Competing correlated states around the zero-field Wigner crystallization transition of electrons in two dimensions.

The competition between kinetic energy and Coulomb interactions in electronic systems leads to complex many-body ground states with competing orders. Here we present zinc oxide-based two-dimensional electron systems as a high-mobility system to study the low-temperature phases of strongly interacting electrons. An analysis of the electronic transport provides evidence for competing correlated metallic and insulating states with varying degrees of spin polarization. Some features bear quantitative resemblance to quantum Monte Carlo simulation results, including the transition point from the paramagnetic Fermi liquid to Wigner crystal and the absence of a Stoner transition. At very low temperatures, we resolve a non-monotonic spin polarizability of electrons across the phase transition, pointing towards a low spin phase of electrons, and a two-order-of-magnitude positive magnetoresistance that is challenging to understand within traditional metallic transport paradigms. This work establishes zinc oxide as a platform for studying strongly correlated electrons in two dimensions.

Suicide among immigrants in Germany.

AIMS: The identification of high-risk groups is crucial in public health suicide prevention approaches. This study aims to compare suicide risks of Germans with nine of the largest immigrant populations living in Germany. METHODS: Based on a German national database of mortality statistics, the number of suicides in Germans and immigrants was available for the study period (2000 - 2017), stratified for gender and age groups. Standard mortality ratios (SMR) for suicide were computed since age distributions differed between populations. Moreover, SMR of immigrant populations were correlated with potential risk and resilience factors. RESULTS: The analysed dataset covers a period of 18 years, which translates to over 1.47 billion life years (LY) and 206,056 recorded suicides. 134,971,779 LY (10.1%) and 8,936 (4.3%) suicides were assigned to non-German citizens. SMR, calculated for nine of the largest immigrant populations, were lower compared with the German reference population ranging from 0.24 (Greek nationality) to 0.86 (Russian nationality). SMR in immigrants was highest in adolescents and declined with age. SMR was associated with country of origin (CO) suicide rates as well as with socio-economic factors of immigrant groups in Germany. With the global financial crisis, suicide risk of immigrants from the most affected countries decreased more strongly compared to immigrants from other CO. CONCLUSIONS: The suicide risk strongly differs between the individual immigrant groups and is associated with risk factors of the respective CO. Therefore, future suicide prevention approaches in immigrants should take CO-specific vulnerabilities into account as well as age-related risk factors.

Efficacy of Parent-Infant-Psychotherapy with mothers with postpartum mental disorder: study protocol of the randomized controlled trial as part of the SKKIPPI project.

BACKGROUND: After the birth of a child, many mothers and fathers experience postpartum mental disorders like depression, anxiety, obsessive-compulsive disorder, stress or other illnesses. This endangers the establishment of a secure attachment between the children and their primary caregivers. Early problems in parent-child interaction can have adverse long-term effects on the family and the child's well-being. In order to prevent a transgenerational transmission of mental disorders, it is necessary to evaluate psychotherapeutic interventions that target psychologically burdened parents of infants or toddlers. The aim of this trial is to investigate the efficacy of Parent-Infant-Psychotherapy (PIP) for mothers with postpartum mental disorder and their infants (0-12 months). METHODS/DESIGN: In this open, randomized controlled intervention trial 180 mother-infant-dyads will be included and randomly allocated to 12 sessions of PIP or care as usual. The interventions take place either in inpatient adult psychiatric departments or in outpatient settings with home visits. The primary outcome is the change in maternal sensitivity assessed by the Sensitivity subscale of the Emotional Availability Scale (EAS) through videotaped dyadic play-interactions after 6 weeks. Secondary outcomes are maternal psychopathology, stress, parental reflective functioning, infant development and attachment after 6 weeks and 12 months. In addition, maternal attachment (AAI) and reflective functioning (AAI) will be analyzed as potential moderators, and resource usage in the German health system as well as associated costs will be evaluated. DISCUSSION: There is increasing demand for well-controlled studies on psychotherapeutic interventions in the postpartum period that do not only focus on particular risk groups. This randomized controlled trial (RCT) represents one of the first studies to investigate the efficacy of PIP in inpatient psychiatric departments and outpatient care centers in Germany. The results will fill knowledge gaps on the factors contributing to symptom reduction in postpartum mental disorders and improvements in mother-child relationships and help in developing preventive and therapeutic strategies for the fragmented German health care system. TRIAL REGISTRATION: German Register for Clinical Trials, ID: DRKS00016353.

