Microstructuring YbRh2Si2 for resistance and noise measurements down to ultra-low temperatures

We acknowledge funding by the German Research Foundation (DFG) via the TRR 288 (422213477, project A03, A10 and B02) and projects KR3831/4-1 and BR 4110/1-1. This work was supported by the EU H2020 European Microkelvin Platform EMP, Grant No. 824109.The discovery of superconductivity in the quantum critical Kondo-lattice system YbRh2Si2 at an extremely low temperature of 2 mK has inspired efforts to perform high-resolution electrical resistivity measurements down to this temperature range in highly conductive materials. Here we show that control over the sample geometry by microstructuring using focused-ion-beam techniques allows to reach ultra-low temperatures and increase signal-to-noise ratios (SNRs) tenfold, without adverse effects to sample quality. In five experiments we show four-terminal sensing resistance and magnetoresistance measurements which exhibit sharp phase transitions at the Néel temperature, and Shubnikov–de-Haas (SdH) oscillations between 13 T and 18 T where we identified a new SdH frequency of 0.39 kT. The increased SNR allowed resistance fluctuation (noise) spectroscopy that would not be possible for bulk crystals, and confirmed intrinsic 1/f -type fluctuations. Under controlled strain, two thin microstructured samples exhibited a large increase of TN from 67 mK up to 188 mK while still showing clear signatures of the phase transition and SdH oscillations. Superconducting quantum interference device-based thermal noise spectroscopy measurements in a nuclear demagnetization refrigerator down to 0.95 mK, show a sharp superconducting transition at Tc=1.2 mK. These experiments demonstrate microstructuring as a powerful tool to investigate the resistance and the noise spectrum of highly conductive correlated metals over wide temperature ranges.Publisher PDFPeer reviewe

Phonon-induced dephasing of localized optical excitations

The dynamics of strongly localized optical excitations in semiconductors is studied including electron-phonon interaction. The coupled microscopic equations of motion for the interband polarization and the carrier distribution functions contain coherent and incoherent contributions. While the coherent part is solved through direct numerical integration, the incoherent one is treated by means of a generalized Monte Carlo simulation. The approach is illustrated for a simple model system. The temperature and excitation energy dependence of the optical dephasing rate is analyzed and the results are compared to those of alternative approaches

Indications and results of sternal allograft transplantation: learning from a worldwide experience

Background Reconstruction of the anterior chest wall defect after sternectomy is a challenge for cardiothoracic surgeons. In 2010 the Padua group published the first case of cadaveric sternum transplantation after sternectomy. This multi-center study reports the clinical indications, early and long-term results of sternal chondral allograft transplantation. Methods This is a retrospective multicentre-study from seven Academic-Centres. Demographic data, surgical indications, technical details, early postoperative results were collected. The complications, long-term stability and tolerance of the allografts were also analysed. Results Between January 2008 and December 2019 58-patients underwent sternectomy followed by reconstruction using cadaveric-cryopreserved sterno-chondral allografts. Thirty-two patients were males, with a median age of 63.5 years(IQR50-72). Indications for sternectomy were secondary sternal tumors(n=13), primary sternal tumors(n=15) and non-neoplastic disease(30). Thirty patients underwent total sternectomy, 16 lower-body sternectomy and 12 upper-body-manubrium resection. The 30-days mortality was 5%. The overall morbidity was 31%. Six early reoperations were necessary because of bleeding(n=1), titanium-plates dislocation(n=1) and re-suture of the skin in the lower part of the incision(n=4). Overall, the 5-year survival was 74%. The surviving patient\u2019s reconstructions are stable and free from mechanical or infective complications. Conclusions The main indications for sternal allograft implantation were complex post sternotomy dehiscence followed by primary or secondary tumor involvement of the sternum. The collected results demonstrate that sterno-chondral allograft transplantation is a safe and effective method in reconstructing the anterior chest wall after sternectomy. Further studies to demonstrate the integration of the bone grafts into the patient\u2019s sternal wall will be made

Rivaroxaban with or without aspirin in stable cardiovascular disease

BACKGROUND: We evaluated whether rivaroxaban alone or in combination with aspirin would be more effective than aspirin alone for secondary cardiovascular prevention. METHODS: In this double-blind trial, we randomly assigned 27,395 participants with stable atherosclerotic vascular disease to receive rivaroxaban (2.5 mg twice daily) plus aspirin (100 mg once daily), rivaroxaban (5 mg twice daily), or aspirin (100 mg once daily). The primary outcome was a composite of cardiovascular death, stroke, or myocardial infarction. The study was stopped for superiority of the rivaroxaban-plus-aspirin group after a mean follow-up of 23 months. RESULTS: The primary outcome occurred in fewer patients in the rivaroxaban-plus-aspirin group than in the aspirin-alone group (379 patients [4.1%] vs. 496 patients [5.4%]; hazard ratio, 0.76; 95% confidence interval [CI], 0.66 to 0.86; P<0.001; z=−4.126), but major bleeding events occurred in more patients in the rivaroxaban-plus-aspirin group (288 patients [3.1%] vs. 170 patients [1.9%]; hazard ratio, 1.70; 95% CI, 1.40 to 2.05; P<0.001). There was no significant difference in intracranial or fatal bleeding between these two groups. There were 313 deaths (3.4%) in the rivaroxaban-plus-aspirin group as compared with 378 (4.1%) in the aspirin-alone group (hazard ratio, 0.82; 95% CI, 0.71 to 0.96; P=0.01; threshold P value for significance, 0.0025). The primary outcome did not occur in significantly fewer patients in the rivaroxaban-alone group than in the aspirin-alone group, but major bleeding events occurred in more patients in the rivaroxaban-alone group. CONCLUSIONS: Among patients with stable atherosclerotic vascular disease, those assigned to rivaroxaban (2.5 mg twice daily) plus aspirin had better cardiovascular outcomes and more major bleeding events than those assigned to aspirin alone. Rivaroxaban (5 mg twice daily) alone did not result in better cardiovascular outcomes than aspirin alone and resulted in more major bleeding events