees from very high-resolution dissipationless simulations of four Galaxy-sized DM haloes, and use these as common input for the semi-analytic models. We present a detailed comparison of our predictions with the observational data recently obtained on the Milky Way satellite luminosity function (LF). We find that semi-analytic models with rather standard astrophysical ingredients are able to reproduce the observed luminosity function over six orders of magnitude in luminosity, down to magnitudes as faint as M_V=-2. We also perform a comparison with the actual observed number of satellites as a function of luminosity, by applying the selection criteria of the SDSS survey to our simulations instead of correcting the observations for incompleteness. Using this approach we again find good agreement for both the luminosity and radial distributions of MW satellites. We investigate which physical processes in our models are responsible for shaping the predicted satellite LF, and find that tidal destruction, suppression of gas infall by a photo-ionizing background, and supernova feedback all make important contributions. We conclude that the number and luminosity of Milky Way satellites can be naturally accounted for within the (Lambda) Cold Dark Matter paradigm, and this should no longer be considered a problem.Comment: 16 pages, 15 figures, paper shortened, statistical analysis improved, new title, accepted for publication in MNRA

CeRu4Sn6: A strongly correlated material with nontrivial topology

Topological insulators form a novel state of matter that provides new opportunities to create unique quantum phenomena. While the materials used so far are based on semiconductors, recent theoretical studies predict that also strongly correlated systems can show non-trivial topological properties, thereby allowing even the emergence of surface phenomena that are not possible with topological band insulators. From a practical point of view, it is also expected that strong correlations will reduce the disturbing impact of defects or impurities, and at the same increase the Fermi velocities of the topological surface states. The challenge is now to discover such correlated materials. Here, using advanced x-ray spectroscopies in combination with band structure calculations, we infer that CeRu4Sn6 is a strongly correlated material with non-trivial topology

Calculation of weather-corrected traffic noise immission levels on the basis of emission data and meteorological quantities

The assessment methods for noise exposure from different modes of traffic are usually based on simplified models. Regarding meteorological influences, it is well known that weather conditions in favor of sound propagation can cause maximum noise levels which are not reflected in the averaged rating levels. Especially in larger distances from the emitter these effects become evident. Correction factors are not always sufficient to capture the strong impact of the actual atmospheric structure. An applicable and accurate meteorological model for obtaining the “real” immission load in residential areas can serve e.g. as a supplement to the averaged rating levels to better understand noise situation. In this study we look at the sound propagation models NMPB-Roads-2008 and Harmonoise, which include meteorological considerations. We compare them to the German RLS-90, discuss their advantages and drawbacks, and apply them to a simple weather-dependent test scenario to examine if their meteorologically corrected noise immission levels are feasible

Effectiveness of noise barrier add-on elements

Lärmschutzwandaufsätze bieten eine einfache Möglichkeit zur Verbesserung der akustischen Wirksamkeit bestehender Lärmschutzwände. Hierbei ergibt sich zum einen eine höhere Pegelminderung aufgrund der Erhöhung der Wand, zum anderen lassen sich durch spezielle Geometrien oder absorbierende Materialien zusätzliche Einfügedämpfungen generieren. Am Beispiel eines Lärmspoilers aus Flüsterschaum wurde die durch den Aufsatz erzeugte Pegelminderung untersucht und einer äquivalenten Erhöhung der Lärmschutzwand gegenübergestellt. Hierfür wurde auf Modellmessungen in der Halle für akustische Modelltechnik, Freifeldmessungen im Nah- und Fernfeld sowie auf numerische Simulationen der Schallausbreitung über die Aufsatzelemente zurückgegriffen. Darüber hinaus ist auch die Hitze-, Frost- und UV-Beständigkeit des Aufsatzmaterials Gegenstand des vorliegenden Projektes. Die Untersuchung der Materialproben im Impedanz-Messrohr nach Materialbelastung ergibt, dass die akustischen Eigenschaften größtenteils erhalten bleiben. Es ist keine signifikante Abschwächung des Absorptionsgrades zu beobachten. Hinsichtlich der akustischen Wirksamkeit zeigt sich, dass die betrachteten Lärmschutzwandaufsätze im Vergleich zu einer Erhöhung der Wand keinen signifikanten akustischen Mehrwert besitzen. Alle Messungen liefern bei normgerechten Vorgehen eine akustische Wirksamkeit von unter 1 dB. Verglichen mit der (niedrigeren) Wand ohne Aufsatz führt die Installation der Lärmspoiler zu Pegelminderungen von ca. 3 dB – 4 dB. Die numerischen Simulationen bestätigen die Messergebnisse im Wesentlichen. In weiterführenden Vergleichen lassen sich zudem die verschiedenen Einflüsse auf die Schallausbreitung separieren: Während das Absorptionsmaterial selbst einen positiven Effekt auf die akustische Wirksamkeit hat, scheint die Geometrie des Aufsatzes den erreichbaren Einfügedämpfungen abträglich zu sein. Die Untersuchung zeigt, dass die Modifizierung der Beugungskante prinzipiell Potential für einen zusätzlichen Minderungseffekt birgt. Die methodenübergreifende Analyse erlaubt eine gute Einschätzung der akustischen Wirksamkeit und soll zukünftig bei der Optimierung und praktischen Umsetzung derartiger Aufsätze helfen.Add-on elements for noise barriers offer an easy possibility to improve the acoustic efficiency of existing barriers. Using such elements leads to an additional sound level reduction due to the increased height of the barrier, on the other hand special geometries or absorbing materials allow generating enhanced insertion losses. In the framework of this study the level reduction induced by a so-called “noise spoiler” made of synthetic foam was determined and compared to the effect obtained by simply increasing the barrier height accordingly. For this purpose, model measurements in the acoustic laboratory, field measurements in the near and far field and numeric simulations of the sound propagation across the modified edge were carried out. Moreover, the durability of the absorber material against heat, cold and UV radiation is assessed. The material test with the impedance measuring tube after exposure to heat, cold and UV radiation reveals that the acoustic properties are largely preserved. No significant decrease of the degree of absorption can be detected. Regarding the acoustic efficiency the measurements illustrate that the considered add-on elements have no significant acoustic benefit compared to an equivalent elevation of the noise barrier. Values below 1 dB for the acoustic efficiency are obtained when the measurements are carried out according to the standards. When comparing the results to the case of a (lower) barrier without add-on, the installation of the “noise spoiler” yields a sound level reduction of about 3 dB – 4 dB. The numeric simulations essentially confirm the measurement results. Further analyses additionally allow separating the different influences on the sound propagation: While the absorber material itself has a positive impact on the acoustic efficiency, the geometry of the add-on elements seems to be detrimental for the achievable insertion losses. The investigation shows that, in principle, the modification of the diffraction edge has the potential for additional noise reduction. The multi-methodological evaluation allows a fair evaluation of the acoustic efficiency and will serve as valuable input for future optimization and realization processes