Multivalued current-phase relationship in a.c. Josephson effect for a three-dimensional Weyl semimetal WTe2_2

We experimentally study electron transport between two superconducting indium leads, coupled to a single WTe$_2$ crystal, which is a three-dimensional Weyl semimetal. We demonstrate Josephson current in long 5~$\mu$m In-WTe$_2$-In junctions, as confirmed by the observation of integer (1,2,3) and fractional (1/3, 1/2, 2/3) Shapiro steps under microwave irradiation. Demonstration of fractional a.c. Josephson effect indicates multivalued character of the current-phase relationship, which we connect with Weyl topological surface states contribution to Josephson current. In contrast to topological insulators and Dirac semimetals, we do not observe $4\pi$ periodicity in a.c. Josephson effect for WTe$_2$ at different frequencies and power, which might reflect chiral character of the Fermi arc surface states in Weyl semimetal.Comment: the text is seriously corrected. arXiv admin note: text overlap with arXiv:1801.0955

The main directions for pharmacological correction (combinations of drugs for general anesthesia) of neurological and cognitive disorders in patients with neoplasms of the central nervous system

The aim of the study was to develop a goal-oriented combination of drugs for general anesthesia, based on a retrospective assessment of the baseline level of neurological and cognitive disorders in adults and children at the stage of preparation for surgery for neoplasms of the central nervous system (sub- and supratentorial neoplasms - SubTNN and SupraTNN), and a prospective evaluation of complications in the postoperative perio

Dissolution, Reactor, and Environmental Behavior of ZrO2-MgO Inert Fuel Matrix: Neutronic Evaluation of ZrO2-MgO Inert Fuels

This report presents the results of the Task 3, defined in working program as: evaluation of burnable poison designs. Adopting the basic design of a standard PWR and Pu loadings required for 18-month cycle (results of Task 2), this part of the program is aimed to estimate performance of each BP design and BP material to address challenges of Fertile-Free Fuel (FFF) Concept. Finally, an optimal BP design will be developed and an overall feasibility of FFF concept will be determined. Basically, the main challenge encountered in neutronic design for a FFF core is to develop reactivity control system which is capable to satisfy performance and safety criteria of existing PWR plants. Heavy Pu loadings combined with absence of fertile isotopes with capture resonances result in low reactivity worth of existing control mechanisms and inadequate temperature coefficients. The main solution adopted by several previous design efforts is based on increased content of BP materials with capture resonances. The BP designs proposed and analyzed in previous designs are based on such elements as: Gd, Hf, and Er, located in fuel cell, either as a homogeneous mixture or as a thin ring (IFBA-type geometry). This approach results in a large residual reactivity penalty due to an incomplete burnup of the BP material (especially Hf and Er). Description and parameters of the BP designs considered in this work are presented in section II. In this report, an extensive set of calculations was carried out to assess the potential of the main BP materials - B, Gd, Hf, and Er, utilized in three main geometrical arrangements: Wet Annular Burnable Absorber (WABA) type, Integral Fuel Burnable Absorber (IFBA) type, and Homogeneous fuel-BP mixture. Heavy loadings of BP materials in non-standard geometries combined with high Pu content in a fertile-free matrix necessitated additional verification of the calculational tools. Verification of the calculational modeling and parameters are presented in section III. A full scope of calculations is presented in section IV of this report. All cases are arranged according to geometry-type and BP material. The results and analysis of these calculations, presented and summarized in Section V, serve as a basis for a comprehensive assessment of BP potential to address challenges of the FFF concepts. Three main performance parameters of the BP designs will be evaluated: 1. Maximum critical soluble boron concentration (CBC) required during the cycle, 2. Acceptable fuel and moderator temperature coefficients (will be evaluated in Task 4), 3. Residual reactivity penalty associated with incomplete depletion of the BP materia

Interface states in junctions of two semiconductors with intersecting dispersion curves

A novel type of shallow interface state in junctions of two semiconductors without band inversion is identified within the envelope function approximation, using the two-band model. It occurs in abrupt junctions when the interband velocity matrix elements of the two semiconductors differ and the bulk dispersion curves intersect. The in-plane dispersion of the interface state is found to be confined to a finite range of momenta centered around the point of intersection. These states turn out to exist also in graded junctions, with essentially the same properties as in the abrupt case.Comment: 1 figur

Signature of Fermi arc surface states in Andreev reflection at the WTe2_2 Weyl semimetal surface

We experimentally investigate charge transport through the interface between a niobium superconductor and a three-dimensional WTe$_2$ Weyl semimetal. In addition to classical Andreev reflection, we observe sharp non-periodic subgap resistance resonances. From an analysis of their positions, magnetic field and temperature dependencies, we can interpret them as an analog of Tomasch oscillations for transport along the topological surface state across the region of proximity-induced superconductivity at the Nb-WTe$_2$ interface. Observation of distinct geometrical resonances implies a specific transmission direction for carriers, which is a hallmark of the Fermi arc surface states.Comment: 5 pages, some misprints has been correcte

Multiple magnon modes in the Co3_3Sn2_2S2_2 Weyl semimetal candidate

We experimentally investigate electron transport in kagome-lattice ferromagnet Co$_3$Sn$_2$S$_2$, which is regarded as a time-reversal symmetry broken Weyl semimetal candidate. We demonstrate $dV/dI(I)$ curves with pronounced asymmetric $dV/dI$ spikes, similar to those attributed to current-induced spin-wave excitations in ferromagnetic multilayers. In contrast to multilayers, we observe several $dV/dI$ spikes' sequences at low, $\approx$10$^4$ A/cm$^2$, current densities for a thick single-crystal Co$_3$Sn$_2$S$_2$ flake in the regime of fully spin-polarized bulk. The spikes at low current densities can be attributed to novel magnon branches in magnetic Weyl semimetals, which are predicted due to the coupling between two magnetic moments mediated by Weyl fermions. Presence of spin-transfer effects at low current densities in Co$_3$Sn$_2$S$_2$ makes the material attractive for applications in spintronics.Comment: final versio