Acoustoelectric Study of Microwave-Induced Current Domains.

Surface acoustic waves (SAW) have been utilized to investigate the properties of a two-dimensional electron system subjected to a perpendicular magnetic field and monochromatic microwave radiation in the regime where the so-called microwave-induced zero-resistance states form. Contrary to conventional magnetotransport in Hall bar and van der Pauw geometries, the collimated SAW beam probes only the bulk of the electronic system exposed to this wave. Clear signatures appear in the SAW propagation velocity, corroborating that neither contacts nor sample edges are a root source for their emergence. By virtue of the directional nature of this probing method and with the assistance of theoretical modeling, we were able to demonstrate that the SAW response depends on the angle between its propagation vector and the orientation of domains that spontaneously form when zero-resistance is observed in transport. This confirms in unprecedented manner the formation of an inhomogeneous phase under these nonequilibrium conditions.

Inherited anxiety-related parent-infant dyads alter LHPA activity.

The pathogenesis of post-traumatic stress disorder (PTSD) is incompletely understood. We hypothesize that disruptions in mother-child relations may be a key contributor to development of PTSD. A normal and healthy separation-individuation process requires adaptations of self- and interactive contingency in both the mother and her child, especially in early childhood development. Anxious mothers are prone to overprotection, which may hinder the individuation process in their children. We examined long-term stress hormones and other stress markers in subjects three generations removed from the Holocaust, to assess the long-term consequences of inherited behavioral and physiological responses to prior stress and trauma. Jewish subjects who recalled overprotective parental behavior had higher hairsteroid-concentrations and dampened limbic-hypothalamic-pituitary-adrenal (LHPA) axis reactivity compared to German and Russian-German subjects with overprotective parents. We suggest that altered LHPA axis activity in maternally overprotected Jewish subjects may indicate a transmitted pathomechanism of "frustrated individuation" resulting from cross-generational anti-Semitic experiences. Thus measurements of hairsteroid-concentrations and parenting practices may have clinical value for diagnosis of PTSD. We propose that this apparent inherited adaptivity of LHPA axis activity could promote higher individual stress resistance, albeit with risk of an allostatic overload.

Current Flow in the Bubble and Stripe Phases.

The spontaneous ordering of spins and charges in geometric patterns is currently under scrutiny in a number of different material systems. A topic of particular interest is the interaction of such ordered phases with itinerant electrons driven by an externally imposed current. It not only provides important information on the charge ordering itself but potentially also allows manipulating the shape and symmetry of the underlying pattern if current flow is strong enough. Unfortunately, conventional transport methods probing the macroscopic resistance suffer from the fact that the voltage drop along the sample edges provides only indirect information on the bulk properties because a complex current distribution is elicited by the inhomogeneous ground state. Here, we promote the use of surface acoustic waves to study these broken-symmetry phases and specifically address the bubble and stripe phases emerging in high-quality two-dimensional electron systems in GaAs/AlGaAs heterostructures as prototypical examples. When driving a unidirectional current, we find a surprising discrepancy between the sound propagation probing the bulk of the sample and the voltage drop along the sample edges. Our results prove that the current-induced modifications observed in resistive transport measurements are in fact a local phenomenon only, leaving the majority of the sample unaltered. More generally, our findings shed new light on the extent to which these ordered electron phases are impacted by an external current and underline the intrinsic advantages of acoustic measurements for the study of such inhomogeneous phases.

Microwave-Induced Oscillations in Magnetocapacitance: Direct Evidence for Nonequilibrium Occupation of Electronic States.

In a two-dimensional electron system, microwave radiation may induce giant resistance oscillations. Their origin has been debated controversially and numerous mechanisms based on very different physical phenomena have been invoked. However, none of them have been unambiguously experimentally identified, since they produce similar effects in transport studies. The capacitance of a two-subband system is sensitive to a redistribution of electrons over energy states, since it entails a shift of the electron charge perpendicular to the plane. In such a system, microwave-induced magnetocapacitance oscillations have been observed. They can only be accounted for by an electron distribution function oscillating with energy due to Landau quantization, one of the quantum mechanisms proposed for the resistance oscillations.

