Sustainability assessment of organic dairy farms in mountainous areas of Austria

Dairy farming plays a major role in mountainous regions of Austria, mostly due to high proportion of grasslands. In general, Austria’s dairy farming faces challenges regarding sustainability, e.g. environmental impacts, but specifically for alpine areas low productivity and dependency on direct payments are lowering sustainability. Organic farming is considered as a strategy to overcome these challenges. Considering this general background, we analysed the sustainability performance and its main drivers of organic dairy farms in mountainous regions of Austria

Functionalization of transparent conductive oxide electrode for TiO2-free perovskite solar cells

Many of the best performing solar cells based on perovskite-halide light absorbers use TiO2 as an electron selective contact layer. However, TiO2 usually requires high temperature sintering, is related to electrical instabilities in perovskite solar cells, and causes cell performance degradation under full solar spectrum illumination. Here we demonstrate an alternative approach based on the modification of transparent conductive oxide electrodes with self-assembled siloxane-functionalized fullerene molecules, eliminating TiO2 or any other additional electron transporting layer. We demonstrate that these molecules spontaneously form a homogenous monolayer acting as an electron selective layer on top of the fluorine doped tin oxide (FTO) electrode, minimizing material consumption. We find that the fullerene-modified FTO is a robust, chemically inert charge selective contact for perovskite based solar cells, which can reach 15% of stabilised power conversion efficiency in a flat junction device architecture using a scalable, low temperature, and reliable process. In contrast to TiO2, devices employing a molecularly thin functionalized fullerene layer show unaffected performance after 67 h of UV light exposure

Diamagnetism of real-space pairs above Tc in hole doped cuprates

The nonlinear normal state diamagnetism reported by Lu Li et al. [Phys. Rev. B 81, 054510 (2010)] is shown to be incompatible with an acclaimed Cooper pairing and vortex liquid above the resistive critical temperature. Instead it is perfectly compatible with the normal state Landau diamagnetism of real-space composed bosons, which describes the nonlinear magnetization curves in less anisotropic cuprates La-Sr-Cu-O (LSCO) and Y-Ba-Cu-O (YBCO) as well as in strongly anisotropic bismuth-based cuprates in the whole range of available magnetic fields.Comment: 4 pages, 4 figure

Electron-Phonon Coupling in High-Temperature Cuprate Superconductors Determined from Electron Relaxation Rates

We determined electronic relaxation times via pump-probe optical spectroscopy using sub-15 fs pulses for the normal state of two different cuprate superconductors.We show that the primary relaxation process is the electron-phonon interaction and extract a measure of its strength, the second moment of the Eliashberg function\lambda=800\pm200 meV^{2} for La_{1.85}Sr_{0.15}CuO_{4} and \lambda=400\pm100 meV^{2} for YBa_{2}Cu_{3}O_{6.5}. These values suggest a possible fundamental role of the electron-phonon interaction in the superconducting pairing mechanism.Comment: As published in PR

Disentangling the electronic and phononic glue in a high-Tc superconductor

Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamen- tal step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (\Omega) dependent bosonic function, \Pi(\Omega). We perform optical spectroscopy on Bi2212 crystals with simultaneous time- and frequency-resolution; this technique allows us to disentangle the electronic and phononic contributions by their different temporal evolution. The strength of the interaction ({\lambda}~1.1) with the electronic excitations and their spectral distribution fully account for the high critical temperature of the superconducting phase transition.Comment: 9 pages, 4 figure

