Tunneling between two systems of interacting chiral fermions

We develop a theory of tunneling between two systems of spinless chiral fermions. This setup can be realized at the edge of a quantum Hall bilayer structure. We find that the differential conductance of such a device in the absence of interactions has an infinitely sharp peak as a function of applied voltage. Interaction between fermions results in broadening of the conductance peak. We focus on the regime of strong interactions, in which the shape of the peak manifests well defined features associated with the elementary excitations of the system.Comment: 12 page

Physics of the Majorana-superconducting qubit hybrids

Manipulation of decoupled Majorana zero modes (MZMs) could enable topologically-protected quantum computing. However, the practical realization of a large number of perfectly decoupled MZMs needed to perform nontrivial quantum computation has proven to be challenging so far. Fortunately, even a small number of imperfect MZMs can be used to qualitatively extend the behavior of standard superconducting qubits, allowing for new approaches for noise suppression, qubit manipulation and read-out. Such hybrid devices take advantage of interplay of Cooper pair tunneling, coherent single electron tunneling, and Majorana hybridization. Here we provide a qualitative understanding of this system, give analytical results for its ground state energy spanning full parameter range, and describe potential sensing applications enabled by the interplay between Majorana and Cooper pair tunneling.Comment: 13 page

Structural and Physical Properties of CaFe4As3 Single Crystals

We report the synthesis, and structural and physical properties of CaFe4As3 single crystals. Needle-like single crystals of CaFe4As3 were grown out of Sn flux and the compound adopts an orthorhombic structure as determined by X-ray diffraction measurements. Electrical, magnetic, and thermal properties indicate that the system undergoes two successive phase transitions occurring at TN1 ~ 90 K and TN2 ~ 26 K. At TN1, electrical resistivities (\rho(b) and \rho(ac)) are enhanced while magnetic susceptibilities (\chi(b) and \chi(ac)) are reduced in both directions parallel and perpendicular to the b-axis, consistent with the scenario of antiferromagnetic spin-density-wave formation. At TN2, specific heat reveals a slope change, and \chi(ac) decreases sharply but \chi(b) has a clear jump before it decreases again with decreasing temperature. Remarkably, both \rho(b) and \rho(ac) decrease sharply with thermal hysteresis, indicating the first-order nature of the phase transition at TN2. At low temperatures, \rho(b) and \rho(ac) can be described by {\rho} = {\rho}0 + AT^\alpha ({\rho}0, A, and {\alpha} are constants). Interestingly, these constants vary with applied magnetic field. The ground state of CaFe4As3 is discussed.Comment: 15 pages, 8 figures, Submitted to Physical Review

Interrogating the superconductor Ca10(Pt4As8)(Fe2-xPtxAs2)5 Layer-by-layer

Ever since the discovery of high-Tc superconductivity in layered cuprates, the roles that individual layers play have been debated, due to difficulty in layer-by-layer characterization. While there is similar challenge in many Fe-based layered superconductors, the newly-discovered Ca10(Pt4As8)(Fe2As2)5 provides opportunities to explore superconductivity layer by layer, because it contains both superconducting building blocks (Fe2As2 layers) and intermediate Pt4As8 layers. Cleaving a single crystal under ultra-high vacuum results in multiple terminations: an ordered Pt4As8 layer, two reconstructed Ca layers on the top of a Pt4As8 layer, and disordered Ca layer on the top of Fe2As2 layer. The electronic properties of individual layers are studied using scanning tunneling microscopy/spectroscopy (STM/S), which reveals different spectra for each surface. Remarkably superconducting coherence peaks are seen only on the ordered Ca/Pt4As8 layer. Our results indicate that an ordered structure with proper charge balance is required in order to preserve superconductivity

Spin-Orbit Scattering and Quantum Metallicity in Ultra-Thin Be Films

We compare and contrast the low temperature magnetotransport properties of ultra-thin, insulating, Be films with and without spin-orbit scattering (SOS). Beryllium films have very little intrinsic SOS, but by "dusting" them with sub-monolayer coverages of Au, one can introduce a well controlled SOS rate. Pure Be films with sheet resistance R >R_Q exhibit a low-temperature negative magnetoresistance (MR) that saturates to the quantum resistance R_Q = h/e^2. This high-field quantum metal phase is believed to represent a new ground state of the system. In contrast, the corresponding negative MR in Be/Au films is greatly diminished, suggesting that, in the presence of strong SOS, the quantum metal phase can only be reached at field scales well beyond those typically available in a low temperature laboratory.Comment: 12 pages, 4 figures, to appear in PR

NaV2O4: a Quasi-1D Metallic Antiferromagnet with Half-Metallic Chains

NaV2O4 crystals were grown under high pressure using a NaCl flux, and the crystals were characterized with X-ray diffraction, electrical resistivity, heat capacity, and magnetization. The structure of NaV2O4 consists of double chains of edge-sharing VO6 octahedra. The resistivity is highly anisotropic, with the resistivity perpendicular to the chains more than 20 times greater than that parallel to the chains. Magnetically, the intrachain interactions are ferromagnetic and the interchain interactions are antiferromagnetic; 3D antiferromagnetic order is established at 140 K. First principles electronic structure calculations indicate that the chains are half metallic. Interestingly, the case of NaV2O4 seems to be a quasi-1D analogue of what was found for half-metallic materials.Comment: 14 pages, including 4 figures and 1 table, accepted for publication in PR

Influenza and pneumococcal vaccination in Australian adults: A systematic review of coverage and factors associated with uptake

© 2016 The Author(s). Background: In the absence of an adult vaccination register, coverage estimates for influenza and pneumococcal vaccination come from surveys and other data sources. Methods: Systematic review and meta-analysis of studies examining vaccination coverage in Australian adults from 1990 to 2015, focusing on groups funded under the National Immunisation Program, and intervals prior to and following the introduction of universal funding. Results: Twenty-two studies met the inclusion criteria; 18 used self-report to determine vaccination status. There were 130 unique estimates of coverage extracted. Among adults aged ≥65y, during the period of universal funding (1999-onwards), the summary estimate of annual influenza vaccination coverage from 27 point estimates was 74.8 % (95 % CI 73.4-76.2 %; range 63.9-82.4 %); prior to this period (1992-1998) from 10 point estimates it was 61.3 % (95 % CI 58.0-64.6 %; range 44.3-71.3 %). For the period of universal funding for pneumococcal vaccination (2005-onwards) the summary estimate for coverage was 56.0 % (95 % CI 53.2-58.8 %; range 51.2-72.8 %, 10 point estimates); prior to 2005 it was 35.4 % (95 % CI 18.8-52.0 %; range 15.4-45.2 %). Coverage for both vaccines was significantly higher following the introduction of universal funding. Influenza vaccination coverage in those aged 18-65 years with a medical indication was lower but data were not combined. Seven studies reported on Aboriginal Australians with three studies reporting five coverage estimates for influenza vaccination in adults ≥65 years (range 71 % - 89 %). Conclusions: Adult influenza and pneumococcal vaccination coverage has increased since the introduction of universal funding, but remains sub-optimal, with pneumococcal coverage lower than influenza. Implications: This review highlights the need for more coverage data overall and in high risk groups, to support public health programs to improve coverage