Properties of dirty two-bands superconductors with repulsive interband interaction: normal modes, length scales, vortices and magnetic response

Disorder in two-band superconductors with repulsive interband interaction induces a frustrated competition between the phase-locking preferences of the various potential and kinetic terms. This frustrated interaction can result in the formation of an $s+is$ superconducting state, that breaks the time-reversal symmetry. In this paper we study the normal modes and their associated coherence lengths in such materials. We especially focus on the consequences of the soft modes stemming from the frustration and time-reversal-symmetry breakdown. We find that two-bands superconductors with such impurity-induced frustrated interactions display a rich spectrum of physical properties that are absent in their clean counterparts. It features a mixing of Leggett's and Anderson-Higgs modes, and a soft mode with diverging coherence length at the impurity-induced second order phase transition from $s_{\pm}/s_{++}$ states to the $s+is$ state. Such a soft mode generically results in long-range attractive intervortex forces that can trigger the formation of vortex clusters. We find that, if such clusters are formed, their size and internal flux density have a characteristic temperature dependence that could be probed in muon-spin-rotation experiments. We also comment on the appearance of spontaneous magnetic fields due to spatially varying impurities.Comment: Added discussion of spontaneous magnetic fields due to spatially varying impurities; Replaced with a version in print in Phys. Rev. B; 17 pages, 8 figure

Recording the Learning Curve during the Mastery of Glassblowing

Fire and inspiration melted glass art’s enchanting ways into the center of my passions. Lampworking is a small-scale method of glass blowing, which is the term to refer to an art form where one shapes molten glass into a variety of items. To create glass art, propane and oxygen supply a flame torch which melts the glass. Gravity and rhythmic hands work symbiotically to shape glass rods and tubes. The result is unique three-dimensional visual art.After years of aspiring to work with borosilicate glass, the opportunity to incorporate the endeavor with academia presented itself. Through months of time and dedication, I was able to connect glass art with psychology by monitoring and recording the learning curve of a novice lampworker. Simply defined, a learning curve is a graphical representation of the increase of Learning or Proficiency (Vertical axis) with Experience (Horizontal axis.)Beginning with my first time using a torch, I kept a journal of my daily experiences, advancements, and accomplishments over the course of 14 weeks. This journal allowed me to observe the increase of knowledge and skills gained over time. Photographic and physical items were collected to provide a visual display of lampworking progress. To conclude my observation period, I constructed a final piece of psychology-inspired artwork that incorporated my highest levels of skills at the time.This project inspired me to question and observe some of the psychological processes related to art creation. It allowed me to discover and immerse myself in a mental state of flow, which involves full-capacity engagement in a goal-driven task. Tranquility, focus, challenge-skill balance, and control are some factors that accompany the flow of glasswork. The project also provided me with the basic skills I need to become an advanced glassworker. Through my involvement, I have acquired a true grasp on the value of working with one’s hands

Spin-Space Groups and Magnon Band Topology

Band topology is both constrained and enriched by the presence of symmetry. The importance of anti-unitary symmetries such as time reversal was recognized early on leading to the classification of topological band structures based on the ten-fold way. Since then, lattice point group and non-symmorphic symmetries have been seen to lead to a vast range of possible topologically nontrivial band structures many of which are realized in materials. In this paper we show that band topology is further enriched in many physically realizable instances where magnetic and lattice degrees of freedom are wholly or partially decoupled. The appropriate symmetry groups to describe general magnetic systems are the spin-space groups. Here we describe cases where spin-space groups are essential to understand the band topology in magnetic materials. We then focus on magnon band topology where the theory of spin-space groups has its simplest realization. We consider magnetic Hamiltonians with various types of coupling including Heisenberg and Kitaev couplings revealing a hierarchy of enhanced magnetic symmetry groups depending on the nature of the lattice and the couplings. We describe, in detail, the associated representation theory and compatibility relations thus characterizing symmetry-enforced constraints on the magnon bands revealing a proliferation of nodal points, lines, planes and volumes.Comment: 30 pages, 7 figure

Appearance of quasiperiodicity within a period doubling route to chaos of a swaying thermal plume

The birth, evolution and disappearance of quasiperiodic dynamics in buoyancy-driven flow arising from an enclosed horizontal cylinder are analysed here, by numerical means, in the limit of the 2D approximation. The governing equations are solved on orthogonal Cartesian grids, giving special treatment to the internal, non-aligned boundaries. Thanks to the adoption of a high level of re finement of the Rayleigh number range, quasiperiodicity was observed to emerge from a periodic limit cycle (P1), and to turn into its omologous orbit with doubled period (P2), eventually evolving into a classical period-doubling route to chaos, for further increases of the Rayleigh number. The present study gives a deeper insight to what appears to be an imperfect period doubling bifurcation through a quasiperiodic T2-torus. The approach used is based on the classical tools for time series analysis. The distribution of the power spectral densities is used to search for and characterise the existence of relations between the frequencies of the P1, T2 and P2 dynamics. The topology of the orbits, as well as their evolution within the quasiperiodic window, are analysed with the aid of phase space representation and Poincar è maps

Multi-Criteria Analysis and Decision-Making Approach for the Urban Regeneration: The Application to the Rimini Canal Port (Italy)

