Strain-gradient mediated local conduction in strained bismuth ferrite films

It has been recently shown that the strain gradient is able to separate the light-excited electron-hole pairs in semiconductors, but how it affects the photoelectric properties of the photo-active materials remains an open question. Here, we demonstrate the critical role of the strain gradient in mediating local photoelectric properties in the strained BiFeO3 thin films by systematically characterizing the local conduction with nanometre lateral resolution in both dark and illuminated conditions. Due to the giant strain gradient manifested at the morphotropic phase boundaries, the associated flexo-photovoltaic effect induces on one side an enhanced photoconduction in the R-phase, and on the other side a negative photoconductivity in the morphotropic [Formula: see text]-phase. This work offers insight and implication of the strain gradient on the electronic properties in both optoelectronic and photovoltaic devices

Structural and photoelectric properties of tensile strained BiFeO3

An in-depth structural study of a 23-nm-thick BiFeO3 film grown on orthorhombic NdScO3(110)O substrates demonstrates the presence of a mixed phases. Atomic resolution scanning transmission electron microscopy measurements reveal an out-of-plane stripe domain structure typical of rhombohedral BiFeO3 films but with a polarization component along pseudocubic ⟨100⟩PC or canted from the ⟨111⟩PC towards the in-plane direction. Photovoltaic measurements display an anomalous modulation of the open circuit voltage as temperature is decreased that is attributed to a structural change associated with a transition to a single structural phase

Polarization curling and flux closures in multiferroic tunnel junctions

Formation of domain walls in ferroelectrics is not energetically favourable in low-dimensional systems. Instead, vortex-type structures are formed that are driven by depolarization fields occurring in such systems. Consequently, polarization vortices have only been experimentally found in systems in which these fields are deliberately maximized, that is, in films between insulating layers. As such configurations are devoid of screening charges provided by metal electrodes, commonly used in electronic devices, it is wise to investigate if curling polarization structures are innate to ferroelectricity or induced by the absence of electrodes. Here we show that in unpoled Co/PbTiO3/(La,Sr)MnO3 ferroelectric tunnel junctions, the polarization in active PbTiO3 layers 9 unit cells thick forms Kittel-like domains, while at 6 unit cells there is a complex flux-closure curling behaviour resembling an incommensurate phase. Reducing the thickness to 3 unit cells, there is an almost complete loss of switchable polarization associated with an internal gradient

Bi-ferroic memristive properties of multiferroic tunnel junctions

The giant tunnelling electroresistance (TER) and memristive behaviours of ferroelectric tunnel junctions make them promising candidates for future information storage technology. Using conducting ferromagnetic layers as electrodes results in multiferroic tunnel junctions (MFTJs) which show spin dependent transport. The tunnelling magnetoresistance (TMR) of such structures can be reversibly controlled by electric pulsing owing to ferroelectric polarisation-dependent spin polarisation at the ferroelectric/ferromagnetic interface. Here, we show multilevel electric control of both TMR and TER of MFTJs, which indicates the bi-ferroic or magneto-electric memristive properties. This effect is realised by manipulating the ferroelectric domain configuration via non-volatile partial ferroelectric switching obtained by applying low voltage pulses to the junction. Through electrically modulating the ratio between up- and down-polarised ferroelectric domains, a broad range of TMR (between ∼3% and ∼30%) and TER (∼1000%) values can be achieved. The multilevel control of TMR and TER using the electric pulse tunable ferroelectric domain configuration suggests a viable way to obtain multiple state memory

Full configuration interaction calculation of BeH adiabatic states

An all-electron full configuration interaction (FCI) calculation of the adiabatic potential energy curves of some of the lower states of BeH molecule is presented. A moderately large ANO basis set of atomic natural orbitals (ANO) augmented with Rydberg functions has been used in order to describe the valence and Rydberg states and their interactions. The Rydberg set of ANOs has been placed on the Be at all bond distances. So, the basis set can be described as 4s3p2d1f/3s2p1d(Be/H)+4s4p2d(Be). The dipole moments of several states and transition dipole strengths from the ground state are also reported as a function of the RBe–H distance. The position and the number of states involved in several avoided crossings present in this system have been discussed. Spectroscopic parameters have been calculated from a number of the vibrational states that result from the adiabatic curves except for some states in which this would be completely nonsense, as it is the case for the very distorted curves of the 3s and 3p math states or the double-well potential of the 4p math state. The so-called “D complex” at 54 050 cm−1 (185.0 nm) is resolved into the three 3d substates (math,math,math). A diexcited valence state is calculated as the lowest state of math symmetry and its spectroscopic parameters are reported, as well as those of the 2 math (4d) state The adiabatic curve of the 4 math state shows a swallow well at large distances (around 4.1 Å) as a result of an avoided crossing with the 3 math state. The probability that some vibrational levels of this well could be populated is discussed within an approached Landau–Zerner model and is found to be high. No evidence is found of the E(4sσ) math state in the region of the “D complex”. Instead, the spectroscopic properties obtained from the (4sσ) 6 math adiabatic curve of the present work seem to agree with those of the experimental F(4pσ) math state. The FCI calculations provide benchmark results for other correlation models for the open-shell BeH system and evidence both the limitations and capabilities of the basis [email protected] [email protected]

