Phonons in intrinsic Josephson systems with parallel magnetic field

Subgap resonances in the I-V curves of layered superconductors are explained by the coupling between Josephson oscillations and phonons with dispersion in c-direction. In the presence of a magnetic field applied parallel to the layers additional structures due to fluxon motion appear. Their coupling with phonons is investigated theoretically and a shift of the phonon resonances in strong magnetic fields is predicted.Comment: Invited Paper to the "2nd International Symposium on Intrinsic Josephson Effects and Plasma Oscillations in High-Tc Superconductors", 22-24 August 2000, Sendai, Japan, to be published in Physica

Wild clocks: preface and glossary

No abstract available

Electronic compressibility and charge imbalance relaxation in cuprate superconductors

In the material SmLa$_{1-x}$Sr$_x$CuO$_{4-\delta}$ with alternating intrinsic Josephson junctions we explain theoretically the relative amplitude of the two plasma peaks in transmission by taking into account the spatial dispersion of the Josephson Plasma Resonance in $c$ direction due to charge coupling. From this and the magnetic field dependence of the plasma peaks in the vortex solid and liquid states it is shown that the electronic compressibility of the CuO$_2$ layers is consistent with a free electron value. Also the London penetration depth $\lambda_{ab} \approx 1100 {\rm \AA}$ near $T_c$ can be determined. The voltage response in the $IV$-curve of a Bi$_2$Sr$_2$CaCu$_2$O$_8$ mesa due to microwave irradiation or current injection in a second mesa is related to the nonequilibrium charge imbalance of quasiparticles and Cooper pairs and from our experimental data the relaxation time $\sim 100 {\rm ps}$ is obtained.Comment: 2 pages, 2 figures, phc-proc4-auth.cls, to be published in Physica C as a proceeding of M2S-HTSC Rio 200

Use of accelerometry to investigate physical activity in dogs receiving chemotherapy

Objectives: To perform a preliminary study to assess whether single-agent palliative or adjuvant chemotherapy has an impact on objectively measured physical activity in dogs. Methods: Fifteen dogs with neoplasia (treatment group) wore ActiGraph™ accelerometers for 5-day periods before, during and after receiving single-agent adjuvant or palliative chemotherapy. Mean 5-day total physical activity and time spent in three different intensities of activity (sedentary, light-moderate and vigorous) before, during and after receiving chemotherapy were compared to a group of 15 healthy dogs (control group). Results were also compared within the treatment group across time. Results: Prior to chemotherapy, treated dogs tended to be less active than control dogs. Treatment group dogs were slightly more active at restaging than they were prior to treatment but had similar activity levels to control dogs. Marked effects of chemotherapy on physical activity were not detected. Physical activity was slightly lower in treated dogs during chemotherapy when compared to control dogs but there was a slight increase in physical activity of treated dogs during chemotherapy when compared with pretreatment recordings. There was little change in the mean 5-day total physical activity between treated dogs during chemotherapy and at restaging but a mild decrease in time spent sedentary and increase in time spent in light-moderate activity at this comparison of time points. Clinical Significance: Single-agent adjuvant or palliative chemotherapy had minimal impact on physical activity levels in dogs with neoplasia

Magnetism in Graphene Induced by Single-Atom Defects

We study from first principles the magnetism in graphene induced by single carbon atom defects. For two types of defects considered in our study, the hydrogen chemisorption defect and the vacancy defect, the itinerant magnetism due to the defect-induced extended states has been observed. Calculated magnetic moments are equal to 1 $\mu_B$ per hydrogen chemisorption defect and 1.12$-$1.53 $\mu_B$ per vacancy defect depending on the defect concentration. The coupling between the magnetic moments is either ferromagnetic or antiferromagnetic, depending on whether the defects correspond to the same or to different hexagonal sublattices of the graphene lattice, respectively. The relevance of itinerant magnetism in graphene to the high-$T_C$ magnetic ordering is discussed.Comment: 5 pages, 6 figure

Optical Properties of Crystals with Spatial Dispersion: Josephson Plasma Resonance in Layered Superconductors

We derive the transmission coefficient, $T(\omega)$, for grazing incidence of crystals with spatial dispersion accounting for the excitation of multiple modes with different wave vectors ${\bf k}$ for a given frequency $\omega$. The generalization of the Fresnel formulas contains the refraction indices of these modes as determined by the dielectric function $\epsilon(\omega,{\bf k})$. Near frequencies $\omega_e$, where the group velocity vanishes, $T(\omega)$ depends also on an additional parameter determined by the crystal microstructure. The transmission $T$ is significantly suppressed, if one of the excited modes is decaying into the crystal. We derive these features microscopically for the Josephson plasma resonance in layered superconductors.Comment: 4 pages, 2 figures, epl.cls style file, minor change

