Spin-symmetric solution of an interacting quantum dot attached to superconducting leads: Andreev states and the 0−π0-\pi transition

Behavior of Andreev gap states in a quantum dot with Coulomb repulsion symmetrically attached to superconducting leads is studied via the perturbation expansion in the interaction strength. We find the exact asymptotic form of the spin-symmetric solution for the Andreev states continuously approaching the Fermi level. We thereby derive a critical interaction at which the Andreev states at zero temperature merge at the Fermi energy, being the upper bound for the $0-\pi$ transition. We show that the spin-symmetric solution becomes degenerate beyond this interaction, in the $\pi$ phase, and the Andreev states do not split unless the degeneracy is lifted. We further demonstrate that the degeneracy of the spin-symmetric state extends also into the $0$ phase in which the solutions with zero and non-zero frequencies of the Andreev states may coexist.Comment: 12 pages, 4 figure

Universality of vertex corrections to the electrical conductivity in models with elastically scattered electrons

We study quantum coherence of elastically scattered lattice fermions. We calculate vertex corrections to the electrical conductivity of electrons scattered either on thermally equilibrated or statically distributed random impurities. We demonstrate that the sign of the vertex corrections to the Drude conductivity is in both cases negative. Quantum coherence due to elastic back-scatterings always leads to diminution of diffusion.Comment: ReVTEX, 9 pages, 8 EPS figure

A response to the comment on the article: Plant—insect interactions … (Pokorný and Borges, 2023), by Góis‐Marques, Madeira and Menezes de Sequeira

ABSTRACT: We gratefully appreciate the comments made by Carlos A. Góis‐Marques, José Madeira and Miguel Menezes de Sequeira (hereafter CAG‐M et al.) on our recent paper in the Journal of Quaternary Science (Pokorný and Borges, 2023). We would like to respond regarding the content and partly also the tone of their comments. We were surprised that CAG‐M et al. chose this means of communication given that they were involved in the early stages of the work and that they declined the offer of co‐authorship. We clearly acknowledged this help at the end of our article. We first note that many of the specific c riticisms and irregularities reported by CAG‐M et al. focus excessively on written formulations and expressions, or comment on information taken from the literature that could not be verified. For the most part, we are able to refute the objections of CAG‐M et al. Where we agree with them, we present revised wording here, highlighted in bold type.info:eu-repo/semantics/publishedVersio

Plant–insect interactions in the Quaternary fossil record of the Azores Archipelago (Portugal)

ABSTRACT: The fossil record of the Azores still lacks evidence of terrestrial invertebrates. Based on a study of the collections of Quaternary fossil plant imprints from the Azores, located in the depositories of public collections and also newly conducted field research, several samples of fossil leaves with traces of plant–animal interactions were found. These are evidence of marginal feeding (Phagophytichnus ekowskii) and anophionome mine (Cuniculonomus isp.). One specimen with traces of boring in fossil wood (Xylonichnus trypetus), previously only briefly mentioned in the literature, was also described in detail. In addition to a detailed description of the found traces, the present study also discusses the possible trace-makers, using a comparison with the recent phytophagous fauna in relation to the original vegetation of the Azores (that includes laurisilva forest). It is thus possible to consider butterfly caterpillars (group Macrolepidoptera) or locust larvae (Orthoptera/Caelifera) as possible originators of marginal feeding. The ophionome mine could have been caused by the larvae of leaf-miner flies (Agromyzidae) or moths from the group Microlepidoptera (Gracillariidae). Wood-destroying beetles could be the cause of the boring in fossil wood.info:eu-repo/semantics/publishedVersio

Vertex Corrections to the Electrical Conductivity of the Disordered Falicov-Kimball Model

