Inhomogeneous ferrimagnetic-like behavior in Gd2/3Ca1/3MnO3 single crystals

We present a study of the magnetic properties of Gd2/3Ca1/3MnO3 single crystals at low temperatures. We show that this material behave as an inhomogeneous ferrimagnet. In addition to small saturation magnetization at 5 K, we have found history dependent effects in the magnetization and the presence of exchange bias. These features are compatible with microscopic phase separation in the clean Gd2/3Ca1/3MnO3 system studied.Comment: 7 pages, 6 figures, submitted Journal of Magnetism and Magnetic Material

Microstructural control of the transport properties of β-FeSe films grown by sputtering

We have investigated the correlation between structural and transport properties in sputtered β-FeSe films grown onto SrTiO3 (100). The growth parameters, such as substrate temperature and thickness, have been varied in order to explore different regimes. In the limit of textured thick films, we found promising features like an enhanced Tc ∼ 12K, a relatively high Hc2 and a low anisotropy. By performing magnetoresistance and Hall coefficient measurements, we investigate the influence of the disorder associated with the textured morphology on some features attributed to subtle details of the multi-band electronic structure of β-FeSe. Regarding the superconductor-insulator transition (SIT) induced by reducing the thickness, we found a non-trivial evolution of the structural properties and morphology associated with a strained initial growth and the coalescence of grains. Our results reveal the key effects on the macroscopic electronic behaviour played by the lattice distortion in thin insulating samples and by the grain morphology in thicker superconducting films.Fil: Ale Crivillero, María Victoria. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Amigo, M.. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Haberkorn, Nestor Fabian. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Nieva, G.. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); ArgentinaFil: Guimpel, Julio Juan. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentin

Influence of ion implantation on the magnetic and transport properties of manganite films

We have used oxygen ions irradiation to generate controlled structural disorder in thin manganite films. Conductive atomic force microscopy CAFM), transport and magnetic measurements were performed to analyze the influence of the implantation process in the physical properties of the films. CAFM images show regions with different conductivity values, probably due to the random distribution of point defect or inhomogeneous changes of the local Mn3+/4+ ratio to reduce lattice strains of the irradiated areas. The transport and magnetic properties of these systems are interpreted in this context. Metal-insulator transition can be described in the frame of a percolative model. Disorder increases the distance between conducting regions, lowering the observed TMI. Point defect disorder increases localization of the carriers due to increased disorder and locally enhanced strain field. Remarkably, even with the inhomogeneous nature of the samples, no sign of low field magnetoresistance was found. Point defect disorder decreases the system magnetization but doesn t seem to change the magnetic transition temperature. As a consequence, an important decoupling between the magnetic and the metal-insulator transition is found for ion irradiated films as opposed to the classical double exchange model scenario.Comment: 27 pages, 11 Figure

Low-temperature thermal expansion of the topological material candidates β\beta-PtBi2_2 and β\beta-Bi2_2Pd

We report on the low-temperature ($T <$ 120 K) thermal expansion of the bismuth-based topological semimetal $\beta$-PtBi$_2$ and topological superconductor $\beta$-Bi$_2$Pd candidates. The linear thermal-expansion coefficient of tetragonal $\beta$-Bi$_2$Pd shows a pronounced anisotropy between the $a$- and $c$-axis while the volume thermal-expansion coefficient $\alpha_V$($\beta$-Bi$_2$Pd) is considerable larger than $\alpha_V$($\beta$-PtBi$_2$). The coefficient $\alpha_V$($\beta$-PtBi$_2$) nearly matches the experimental specific heat, from which a Debye temperature $\theta_D =$ 199 K is obtained. On the other hand, $\alpha_V$($\beta$-Bi$_2$Pd) reasonably fits the Debye model with $\theta_D =$ 138 K, extracted from the low-temperature specific heat. An almost constant Gr\"uneisen parameter $\Gamma \approx$ 2 is obtained for both compounds. No magnetostriction is observed in any of both compounds up to $\mu_0 H =$ 16 T. We compare our results with other Bi-based topological materials.Comment: 7 pages, 3 figure

Impurity band in clean superconducting weak links

Weak impurity scattering produces a narrow band with a finite density of states near the phase difference $\phi =\pi$ in the mid-gap energy spectrum of a macroscopic superconducting weak link. The equivalent distribution of transmission coefficients of various cunducting quantum channels is found.Comment: 4 pages, 4 figures, changed conten

Comparison between 68Ga-bombesin (68Ga-BZH3) and the cRGD tetramer 68Ga-RGD4 studies in an experimental nude rat model with a neuroendocrine pancreatic tumor cell line

BACKGROUND: Serotonergic neurons in the rodent hypothalamus are implicated in key neuroendocrine and metabolic functions, including circadian rhythmicity. However, the assessment of the serotonergic system in the human hypothalamus in vivo is difficult as delineation of the hypothalamus is cumbersome with conventional region-of-interest analysis. In the present study, we aimed to develop a method to visualize serotonin transporters (SERT) in the hypothalamus. Additionally, we tested the hypothesis that hypothalamic SERT binding ratios are different between patients with hypothalamic impairment (HI), pituitary insufficiency (PI), and control subjects (C). METHODS: SERT availability was determined in 17 subjects (6 HI, 5 PI, and 6 healthy controls), 2 h after injection of 123I-N-ω-fluoropropyl-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane ([123I]FP-CIT), using single-photon emission computed tomography (performed on a brain-dedicated system) fused with individual magnetic resonance imaging (MRI) scans of the brain. The hypothalamus (representing specific SERT binding) and cerebellum (representing nonspecific binding) were manually delineated on each MRI to assess [123I]FP-CIT binding and specific-to-nonspecific binding ratios. RESULTS: In each healthy subject, [123I]FP-CIT binding was higher in the hypothalamus than in the cerebellum, and the mean hypothalamic binding ratio of SERT was 0.29 ± 0.23. We found no difference in hypothalamic binding ratios between HI, PI, and control subjects (HI 0.16 ± 0.24, PI 0.45 ± 0.39, C 0.29 ± 0.23, p value 0.281). CONCLUSIONS: We were able to demonstrate SERT binding in the human hypothalamus in vivo. However, we did not find altered hypothalamic SERT binding in patients with hypothalamic impairment. TRIAL REGISTRATION: Netherlands Trial Register: NTR2520

Giant Josephson current through a single bound state in a superconducting tunnel junction

We study the microscopic structure of the Josephson current in a single-mode tunnel junction with a wide quasiclassical tunnel barrier. In such a junction each Andreev bound state carries a current of magnitude proportional to the {\em amplitude} of the normal electron transmission through the junction. Tremendous enhancement of the bound state current is caused by the resonance coupling of superconducting bound states at both superconductor-insulator interfaces of the junction. The possibility of experimental observation of the single bound state current is discussed.Comment: 11 pages, [aps,preprint]{revtex