Dimensional Junction Research Articles

Improvement of a diffusion-based microfluidic chemotaxis assay through stable formation of a chemical gradient

Microfluidic chemotaxis analysis requires stable and reproducible formation of chemical gradient with low batch-to-batch variation. Dimensional uniformity of a junction channel plays a key role in diffusion-based gradient generation. Conventional methods for the analysis of bacterial chemotaxis are limited in stability and reproducibility of the chemical gradient. Here, we report a microfabrication method employing plasma enhanced chemical vapor deposition for silicon oxide deposition and consecutive reactive ion etching processes to reduce the experimental errors of chemotaxis analysis occurring from dimensional inaccuracy of the junction channel. This approach produces precise dimensional junction channels with below 1% variation. Thus, we confirm the reproducibility of chemotaxis analysis and obtain the chemotaxis index of Pseudomonas aeruginosa PAO1 with bacterial chemoeffectors.

Majorana zero modes in spintronics devices

We show that topological phases should be realizable in readily available and well studied heterostructures. In particular we identify a new class of topological materials which are well known in spintronics: helical ferromagnet-superconducting junctions. We note that almost all previous work on topological heterostructures has focused on creating Majorana modes at the proximity interface in effectively two-dimensional or one-dimensional systems. The particular heterostructures we address exhibit finite range proximity effects leading to nodal superconductors with Majorana modes localized well away from this interface. To show this, we implement a Bogoliubov-de Gennes (BdG) proximity numerical scheme, which importantly, involves two finite dimensions in a three dimensional junction. Incorporating this level of numerical complexity serves to distinguish ours from alternative numerical BdG approaches which are limited by generally assuming translational invariance or periodic boundary conditions along multiple directions. With this access to the edges, we are then able to illustrate in a concrete fashion the wavefunctions of Majorana zero modes, and, moreover, address finite size effects. In the process we establish consistency with a simple analytical model.

A diagrammatic approach to triplet supercurrents in ferromagnetic Josephson junctions

We present a numerical study of ferromagnetic Josephson junctions with one intermediate layer and spin active interfaces in the ballistic regime, comparing the behaviour of one, two and three dimensional junctions. We find that in two and three dimensional junctions the geometries which lack spin flip scattering at one of the interfaces have a critical current that decays to zero, as we increase the magnetization of the intermediate layer towards the half metal limit. As known, magnetization direction inhomogeneity produces a long range supercurrent with width variation, even when spin flip scattering exists in one of the interfaces only, although of lower characteristic decay length, compared to junctions with spin flip scattering at both interfaces. In the case of a single spin-flip interface and large thickness of the junction, we find a dominant second harmonic in the current-phase relation, in agreement with earlier work. We apply a diagrammatic approach, which explains the strong second harmonic and the long range property of the supercurrent. We find that in the three dimensional junction case the main contribution to both the long range supercurrent and the second harmonic in thick Josephson junctions with one spin flip interface comes from diagrammatic terms that correspond to scattering loops inside the junction which are subject to anomalous Andreev reflections on the spin flip interface and normal Andreev reflections at the non spin flip interface, thus exhibiting the triplet nature of the phenomenon. We also find the emergence of the strong first harmonic for small variation of the magnetization geometry and comment on the effect of normal interface scattering and temperature on the second harmonic.

Andreev reflection between a normal metal and the FFLO superconductor II: A self-consistent approach

We consider Andreev reflection in a two dimensional junction between a normal metal and a heavy fermion superconductor in the Fulde–Ferrell (FF) type of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state. We assume s-wave symmetry of the superconducting gap. The parameters of the superconductor: the gap magnitude, the chemical potential, and the Cooper pair center-of-mass-momentum Q, are all determined self-consistently within a mean-field (BCS) scheme. The Cooper pair momentum Q is chosen as perpendicular to the junction interface. We calculate the junction conductance for a series of barrier strengths. In the case of incoming electron with spin σ = ↑ only for magnetic fields close to the upper critical field H c2 , we obtain the so-called Andreev window, i.e. the energy interval in which the reflection probability is maximal, which in turn is indicated by a peak in the conductance. The last result differs with other non-self-consistent calculations existing in the literature.

TEM techniques for two dimensional junction delineation in integrated circuits : A. Romano, J. Vanhellemont, J. R. Morante and W. Vandervorst. Micron Microscop. Acta20(2), 151 (1989)

TEM techniques for two dimensional junction delineation in integrated circuits : A. Romano, J. Vanhellemont, J. R. Morante and W. Vandervorst. Micron Microscop. Acta20(2), 151 (1989)

TEM techniques for two dimensional junction delineation in integrated circuits

TEM techniques for two dimensional junction delineation in integrated circuits