Low-threshold power and tunable integrated optical limiter based on an ultracompact VO2/Si waveguide

status: publishe

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Growth and characterization of ferroelectric LaTiO₃.₅ thin films

Depending upon the oxygen content x, LaTiO3+x can be a semiconductor, a metal, or a ferroelectric at room temperature. Using a thin-film approach, it is in principle possible to adjust the oxygen content in the growth direction and thus tune the electronic properties within the same sample. We report here on a systematic study of the epitaxial growth of LaTiO3.5 films on SrTiO3 (110) substrates using molecular beam epitaxy. The epitaxial behaviour and the growth mechanism of these films have been investigated by means of X-ray diffraction, transmission electron microscopy, and in situ reflection high-energy electron diffraction analysis.status: publishe

Electric-field-driven Mott metal-insulator transition in correlated thin films: An inhomogeneous dynamical mean-field theory approach

Simulations are carried out based on the dynamical mean-field theory (DMFT) in order to investigate the properties of correlated thin films for various values of the chemical potential, temperature, interaction strength, and applied transverse electric field. Application of a sufficiently strong field to a thin film at half filling leads to the appearance of conducting regions near the surfaces of the film, whereas in doped slabs the application of a field leads to a conductivity enhancement on one side of the film and a gradual transition to the insulating state on the opposite side. In addition to the inhomogeneous DMFT, a local density approximation (LDA) is considered in which the particle density n, quasiparticle residue Z, and spectral weight at the Fermi level A(omega = 0) of each layer are approximated by a homogeneous bulk environment. A systematic comparison between the two approaches reveals that the less expensive LDA results are in good agreement with the DMFT approach, except close to the metal-to-insulator transition points and in the layers immediately at the film surfaces. LDA values for n are overall more reliable than those for Z and A(omega = 0). The hysteretic behavior (memory effect) characteristic of the bulk doping driven Mott transition persists in the slab.10 pages, 11 figuresstatus: publishe

Antiferromagnetic LaFeO₃ thin films and their effect on exchange bias

Antiferromagnetic (AFM) orthoferrites are interesting model systems for exploring the correlation between their crystalline and AFM domains and the resulting exchange bias when coupled to a ferromagnetic layer. In particular, LaFeO₃ (LFO) has a Neel temperature, T(N) = 740 K, which is the highest in the orthoferrite family. The recent developments of synchrotron radiation-based photoelectron emission microscopy (PEEM) have provided the possibility of studying AFM domain structures as well as the magnetic coupling between the AFM and the adjacent ferromagnetic (FM) layer, domain by domain. Thin films of LFO have proved excellent candidates for such studies because their AFM domains are well defined and large enough to be readily imaged by PEEM. This paper reviews the growth, structural and magnetic properties of LFO thin films as well as exchange coupling to a FM layer. The strong correlation between structural and AFM domains in this material allows us to investigate the exchange coupling as a function of the domain configuration, which can be changed by using different substrate material and substrate orientation. A significant increase of the exchange bias field by a factor of about 10 was obtained when LFO was diluted with Ni atoms in the volume part. In this sample, the structural domain boundary became corrugated due to substitutional defects. Our results indicate that the details of the precise domain boundary configuration strongly affect the exchange coupling.status: publishe

Synthesis and Properties of Gold Nanoparticle Arrays Self-Organized on Surface-Deposited Lysozyme Amyloid Scaffolds

© 2014 American Chemical Society. In this study, amyloid fibers prepared from hen egg white lysozyme (HEWL) are specifically mediating the assembly of citrate-capped gold nanoparticles, on glass and silicon substrates. The organization of nanoparticles is investigated for nanoparticle diameters of 5, 15, and 25 nm, using variable deposition times, and under a range of pH, salt, citric acid and nanoparticle concentrations. The observed periodic self-organization of nanoparticles is mainly influenced by the interparticle interactions rather than by the spacing of binding groups at the surface of the amyloid fiber template. For a fixed ionic strength of 2.3 mM and particle concentration, the interparticle distance increases with the nanoparticle diameter in agreement with the values predicted by the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. UV-visible spectroscopy measurements show a red shift of the 520 nm plasmon absorption peak associated with spherical gold nanoparticles up to 650 nm upon aggregation or decrease in the interparticle distance. Such protein templates deposited on technologically relevant surfaces allow the self-assembly of inorganic nanoparticle arrays with functional optoelectronic properties.status: publishe

Osteoporosis in Frail Patients: A Consensus Paper of the Belgian Bone Club.

In this consensus paper, the Belgian Bone Club aims to provide a state of the art on the epidemiology, diagnosis, and management of osteoporosis in frail individuals, including patients with anorexia nervosa, patients on dialysis, cancer patients, persons with sarcopenia, and the oldest old. All these conditions may indeed induce bone loss that is superimposed on physiological bone loss and often remains under-recognized and under-treated. This is of particular concern because of the major burden of osteoporotic fractures in terms of morbidity, mortality, and economic cost. Therefore, there is an urgent need to appreciate bone loss associated with these conditions, as this may improve diagnosis and management of bone loss and fracture risk in clinical practice

Electric Field-Induced Oxidation of Ferromagnetic/Ferroelectric Interfaces

Composite multiferroics are a new class of material where magneto-electric coupling is achieved by creating an interface between a ferromagnetic and a ferroelectric compound. The challenge of understanding the chemical and magnetic properties of such interface is a key to achieve good magneto-electric coupling. The unique possibilities offered by isotope sensitive techniques are used to selectively investigate the interface's chemistry and magnetism in Fe/BaTiO3 and Fe/LiNbO3 systems during the application of an electric field. With a large enough electric field, a strong oxidation of Fe is triggered, which creates a magnetically dead interface. This leads to an irreversible decrease of the magneto-electric coupling properties. Material parameters are identified that determine under which electric field the interface may be modified. The results are confirmed on the two systems and are expected to be widespread in this new class of hybrid material. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.status: publishe