No abstract available

[en] Transport properties in a quantum resonator structure of a normal-conductor endash superconductor (NS) junction are calculated. Quasiparticles in a cavity region undergo multiple reflections due to an abrupt change in the width of the wire and the NS interface. Quantum interference of the reflections modulates the nominal normal reflection probability at the NS boundary. We show that various NS structures can be regarded as the quantum resonator because of the absence of propagation along the NS interface. When the incident energy coincides with the quasibound state energy levels, the zero-voltage conductance exhibits peaks for small voltages applied to the NS junction. The transmission peaks change to dips of nearly perfect reflection when the applied voltage exceeds a critical value. Two branches of the resonance, which are roughly characterized by electron and hole wavelengths, emerge from the individual dip, and the energy difference between them increases with increasing voltage. The electronlike and holelike resonance dips originating from different quasibound states at zero-voltage cross one after another when the voltage approaches the superconducting gap. We find that both crossing and anticrossing can be produced. It is shown that the individual resonance state in the NS system is associated with two zeros and two poles in the complex energy plane. The behavior of the resonance is explained in terms of splitting and merging of the zero-pole pairs. We examine the Green close-quote s function of a one-dimensional NS system in order to find out how the transmission properties are influenced by the scattering from the NS interface. copyright 1996 The American Physical Society

[en] The helical edge states of two-dimensional topological insulators (TIs) experience appreciable quantum mechanical scattering in narrow channels when the width changes abruptly. The interference of the geometry scattering in narrow-wide-narrow waveguide structures is shown to give rise to the strong suppression of transmission when the incident energy is barely above the propagation threshold. Periodic resonant transmission takes place in this high reflection regime while the length of the wide section is varied. The resonance condition is governed by the transverse confinement in the wide section, where the form of quantization is manifested to differ for the two orthogonal directions. The confined energy levels in TI quantum dots are derived based on this observation. In addition, the off-diagonal spin-orbit term is found to produce an anomalous resonance state, which merges with the bottom ordinary resonance state to annihilate

[en] Interleukin 3 (IL3) has recently been shown to be a mast cell/basophil growth factor. Based on the previous observations that IL3-dependent cells are capable of NC activity which are believed to be important in immunosurveillance, the authors attempted to define if the IL3-dependent NC cells were of basophilic origin. To approach this, the authors tested a murine IL3-dependent basophilic cell line and a rat basophilic leukemic cell line against various tumor targets in a 4h or 18h ⁵¹Cr release assay. Both basophilic cell types effectively lysed the NC target, WEHI-164, but not the NK targets, YAC-1, RLM1, RBL5. Moreover, triggering of the basophils by incubation at 37C with IgE-anti-IgE or IgE with specific antigen or by direct binding to anti-IgE receptor antibodies enhanced NC activity and at the same time induced the release of a soluble cytotoxic factor (CF). The CF lysed only WEHI but not YAC-1, RLM1 or RBL5 tumor cells, distinguishing it from NKCF. The release of the NCCF was dependent on the dose of the triggering agents, required extracellular Ca⁺⁺, and was detected within 15 min of triggering. It has a MW of 43,000 as determined by gel filtration. Basophils, therefore, are not only involved in inflammatory responses but also in tumor immunity, via the NC effector mechanism

[en] The discontinuous change in the lattice constant that occurs at the first-order phase transition between α- and β-MnAs gives rise to a coexistence of the two phases in MnAs layers grown on GaAs substrates. When the GaAs substrates are oriented in the (111)B direction, the c axis of MnAs is aligned normal to the growth plane. We identify the domain structure of α- and β-MnAs for this crystal orientation by utilizing the different reactivities of the two phases against wet chemical etching. Submicrometer-size islands of α-MnAs are found to be interwoven in a honeycomblike network of β-MnAs. We also show that this domain structure combined with strain effects results in a formation of MnAs lumps by etching

[en] We demonstrate dipolar correlation in the orientation of magnetization in square arrays of MnAs nanodisks fabricated from epitaxial layers on GaAs(001). The MnAs(1100) layers possess strong in-plane uniaxial magnetocrystalline anisotropy, which enables us to discard microvortex-type ordering from degeneracy while maintaining the disks as circularly shaped with a small diameter. The autocorrelation function reveals antiferromagnetic collinear arrangements of the magnetic moments in the arrays both in the single-domain and flux-closure-state regimes of the disks. The interaction range is deduced to be nearly identical to the period of the arrays

[en] The quantum transmission of helical edge states across a square potential barrier is numerically investigated in narrow channels of a two-dimensional topological insulator. Although the transmission probability in general decreases when a potential offset is introduced in the middle of the channels, the transmission remains almost perfect regardless of the amplitude and length of the potential offset when the hybridization energy gap is closed by tuning the off-diagonal spin–orbit terms in the effective four-band Hamiltonian. The approximate absence of scattering resembling the Klein tunneling, where the transmission is unimpeded as an electron propagates relativistically as a hole in the barrier without decay, improves further when an interference condition is satisfied within the barrier. The dependence of the residual reflection on the Fermi level reveals anomalous characteristics in the Klein tunneling regime. (paper)

[en] Conductance modulations in wide-narrow-wide electron waveguides constructed from a two-dimensional topological insulator are investigated numerically. The conductance exhibits the Fabry-Perot oscillation at the opening of the helical edge states in the narrow segment when the potential offset imposed in the segment is varied. The quantum multiple reflections between the two ends of the narrow segment manifested by the oscillation demonstrate that the topological states are not protected from the scattering caused by an abrupt change in the channel width. The bulk states do not affect the vulnerability against the geometry scattering but they give rise to resonant transmission in an unconventional fashion.

[en] In our previous report (Takagaki et al 2011 Semicond. Sci. Technol. 26 085031), we have demonstrated that the Bi atoms in Bi₂Se₃ are substituted by the substrate atoms when its growth is attempted on the surface of transition metals using the hot-wall-epitaxy method. Here, we show that the substitution takes place similarly when Bi₂Te₃ and Sb₂Te₃ are employed as the source materials. For Ag, Cu and Ta substrates, Bi and Sb atoms are replaced completely, whereas the replacement is partial for Ni. Au induces no substitution and, on the contrary, helps to form Bi₂Te₃ and Sb₂Te₃ crystals at high temperatures. The lowering of the melting point of the substrate metals by inclusion of source elements causes some dependences of the growth outcome on the source materials. We also perform optical characterizations of the silver, copper and nickel tellurides synthesized by the substitution. (paper)

[en] We describe a growth procedure utilizing molecular beam epitaxy that produces a (1100)-oriented MnAs layer on GaAs(111)B despite the incompatible unit mesh symmetry. An amorphous MnAs layer is deposited at a low temperature beyond the critical thickness for coherent growth. When solid-phase epitaxy is initiated by reducing the background As₄ pressure, the layer crystalizes in the M-plane orientation with its c axis being along the (112) directions of the substrate. The magnetization components associated with the coexisting c-axis orientations are independent of each other, suggesting that the structural domains are much larger in size than the atomic scales