Random flips of electric field in microwave-induced states with spontaneously broken symmetry.

In a two-dimensional electron system subject to microwaves and a magnetic field, photovoltages emerge. They can be separated into two components originating from built-in electric fields and electric field domains arising from spontaneous symmetry breaking. The latter occurs in the zero resistance regime only and manifests itself in pulsed behavior, synchronous across the sample. The pulses show sign reversal. This implies a flip of the field in each domain, consistent with the existence of two equally probable electric field domain configurations due to the spontaneous symmetry breaking.

[Coping and depression in underage children of cancer patients: Data on the course]. / Coping und depressive Belastungen minderjähriger Kinder von Krebspatienten : Verlaufsdaten.

BACKGROUND: There is increasing consideration of a family-focused perspective of the psychosocial consequences of cancer. OBJECTIVES: This study examined the psychosocial situation of children and adolescents (11 to 17 years old) of cancer patients assessing their psychological distress and coping over time. METHODS: A total of 110 children and adolescents were assessed post-treatment of parents with cancer (t1), 6 (t2) and 12 months (t3) after t1. Participants completed validated questionnaires assessing coping (KidCope) and depressive symptoms (CES). These data were compared with a matched sample from the general population. RESULTS: The children reported using a combination of coping measures. In particular, active coping was perceived as being helpful. In terms of coping, there were only small gender differences and 6 months after completion of treatment of the parents (t2), depressive symptoms of the children were still elevated. Depression diminished over time and was near the level of the comparison group at t3. CONCLUSION: Children and adolescents are particularly psychologically distressed after cancer treatment of parents. This distress was connected with not helpful coping strategies. The extended adjustment of children/adolescents of cancer patients has to be considered in the clinical and psychosocial care of the families.

Coupling of Josephson currents in quantum Hall bilayers.

We study ring-shaped (Corbino) devices made of bilayer two-dimensional electron gases in the total filling factor one quantized Hall phase, which is considered to be a coherent Bardeen-Cooper-Schrieffer-like state of interlayer excitons. Identical Josephson currents are observed at the two edges while only a negligible conductance between them is found. The maximum Josephson current observed at either edge can be controlled by passing a second interlayer Josephson current at the other edge. Because of the large electric resistance between the two edges, the interaction between them can only be mediated by the neutral interlayer excitonic ground state.

Quantized ν = 5/2 state in a two-subband quantum hall system.

The evolution of the fractional quantum Hall state at filling 5/2 is studied in density tunable two-dimensional electron systems formed in wide wells in which it is possible to induce a transition from single- to two-subband occupancy. In 80 and 60 nm wells, the quantum Hall state at 5/2 filling of the lowest subband is observed even when the second subband is occupied. In a 50 nm well, the 5/2 state vanishes upon second subband population. We attribute this distinct behavior to the width dependence of the capacitive energy for intersubband charge transfer and of the overlap of the subband probability densities.

Metrology and microscopic picture of the integer quantum Hall effect.

Since 1990, the integer quantum Hall effect has provided the electrical resistance standard, and there has been a firm belief that the measured quantum Hall resistances are described only by fundamental physical constants--the elementary charge e and the Planck constant h. The metrological application seems not to rely on detailed knowledge of the microscopic picture of the quantum Hall effect; however, technical guidelines are recommended to confirm the quality of the sample to confirm the exactness of the measured resistance value. In this paper, we give our present understanding of the microscopic picture, derived from systematic scanning force microscopy investigations on GaAs/(AlGa)As quantum Hall samples, and relate these to the technical guidelines.

Collective modes and the periodicity of quantum Hall stripes.

