Nodal-to-nodeless superconducting order parameter in LaFeAs1−x_{1-x}Px_xO synthesized under high pressure

Similar to chemical doping, pressure produces and stabilizes new phases of known materials, whose properties may differ greatly from those of their standard counterparts. Here, by considering a series of LaFeAs$_{1-x}$P$_x$O iron-pnictides synthesized under high-pressure high-temperature conditions, we investigate the simultaneous effects of pressure and isoelectronic doping in the 1111 family. Results of numerous macro- and microscopic technique measurements, unambiguously show a radically different phase diagram for the pressure-grown materials, characterized by the lack of magnetic order and the persistence of superconductivity across the whole $0.3 \leq x \leq 0.7$ doping range. This unexpected scenario is accompanied by a branching in the electronic properties across $x = 0.5$, involving both the normal and superconducting phases. Most notably, the superconducting order parameter evolves from nodal (for $x < 0.5$) to nodeless (for $x \geq 0.5$), in clear contrast to other 1111 and 122 iron-based materials grown under ambient-pressure conditions.Comment: 9 pages, 7 figures, Suppl. materia

Probing Quantized Einstein-Rosen Waves with Massless Scalar Matter

The purpose of this paper is to discuss in detail the use of scalar matter coupled to linearly polarized Einstein-Rosen waves as a probe to study quantum gravity in the restricted setting provided by this symmetry reduction of general relativity. We will obtain the relevant Hamiltonian and quantize it with the techniques already used for the purely gravitational case. Finally we will discuss the use of particle-like modes of the quantized fields to operationally explore some of the features of quantum gravity within this framework. Specifically we will study two-point functions, the Newton-Wigner propagator, and radial wave functions for one-particle states.Comment: Accepted for publication in Physical Review

Alignment transition in a nematic liquid crystal due to field-induced breaking of anchoring

We report on the alignment transition of a nematic liquid crystal from initially homeotropic to quasi-planar due to field-induced anchoring breaking. The initial homeotropic alignment is achieved by Langmuir-Blodgett monolayers. In this geometry the anchoring strength can be evaluated by the Frederiks transition technique. Applying an electric field above a certain threshold provokes turbulent states denoted DSM1 and DSM2. While DSM1 does not affect the anchoring, DSM2 breaks the coupling between the surface and the liquid crystal: switching off the field from a DSM2 state does not immediately restore the homeotropic alignment. Instead, we obtain a quasi-planar metastable alignment. The cell thickness dependence for the transition is related to theComment: 7 pages, LaTeX2e article, 4 figures, 7 EPS files, added references, accepted for publication in Europhysics Letter

Asymptotics of Regulated Field Commutators for Einstein-Rosen Waves

We discuss the asymptotic behavior of regulated field commutators for linearly polarized, cylindrically symmetric gravitational waves and the mathematical techniques needed for this analysis. We concentrate our attention on the effects brought about by the introduction of a physical cut-off in the study of the microcausality of the model and describe how the different physically relevant regimes are affected by its presence. Specifically we discuss how genuine quantum gravity effects can be disentangled from those originating in the introduction of a regulator.Comment: 9 figures, 19 pages in DIN A4 format. Accepted for publication in Journal of Mathematical Physic

Windsurf: trying to stay afloat in water and in life

Desde una óptica biográfico-narrativa, este artículo gira en torno a Moisés, un profesional del campo de la Actividad Física Educativa, Recreativa y Deportiva (AFERD) que, a pesar de sus limitadas habilidades natatorias, ha dedicado buena parte de su vida al windsurf. Los objetivos se ciñen, primero, a reconstruir su trayectoria vital en relación con la natación y el windsurf y, segundo, a interpretar su biografía a partir del contexto y condicionantes sociales en que se desarrolla. Metodológicamente hemos utilizado, entre otros, la entrevistas narrativa, la semi-estructurada y el relato autobiográfico por encargo. Tras desglosar la biografía de Moisés se argumenta y concluye una mejor comprensión a partir de ciertos conceptos (habitus, identidad deportiva y espacio-cultura-estilo-de-vida distintivo) que permiten relacionar lo ‘personal’ con lo ‘social’. Moisés asume todo lo que aquí se dice y, además, nos ha sugerido el título del artículo.From a biographical narrative perspective, this paper focuses on Moses, a professional of the field of Physical Activity in Education, Leisure and Sports (AFERD) who, despite his very limited swimming skills, has devoted much of his life to windsurfing. The two objectives are: first, the reconstruction of Moses’ biography in relation to swimming and windsurfing and, second, the interpretation of such biography taking into account its context and conditions of existence. Methods used, among others, are: narrative interviews, semi-structured interviews and assigned autobiographical essays. Having analysed Moses’ biography, it’s argued that it is best understood by using some concepts (habitus, athletic identity and distinctive space-culture-and-life-style) that allows us to relate the ‘personal’ to the ‘social’. Moses accepts our explanations and, furthermore, he suggests the paper’s title

Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)2_2(ClO4_4)2_2

Cu(pz)$_2$(ClO$_4$)$_2$ (with pz denoting pyrazine C$_4$H$_4$N$_2$) is a two-dimensional spin-1/2 square-lattice antiferromagnet with $T_{\mathrm{N}}$ = 4.24 K. Due to a persisting focus on the low-temperature magnetic properties, its room-temperature structural and physical properties caught no attention up to now. Here we report a study of the structural features of Cu(pz)$_2$(ClO$_4$)$_2$ in the paramagnetic phase, up to 330 K. By employing magnetization, specific heat, $^{35}$Cl nuclear magnetic resonance, and neutron diffraction measurements, we provide evidence of a second-order phase transition at $T^{\star}$ = 294 K, not reported before. The absence of a magnetic ordering across $T^{\star}$ in the magnetization data, yet the presence of a sizable anomaly in the specific heat, suggest a structural order-to-disorder type transition. NMR and neutron-diffraction data corroborate our conjecture, by revealing subtle angular distortions of the pyrazine rings and of ClO$^-_4$ counteranion tetrahedra, shown to adopt a configuration of higher symmetry above the transition temperature.Comment: 10 pages, 12 figure