In recent decades, urban settlements have been greatly affected by globalisation, climate change, and economic uncertainty. When designing cities, these factors should be taken into account and adapted to the different contexts involved. The redevelopment of degraded urban areas is the first step toward achieving the sustainability aims set out in the Sustainable Development Goals. In this context, evaluation methods are required in the decision-making process, considering different social, economic, and environmental aspects to define the correct policies and actions for city redevelopment. In this paper, an evaluation methodology is proposed in order to obtain a priority scale of interventions for urban regeneration. Starting from on-site inspections to better know the current scenario, a set of indicators is established to evaluate the urban quality. Criticalities and potentials emerge through SWOT analysis and, with the ANP-BOCR method, the priority scale of the identified scenarios is defined. This decision-making approach was applied to the case study of the Rimini Canal Port, in the northeast of Italy, which is a degraded area of the city. This methodology is a tool that can be used in the future by decision makers (DMs) for the redevelopment of small port areas within similar urban contexts

The Spin Point Groups and their Representations

The spin point groups are finite groups whose elements act on both real space and spin space. Among these groups are the magnetic point groups in the case where the real and spin space operations are locked to one another. The magnetic point groups are central to magnetic crystallography for strong spin-orbit coupled systems and the spin point groups generalize these to the intermediate and weak spin-orbit coupled cases. The spin point groups were introduced in the 1960's and enumerated shortly thereafter. In this paper, we complete the theory of spin point groups by presenting an account of these groups and their representation theory. Our main findings are that the so-called nontrivial spin point groups (numbering 598 groups) have co-irreps corresponding exactly to the (co-)irreps of regular or black and white groups and we tabulate this correspondence for each nontrivial group. However a total spin group, comprising the product of a nontrivial group and a spin-only group, has new co-irreps in cases where there is continuous rotational freedom. We provide explicit co-irrep tables for all these instances. We also discuss new forms of spin-only group extending the Litvin-Opechowski classes. To exhibit the usefulness of these groups to physically relevant problems we discuss a number of examples from electronic band structures of altermagnets to magnons.Comment: 99 pages, 73 figures (mostly tables

Heat transfer along the route to chaos of a swaying thermal plume

Detailed analyses have been recently reported on the low order dynamics of a thermal plume arising from a horizontal cylindrical heat source concentric: to an air-\ufb01lled isothermally cooled square enclosure, together with those of the related \ufb02ow structures, in the limit of the 2D approximation. In particular. within the range of O < Ra < 3 RaL-T, With Ram corresponding to the loss of stability of the stationary buoyant plume, the entire evolution from a periodic limit cycle (P1) to the birth of chaos through a period\ubbdoubling cascade has been fullyexplored. With this respect, special attention has been given to the window of quasiperiodic dynamics onto a T;-torus that is observed to separate the monoperiodic dynamics from the biperiodic dynamics onto a P1 and a Pg-liniit cycle, respectively. The results of these analyses hint at the bimodal nature of the overall dynamics. in general, and of the subharmonic cascade, in particular, which are still under investigation. Although relevant on a dynamical perspective, a with a main re\ufb02ection on the laminar-turbulent transition, the observed oscillations appear to be characterised by comparable amplitudes and to be determined by similar evolutions of the \ufb02ow pattern evolutions, so that their role on the overall heat transfer rate is expected to be marginal. Vi/'ithin this frame, the present study aims at reporting the in\ufb02uence played by the observed dynamics of the thermal plume and of the [low structures on the global heat transferrate. In particular, the aim is the assessment of the correlation between the Rayleigh number and the average Nusselt number on the cylinder surface, as well as the effect on the latter of the observed series of bifurcations

Single-step preparation of inverse opal titania films by the doctor blade technique

The difficulty to infiltrate solid-state hole semiconductors within micron-thick porous titania films is one of the major limiting factors for the achievement of efficient solid-state dye-sensitized solar cells. It was already shown that through the ordered interconnected pores of an inverse opal, the large surface area of several microns thick titania film can be easily decorated with a dye and filled with a solid-state hole semiconductor. In this paper, we show that ordered inverse opal mesoporous thick films of TiO2 with these characteristics can be obtained by using a slurry of monodispersed polystyrene spheres and a titania-lactate precursor deposited by the doctor blade technique. The mechanism of formation of the inverse opal is also discussed

A fast algorithm for Direct Numerical Simulation of natural convection flows in arbitrarily-shaped periodic domains

A parallel algorithm is presented for the Direct Numerical Simulation of buoyancy-induced flows in open or partially confined periodic domains, containing immersed cylindrical bodies of arbitrary cross-section. The governing equations are discretized by means of the Finite Volume method on Cartesian grids. A semi-implicit scheme is employed for the diffusive terms, which are treated implicitly on the periodic plane and explicitly along the homogeneous direction, while all convective terms are explicit, via the second-order Adams-Bashfort scheme. The contemporary solution of velocity and pressure fields is achieved by means of a projection method. The numerical resolution of the set of linear equations resulting from discretization is carried out by means of efficient and highly parallel direct solvers. Verification and validation of the numerical procedure is reported in the paper, for the case of flow around an array of heated cylindrical rods arranged in a square lattice. Grid independence is assessed in laminar flow conditions, and DNS results in turbulent conditions are presented for two different grids and compared to available literature data, thus confirming the favorable qualities of the method