Using Josephson junctions to determine the pairing state of superconductors without crystal inversion symmetry

Theoretical studies of a planar tunnel junction between two superconductors with antisymmetric spin-orbit coupling are presented. The half-space Green's function for such a superconductor is determined. This is then used to derive expressions for the dissipative current and the Josephson current of the junction. Numerical results are presented in the case of the Rashba spin-orbit coupling, relevant to the much studied compound CePt$_3$Si. Current-voltage diagrams, differential conductance and the critical Josephson current are presented for different crystallographic orientations and different weights of singlet and triplet components of the pairing state. The main conclusion is that Josephson junctions with different crystallographic orientations may provide a direct connection between unconventional pairing in superconductors of this kind and the absence of inversion symmetry in the crystal.Comment: 16 pages, 10 figure

On a diffuse interface model for tumour growth with non-local interactions and degenerate mobilities

We study a non-local variant of a diffuse interface model proposed by Hawkins--Darrud et al. (2012) for tumour growth in the presence of a chemical species acting as nutrient. The system consists of a Cahn--Hilliard equation coupled to a reaction-diffusion equation. For non-degenerate mobilities and smooth potentials, we derive well-posedness results, which are the non-local analogue of those obtained in Frigeri et al. (European J. Appl. Math. 2015). Furthermore, we establish existence of weak solutions for the case of degenerate mobilities and singular potentials, which serves to confine the order parameter to its physically relevant interval. Due to the non-local nature of the equations, under additional assumptions continuous dependence on initial data can also be shown.Comment: 28 page

Optical pumping of charged excitons in unintentionally doped InAs quantum dots

As an alternative to commonly used electrical methods, we have investigated the optical pumping of charged exciton complexes addressing impurity related transitions with photons of the appropriate energy. Under these conditions, we demonstrate that the pumping fidelity can be very high while still maintaining a switching behavior between the different excitonic species. This mechanism has been investigated for single quantum dots of different size present in the same sample and compared with the direct injection of spectator electrons from nearby donors.Comment: 4 pages and 3 figures submitted to AP

Strong solutions to nonlocal 2D Cahn--Hilliard--Navier--Stokes systems with nonconstant viscosity, degenerate mobility and singular potential

We consider a nonlinear system which consists of the incompressible Navier-Stokes equations coupled with a convective nonlocal Cahn-Hilliard equation. This is a diffuse interface model which describes the motion of an incompressible isothermal mixture of two (partially) immiscible fluids having the same density. We suppose that the viscosity depends smoothly on the order parameter as well as the mobility. Moreover, we assume that the mobility is degenerate at the pure phases and that the potential is singular (e.g. of logarithmic type). This system is endowed with no-slip boundary condition for the (average) velocity and homogeneous Neumann boundary condition for the chemical potential. Thus the total mass is conserved. In the two-dimensional case, this problem was already analyzed in some joint papers of the first three authors. However, in the present general case, only the existence of a global weak solution, the (conditional) weak-strong uniqueness and the existence of the global attractor were proven. Here we are able to establish the existence of a (unique) strong solution through an approximation procedure based on time discretization. As a consequence, we can prove suitable uniform estimates which allow us to show some smoothness of the global attractor. Finally, we discuss the existence of strong solutions for the convective nonlocal Cahn-Hilliard equation, with a given velocity field, in the three dimensional case as well

Multiple slit interference and diffraction

The recent advances in nanotechnology and electron microscopy are making today possible the realization of experiments of diffraction and interference at multiple slits which formerly were carried out with extremely skilled specimen preparation techniques and dedicated electron optical apparatus [1]. Recently we have used the focused ion beam (FIB) to fabricate two slits on a commercial silicon nitride membrane suspended on a 100x100μm2 window realized on a 200μm thick silicon substrate, and observe the Fraunhofer image in a conventional TEM-JEOL 2010 [2]. Here we adopt a less expensive support for nano slits fabrication, consisting of a commercial continuous carbon film on a standard copper grid, which was subsequently evaporated with a gold layer about 120 nm in thickness. The slits (nominally 80nm wide, 420 nm spaced) were fabricated with a 9 pa, 30keV, Ga+ beam of a FEI Strata235M dual beam. The quality of the slits is really excellent, as shown in Fig. 1, which displays two (a), and three (b) slits. An additional advantage of these samples with respect to the previous 200μm thick ones, is that they can be inserted in almost all TEM-FEG specimen holder. The diffraction and interference experiments were carried out with the FEG-TEM JEM-2200FS. Owing to the larger coherence of the FEG with respect to the thermionic source, it has been possible to record interference and diffraction images with exposure times of few seconds. The three-slit case is illustrated in Fig. 2: (a) shows the image in focus, (b-d) the images taken at a nominal defocus of -10 mm, -20 mm and -40 mm respectively. They show the transition from the nearly separated Fresnel diffraction images of the single slits (b), to their subsequent overlapping as the defocus increases (c), displaying interference phenomena, till (d) the transition to a nearly Fraunhofer image. Fig. 3 displays the true Fraunhofer image, taken at a nominal defocus of -53 mm, which clearly shows the secondary minima between the more intense maxima. In the same in the perpendicular direction the single slit Fraunhofer images corresponding to the longer side of the slits can also be observed

97: Positron Emission Tomography Identifies a Differential Pattern of Bone Marrow FdG Uptake in "Poor" and "Good" Peripheral Stem Cell Mobilizers

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Modelling of broadband light sources based on InAs / INxGA1-xAS metamorphic quantum dots

We propose a design for a semiconductor structure emitting broadband light in the infrared, based on InAs quantum dots (QDs) embedded into a metamorphic 4-step-graded InxGa1- xAs buffer with x = 0.10, 0.20, 0.30, 0.40. We developed a model to calculate metamorphic QD energy levels based on realistic QD parameters and on strain-dependent material properties: results of simulations were validated against experimental values. By simulating the broadband metamorphic structure, we demonstrated that its light emission can cover the whole 1.0 - 1.7 μm range with a bandwidth of 550 nm at 10K. The emission spectrum was then assessed under realistic electrical injection conditions, at room temperature, through device-level simulations based on a coupled drift-diffusion and QD dynamics model. As metamorphic QD devices have been already fabricated with satisfying performances we believe that this proposal is a viable option to realize broader band light-emitting devices such as superluminescent diodes