Direct probing of band-structure Berry phase in diluted magnetic semiconductors

We report on experimental evidence of the Berry phase accumulated by the charge carrier wave function in single-domain nanowires made from a (Ga,Mn)(As,P) diluted ferromagnetic semiconductor layer. Its signature on the mesoscopic transport measurements is revealed as unusual patterns in the magnetoconductance, that are clearly distinguished from the universal conductance fluctuations. We show that these patterns appear in a magnetic field region where the magnetization rotates coherently and are related to a change in the band-structure Berry phase as the magnetization direction changes. They should be thus considered as a band structure Berry phase fingerprint of the effective magnetic monopoles in the momentum space. We argue that this is an efficient method to vary the band structure in a controlled way and to probe it directly. Hence, (Ga,Mn)As appears to be a very interesting test bench for new concepts based on this geometrical phase.Comment: 7 pages, 6 figure

Ridesourcing and Travel Demand: Potential Effects of Transportation Network Companies in Bogotá

This paper proposes a modal-shift analysis methodology based on a mix of small-scale primary data and big data sources to estimate the total amount of trips that are reallocated to transportation network companies (TNCs) services in Bogotá, Colombia. The analysis is focused on the following four modes: public transportation, private vehicles, conventional taxis, and TNC services. Based on a stated preferences survey and secondary databases of travel times and costs, the paper proposes a methodology to estimate the reallocation of travel demand once TNCs start operating. Results suggests that approximately one third of public transportation trips are potentially transferred to TNCs. Moreover, potential taxi and private vehicle–transferred trips account for almost 30% of the new TNC demand. Additionally, approximately half of the trips that are reallocated from public transport demand can be considered as complementary, while the remaining share can be considered as potential replacing trips of public transportation. The paper also estimates the potential increase in Vehicle-km travelled in each of the modes before and after substitution as a proxy to the effects of demand reallocation on sustainability, finding increases between 1.3 and 14.5 times the number of Vehicle-km depending on the mode. The paper highlights the role of open data and critical perspectives on available information to analyze potential scenarios of the introduction of disruptive technologies and their spatial, social, and economic implications

Informe sobre la esperanza. Diálogo con el cardenal Gerhard Ludwig Müller [Reseña]

Reseña a G.L. Müller, Informe sobre la esperanza. Diálogo con el cardenal Gerhard Ludwig Müller, Madrid: BAC, 2016, 238 pp., 12.5x20,5, ISBN 978-84-220-1889-6

Transmitir hoy la fe en Cristo. XXIV Encuentro de Obispos y Teólogos. Reunión de la Comisión teológica asesora [Reseña]

Reseña a A. del Agua (ed.) Transmitir hoy la fe en Cristo, XXIV Encuentro de Obispos y Teólogos. Reunión de la Comisión teológica asesora, Madrid: Edice, 2015, 340 pp., 13,5x21, ISBN 978-84-7141-831-

Formalism for obtaining nuclear momentum distributions by the Deep Inelastic Neutron Scattering technique

We present a new formalism to obtain momentum distributions in condensed matter from Neutron Compton Profiles measured by the Deep Inelastic Neutron Scattering technique. The formalism describes exactly the Neutron Compton Profiles as an integral in the momentum variable $y$. As a result we obtain a Volterra equation of the first kind that relates the experimentally measured magnitude with the momentum distributions of the nuclei in the sample. The integration kernel is related with the incident neutron spectrum, the total cross section of the filter analyzer and the detectors efficiency function. A comparison of the present formalism with the customarily employed approximation based on a convolution of the momentum distribution with a resolution function is presented. We describe the inaccuracies that the use of this approximation produces, and propose a new data treatment procedure based on the present formalism.Comment: 11 pages, 8 figure

Measurement of the total cross section of heavy water in the 0.1 meV–1 eV energy range at 20 and 50 ◦C

Despite the importance of heavy water as a neutron moderator, there are few measurements of its total neutron cross section for cold and thermal energies, and none of them covers the range of temperature (40–70◦C) used in moderator and reflector tanks in research reactors, and in CANDU nuclear power plants. To cover this deficit, we measured the total cross section of liquid heavy water at 20◦C and 50◦C using the SANS beamline at the LENS facility at Indiana University. The time-of-flight technique was used, in a sample-in/sample-out measurement. The use of the solid methane cold neutron source at LENS allowed measuring in a broad range in energy, from 0.1meV to 1 eV. In this paper we present details of the measurement and processing of the data, and comparison with previous experimental measurements and calculation models. This work is included in the Action Plan of the IAEA Coordinated Research Project “Advanced Moderators for Intense Cold Neutron Beams in Materials Research”

Anisotropic Magnetoresistance in Manganites: Model and Experiment

We present measurements of anisotropic magnetoresistance of La_{0.75}Sr_{0.25}MnO_3 films deposited on (001) SrTiO_3 substrates, and develop a model to describe the low temperature AMR in manganites. We measure an AMR of the order of 10^{-3} for the current I parallel to the [100] axis of the crystal and vanishing AMR for I//[110], in agreement with the model predictions.Comment: 4 pages, 4 figure

Sensing domain wall pinning in the longitudinal magnetoresistance of a two-dimensional electron gas

We investigate the sensing of domain wall pinning in thin Co wires positioned on top of a two-dimensional electron gas (2DEG) heterostructure by measuring the longitudinal resistance of the 2DEG as the magnetic field is swept, in an analogy to the Barkhausen effect. For comparison, we also measure the magnetoresistance of the ferromagnetic film in the same device in a subsequent sweep. Compared to the Hall measurements, the longitudinal measurement has the advantage of sensing magnetic activity over longer lengths, while compared to the measurement of the magnetoresistance in the ferromagnetic wire, it offers complementary information related to the pinning and unpinning of the domain wall, due to its sensitivity only to the out-of-plane magnetic field component.Fil: Kazazis, D.. No especifíca;Fil: Schüler, B.. Heinrich Heine University; AlemaniaFil: Granada, Mara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Gennser, U.. No especifíca;Fil: Faini, G.. No especifíca;Fil: Cerchez, M.. Heinrich Heine University; AlemaniaFil: Heinzel, T.. Heinrich Heine University; Alemani