Quantum coherence of elastically scattered lattice fermions is studied. We calculate vertex corrections to the electrical conductivity of electrons scattered either on thermally equilibrated or statically distributed random impurities and we demonstrate that the sign of the vertex corrections to the Drude conductivity is in both cases negative. PACS numbers: 71.10. Fd, 71.28.+d, 72.10.Fk Model The Coulomb interactions and disorder can individually result in a metal-insulator transitions (MIT). It is not much known how this transition is modified when both forces act simultaneously. It is the aim of this contribution to investigate such a situation when only elastic scatterings are taken into account. We consider the disordered Falicov-Kimball model (FKM) described by the following Hamiltonian: where c † i (c i ) represents a creation (annihilation) operator of an itinerant electron on site i and f † i (f i ) represents a creation (annihilation) operator for an electron localised on site i. We denoted by t the nearest-neighbor hopping amplitude for itinerant electrons, U is the interaction strength between the itinerant and localised electrons and finally V i is the on-site random atomic potential with a static site-independent probability distribution P(V ). For U = 0 the Hamiltonian (1) reduces to the disordered Anderson model. For V i = 0 we recover the pure Falicov-Kimball model that can be interpreted as a model of electrons scattered on thermally equilibrated impurities where U represents the strength of a dynamic (annealed) disorder. The exact solution for the FKM is known in d = ∞ limit and the equilibrium thermodynamics as well as transport properties were reviewed in The method for calculating vertex corrections to the one-electron Drude conductivity for models with elastically scattered electrons was recently developed by us Results and discussion We evaluated numerically only the leading 1/d-order vertex correction to the Drude zero-temperature conductivity from Ref. where ∆ is the measure of disorder strength. For explicit calculations we use a semi-elliptic density of states ρ(ε) = 2/π √ 1 − ε 2 and set the spatial dimension d = 3. We neglect the chess-board long-range order of the pure model, since the ground state is then insulating. The Drude conductivity σ 0 , total conductivity σ 0 +∆σ and the density of states at the Fermi energy ρ F for U = 0.5 are plotted i

Nanostrukturalno oblikovanje jakom plastičnom deformacijom

The influence of severe plastic deformations on structural, mechanical and plastic properties of ARMCO-Fe in equal-channel angular pressing procedure was investigated. Mathematical simulations of stress and temperature fields were applied, too.Istraživao se utjecaj snažnih plastičnih deformacija na strukturalna, mehanička i plastična svojstva ARMCO-željeza u postupku prešanja s istiskivanjem kroz jednake kanale (ECAP) postavljene pod nekim kutom. Primjenjivale su se također i matematičke simulacije područja naprezanja i temperaturnih područja

LiBC by polarized Raman spectroscopy: Evidence for lower crystal symmetry ?

The paper presents polarized Raman scattering study on a few-micron-size crystallite of LiBC with natural faces. The experiment on as grown sample has revealed a four lattice modes with frequencies at 1276 cm^-1, 830 cm^-1, 546 cm^-1 and 170 cm^-1, respectively. The number of observed Raman lines and their selection rules are incompatible with the assumed D6h symmetry. The modes at 1276 cm^-1 and 170 cm^-1 correspond to the expected Raman active modes. In contrast with the superconducting compound MgB2, the B-C bond stretching mode (at 1276 cm^-1) has rather small damping. The two "forbidden" modes (at 830 cm^-1 and 546 cm^-1) disappeared after subsequent thermal treatment.Comment: 4 pages, LaTeX, complementary experimental resul

Use of cement suspension as an alternative matrix material for textile-reinforced concrete

Textile-reinforced concrete (TRC) is a material consisting of high-performance concrete (HPC) and tensile reinforcement comprised of carbon roving with epoxy resin matrix. However, the problem of low epoxy resin resistance at higher temperatures persists. In this work, an alternative to the epoxy resin matrix, a non-combustible cement suspension (cement milk) which has proven stability at elevated temperatures, was evaluated. In the first part of the work, microscopic research was carried out to determine the distribution of particle sizes in the cement suspension. Subsequently, five series of plate samples differing in the type of cement and the method of textile reinforcement saturation were designed and prepared. Mechanical experiments (four-point bending tests) were carried out to verify the properties of each sample type. It was found that the highest efficiency of carbon roving saturation was achieved by using finer ground cement (CEM 52.5) and the pressure saturation method. Moreover, this solution also exhibited the best results in the four-point bending test. Finally, the use of CEM 52.5 in the cement matrix appears to be a feasible variant for TRC constructions that could overcome problems with its low temperature resistance