We investigate the quantum Hall stripe phase at filling factor 9/2 at the microscopic level by probing the dispersion of its collective modes with the help of surface acoustic waves with wavelengths down to 60 nm. The dispersion is strongly anisotropic. It is highly dispersive and exhibits a roton minimum for wave vectors aligned along the easy transport direction. In the perpendicular direction, however, the dispersion is featureless, although not flat as predicted by theory. Oscillatory behavior in the absorption intensity of the collective mode with a wave vector perpendicular to the stripes is attributed to a commensurability effect. It allows us to extract the periodicity of the quantum Hall stripes.

[Child health as a prevention objective in the context of the pilot project "Pro Kind". Preliminary results of a randomized controlled trial]. / Präventionsziel Kindergesundheit im Rahmen des Modellprojektes "Pro Kind". Vorläufige Befunde einer längsschnittlichen, randomisierten Kontrollgruppenstudie.

A randomized controlled trial (RCT) was conducted to assess the effectiveness of the home visiting program "Pro Kind". A total of 755 primiparae with multiple risk factors were recruited through the end of 2009 in three German federal states (Lower Saxony, Bremen, Saxony) and were randomized into one of two research groups. All participants had access to standard community service; women in the treatment group also received a program of home visitation over a period of 2.5 years. Primary objectives were improvement of maternal health behavior during pregnancy and birth of a healthy child. Long-term objectives are better outcomes of child health and development. To date, significant group differences in the primary objective variables are not detectable. Interim analyses at the ages of 6 and 12 months showed a tendency for a positive treatment effect on cognitive development. Methodological and practical limitations are critically discussed.

Interlayer tunneling in counterflow experiments on the excitonic condensate in quantum Hall bilayers.

The effect of tunneling on the transport properties of quantum Hall double layers in the regime of the excitonic condensate at a total filling factor one is studied in counterflow experiments. If the tunnel current I is smaller than a critical I{C}, tunneling is large and is effectively shorting the two layers. For I>I{C} tunneling becomes negligible. Surprisingly, the transition between the two tunneling regimes has only a minor impact on the features of the filling-factor one state as observed in magnetotransport, but at currents exceeding I{C} the resistance along the layers increases rapidly.

Photocurrent and photovoltage oscillations in the two-dimensional electron system: enhancement and suppression of built-in electric fields.

We observe microwave-induced photocurrent and photovoltage oscillations around zero as a function of the applied magnetic field in high mobility GaAs 2D electron systems. The photosignals pass zero whenever the microwave frequency is close to a multiple of the cyclotron resonance frequency. They originate from built-in electric fields due to for instance band bending at contacts. The oscillations correspond to a suppression (screening) or an enhancement ("antiscreening") of these fields by the photoexcited electrons.

Nature of the spin transition in the half-filled Landau level.

We report transport and nuclear spin relaxation studies of a density tunable two-dimensional electron system at filling nu=1/2 in tilted magnetic fields. The transition from partial to full spin polarization with an in-plane field leaves a clear signature in the resistance. Nuclear spin relaxation studies suggest that puddles of minority spins are responsible for an observed non-Korringa temperature dependence. This inhomogeneous spin polarization, similarly encountered in manganites where it strongly affects resistance, may help with understanding the spin dependent transport at nu=1/2.

Tunable plasmonic crystals for edge magnetoplasmons of a two-dimensional electron system.

Plasmonic crystal effects analogous to photonic crystal phenomena such as zone folding and gap opening were observed for edge magnetoplasmons in a two-dimensional electron system with a periodically corrugated boundary at microwave frequencies. Magnetic field dependent photovoltage data provide unequivocal evidence for Bragg reflection. Band gaps up to fifth order were observed. These gaps were investigated as a function of the electron density, the magnetic field, and the periodicity to demonstrate the tunability of the dispersive properties of these plasmonic crystals.

Dispersion of the composite-fermion cyclotron-resonance mode.

The dispersion of the composite-fermion cyclotron-resonance mode is measured with an optical detection scheme under the combined excitation of microwave radiation and a surface acoustic wave from an interdigital transducer. The slowly traveling surface wave defines the transferred wave vector. Momenta up to 10;{8} m;{-1} are accessible. The cyclotron-resonance mode exhibits strong negative dispersion, which suggests predominant short range residual interaction among composite fermions. From an extrapolation, the cyclotron mass at k=0 is obtained and investigated as a function of electron density.