Subgap structures in the current-voltage characteristic of the intrinsic Josephson effect due to phonons

A modified RSJ-model for the coupling of intrinsic Josephson oscillations and c-axis phonons in the high-T_c superconductors Tl_2Ba_2Ca_2Cu_3O_{10+\delta} and Bi_2Sr_2CaCu_2O_{8+\delta} is deveoped. This provides a very good explanation for recently reported subgap structures in the I-V-characteristic of the c-axis transport. It turns out that the voltages of these structures coincide with the eigenfrequencies of longitudinal optical phonons, providing a new measurement technique for this quantity. The significantly enhanced microwave emission at the subgap structures in both the GHz and THz region is discussed.Comment: correction of minor misprints, revtex, 3 pages, two postscript figures, aps, epsf, Contributed Paper to the "International Symposion on the Intrinsic Josphson effect and THz Plasma Oscillations", 22-25 February 1997, Sendai, Japan; to be published in Physica

Reflectivity and Microwave Absorption in Crystals with Alternating Intrinsic Josephson Junctions

We compute the frequency and magnetic field dependencies of the reflectivity $R(\omega)$ in layered superconductors with two alternating intrinsic Josephson junctions with different critical current densities and quasiparticle conductivities for the electric field polarized along the c-axis. The parameter $\alpha$ describing the electronic compressibility of the layers and the charge coupling of neighboring junctions was extracted for the SmLa$_{1-x}$Sr$_{x}$CuO$_{4-\delta}$ superconductor from two independent optical measurements, the fit of the loss function $L(\omega)$ at zero magnetic field and the magnetic field dependence of the peak positions in $L(\omega)$. The experiments are consistent with a free electron value for $\alpha$ near the Josephson plasma frequencies.Comment: 4 pages, 4 postscript figures, misprints in table correcte

Annual Report 2020 - Institute of Ion Beam Physics and Materials Research

As for everybody else also for the Institute of Ion Beam Physics and Materials Research (IIM), the COVID-19 pandemic overshadowed the usual scientific life in 2020. Starting in March, home office became the preferred working environment and the typical institute life was disrupted. After a little relaxation during summer and early fall, the situation became again more serious and in early December we had to severely restrict laboratory activities and the user operation of the Ion Beam Center (IBC). For the most part of 2020, user visits were impossible and the services delivered had to be performed hands-off. This led to a significant additional work load on the IBC staff. Thank you very much for your commitment during this difficult period. By now user operation has restarted, but we are still far from business as usual. Most lessons learnt deal with video conference systems, and everybody now has extensive experience in skype, teams, webex, zoom, or any other solution available. Conferences were cancelled, workshops postponed, and seminar or colloquia talks delivered online. Since experimental work was also impeded, maybe 2020 was a good year for writing publications and applying for external funding. In total, 204 articles have been published with an average impact factor of about 7.0, which both mark an all-time high for the Institute. 13 publications from last year are highlighted in this Annual Report to illustrate the wide scientific spectrum of our institute. In addition, 20 new projects funded by EU, DFG, BMWi/AiF and SAB with a total budget of about 5.7 M€ have started. Thank you very much for making this possible. Also, in 2020 there have been a few personalia to be reported. Prof. Dr. Sibylle Gemming has left the HZDR and accepted a professor position at TU Chemnitz. Congratulations! The hence vacant position as the head of department was taken over by PD Dr. Artur Erbe by Oct. 1st. Simultaneously, the department has been renamed to “Nanoelectronics”. Dr. Alina Deac has left the institute in order to dedicate herself to new opportunities at the Dresden High Magnetic Field Laboratory. Dr. Matthias Posselt went to retirement after 36 years at the institute. We thank Matthias for his engagement and wish him all the best for the upcoming period of his life. However, also new equipment has been setup and new laboratories founded. A new 100 kV accelerator is integrated into our low energy ion nanoengineering facility and complements our ion beam technology in the lower energy regime. This setup is particularly suited to perform ion implantation into 2D materials and medium energy ion scattering (MEIS). Finally, we would like to cordially thank all partners, friends, and organizations who supported our progress in 2020. First and foremost we thank the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Minister of Science and Arts of the Free State of Saxony, and the Ministers of Education and Research, and of Economic Affairs and Energy of the Federal Government of Germany. Many partners from univer¬sities, industry and research institutes all around the world contributed essentially, and play a crucial role for the further development of the institute. Last but not least, the directors would like to thank all members of our institute for their efforts in these very special times and excellent contributions in 2020