Breathers in a system with helicity and dipole interaction

Recent papers that have studied variants of the Peyrard-Bishop model for DNA, have taken into account the long range interaction due to the dipole moments of the hydrogen bonds between base pairs. In these models the helicity of the double strand is not considered. In this particular paper we have performed an analysis of the influence of the helicity on the properties of static and moving breathers in a Klein--Gordon chain with dipole-dipole interaction. It has been found that the helicity enlarges the range of existence and stability of static breathers, although this effect is small for a typical helical structure of DNA. However the effect of the orientation of the dipole moments is considerably higher with transcendental consequences for the existence of mobile breathers.Comment: 4pages, 5 eps figure

An epidemiological survey on the leishmaniosis in the Campo de Nijar' s area (Almeria)

Se ha realizado un estudio epidemiológico sobre la leishmaniosis en el área Sur del matiz climático Mediterráneo Subdesértico de la provincia de Almería (Campo de Níjar, Sudeste de España). A una muestra de la población humana se le aplicó la Intradermorreacción de Montenegro (IDR): de 1.370 inoculados, sólo 33 (2'4 %) fueron positivos (induración >= 5 mm). De la población canina, se analizaron mediante Inmunofluorescencia Indirecta (IFI) 286 muestras de suero, de las que 174 (60'8 %) fueron negativas, y las 112 restantes tuvieron algún título (39'2 % de seropositividad); de éstas últimas sólo 13 presentaron titulo >= 160 (seroprevalencia del 4'5 %). El estudio se completó con la captura de vectores: 1) con trampas adhesivas se capturaron 216 ejemplares pertenecientes a las especies Sergentomyia minuta (62 %), Phlebotomus perniciosus (34'3 %), Y P. ariasi y P. papatasí (3'7 %). 2) Trampas CDC: se capturaron 790 ejemplares pertenecientes a las especies P. perniciosus (73 %), P. papatasi (22'2 %), Y P. ariasi, P. longicuspis, P. alexandri, P. sergenti y S. minuta (4'8 %). Aunque se diseccionaron 530 ejemplares hembras ninguna estuvo parasitada por Leíshmania.We have realised an epidemiological study on the Leishmaniosis in the Southem area from Subdesertic Mediterranean bioclimatic zone, of the Almeria' s province (Campo de Níjar, Southeast Spain). The Montenegro Skin test (IDR) was applied to a sample of human population: of 1.370 individuals inoculated, only 33 (2'4 %) were positives (induration >= 5 mm). The canine population was analysed by Immunofluorescent Antibody test (IFI): of 286 sample of serum analysed, 174 were negatives (60'9%) and 112 were with antibody titles >= 20 (39'2 % seropositivites); of these only 13 were with title >= 160 (seroprevalence of 4'5 %).   The study was completed with the capture of vectors: 1) with sticky traps we capture 216 specimens belonging to the species S. minuta (62 %), P. perniciosus, (34'3 %), and P. ariasi and P. papatasi (3 '7 %). 2) With CDC traps we capture 790 specimens to the species P. perniciosus (73 %), P. papatas; (22'2), P. ariasi, P. longicuspis, P. sergenti, P. alexandri and S. minuta (4' 8 %). Although we have diseccionate 530 specimens female none of them was parasitized by Leishmania

Minimax Current Density Coil Design

'Coil design' is an inverse problem in which arrangements of wire are designed to generate a prescribed magnetic field when energized with electric current. The design of gradient and shim coils for magnetic resonance imaging (MRI) are important examples of coil design. The magnetic fields that these coils generate are usually required to be both strong and accurate. Other electromagnetic properties of the coils, such as inductance, may be considered in the design process, which becomes an optimization problem. The maximum current density is additionally optimized in this work and the resultant coils are investigated for performance and practicality. Coils with minimax current density were found to exhibit maximally spread wires and may help disperse localized regions of Joule heating. They also produce the highest possible magnetic field strength per unit current for any given surface and wire size. Three different flavours of boundary element method that employ different basis functions (triangular elements with uniform current, cylindrical elements with sinusoidal current and conic section elements with sinusoidal-uniform current) were used with this approach to illustrate its generality.Comment: 24 pages, 6 figures, 2 tables. To appear in Journal of Physics D: Applied Physic