Theory of excited state absorptions in phenylene-based π\pi-conjugated polymers

Within a rigid-band correlated electron model for oligomers of poly-(paraphenylene) (PPP) and poly-(paraphenylenevinylene) (PPV), we show that there exist two fundamentally different classes of two-photon A$_g$ states in these systems to which photoinduced absorption (PA) can occur. At relatively lower energies there occur A$_g$ states which are superpositions of one electron - one hole (1e--1h) and two electron -- two hole (2e--2h) excitations, that are both comprised of the highest delocalized valence band and the lowest delocalized conduction band states only. The dominant PA is to one specific member of this class of states (the mA$_g$). In addition to the above class of A$_g$ states, PA can also occur to a higher energy kA$_g$ state whose 2e--2h component is {\em different} and has significant contributions from excitations involving both delocalized and localized bands. Our calculated scaled energies of the mA$_g$ and the kA$_g$ agree reasonably well to the experimentally observed low and high energy PAs in PPV. The calculated relative intensities of the two PAs are also in qualitative agreement with experiment. In the case of ladder-type PPP and its oligomers, we predict from our theoretical work a new intense PA at an energy considerably lower than the region where PA have been observed currently. Based on earlier work that showed that efficient charge--carrier generation occurs upon excitation to odd--parity states that involve both delocalized and localized bands, we speculate that it is the characteristic electronic nature of the kA$_g$ that leads to charge generation subsequent to excitation to this state, as found experimentally.Comment: Revtex4 style, 2 figures inserted in the text, three tables, 10 page

Strain-induced enhancement of the electron energy relaxation in strongly correlated superconductors

We use femtosecond optical spectroscopy to systematically measure the primary energy relaxation rate k1 of photoexcited carriers in cuprate and pnictide superconductors. We find that k1 increases monotonically with increased negative strain in the crystallographic a-axis. Generally, the Bardeen-Shockley deformation potential theorem and, specifically, pressure-induced Raman shifts reported in the literature suggest that increased negative strain enhances electron-phonon coupling, which implies that the observed direct correspondence between a and k1 is consistent with the canonical assignment of k1 to the electron-phonon interaction. The well-known non-monotonic dependence of the superconducting critical temperature Tc on the a-axis strain is also reflected in a systematic dependence Tc on k1, with a distinct maximum at intermediate values (~16 ps-1 at room temperature). The empirical non-monotonic systematic variation of Tc with the strength of the electron-phonon interaction provides us with unique insight into the role of electron-phonon interaction in relation to the mechanism of high-Tc superconductivity as a crossover phenomenon.Comment: manuscript as accepted in PRX, main paper (20 pages, 3 figures) plus supplementary material (25 pages, 19 figures

Exciton bimolecular annihilation dynamics in supramolecular nanostructures of conjugated oligomers

We present femtosecond transient absorption measurements on $\pi$-conjugated supramolecular assemblies in a high pump fluence regime. Oligo(\emph{p}-phenylenevinylene) monofunctionalized with ureido-\emph{s}-triazine (MOPV) self-assembles into chiral stacks in dodecane solution below 75$^{\circ}$C at a concentration of $4\times 10^{-4}$ M. We observe exciton bimolecular annihilation in MOPV stacks at high excitation fluence, indicated by the fluence-dependent decay of $1^1$B$_{u}$-exciton spectral signatures, and by the sub-linear fluence dependence of time- and wavelength-integrated photoluminescence (PL) intensity. These two characteristics are much less pronounced in MOPV solution where the phase equilibrium is shifted significantly away from supramolecular assembly, slightly below the transition temperature. A mesoscopic rate-equation model is applied to extract the bimolecular annihilation rate constant from the excitation fluence dependence of transient absorption and PL signals. The results demonstrate that the bimolecular annihilation rate is very high with a square-root dependence in time. The exciton annihilation results from a combination of fast exciton diffusion and resonance energy transfer. The supramolecular nanostructures studied here have electronic properties that are intermediate between molecular aggregates and polymeric semiconductors

Effect of screening of the electron-phonon interaction on the temperature of Bose-Einstein condensation of intersite bipolarons

Here we consider an interacting electron-phonon system within the framework of extended Holstein-Hubbard model at strong enough electron-phonon interaction limit in which (bi)polarons are the essential quasiparticles of the system. It is assumed that the electron-phonon interaction is screened and its potential has Yukawa-type analytical form. An effect of screening of the electron-phonon interaction on the temperature of Bose-Einstein condensation of the intersite bipolarons is studied for the first time. It is revealed that the temperature of Bose-Einstein condensation of intersite bipolarons is higher in the system with the more screened electron-phonon interaction.Comment: 6 pages, 4 figure