Localization Transition in Multilayered Disordered Systems

The Anderson delocalization-localization transition is studied in multilayered systems with randomly placed interlayer bonds of density $p$ and strength $t$. In the absence of diagonal disorder (W=0), following an appropriate perturbation expansion, we estimate the mean free paths in the main directions and verify by scaling of the conductance that the states remain extended for any finite $p$, despite the interlayer disorder. In the presence of additional diagonal disorder ($W > 0$) we obtain an Anderson transition with critical disorder $W_c$ and localization length exponent $\nu$ independently of the direction. The critical conductance distribution $P_{c}(g)$ varies, however, for the parallel and the perpendicular directions. The results are discussed in connection to disordered anisotropic materials.Comment: 10 pages, Revtex file, 8 postscript files, minor change

Zero-bias anomaly in two-dimensional electron layers and multiwall nanotubes

The zero-bias anomaly in the dependence of the tunneling density of states $\nu (\epsilon)$ on the energy $\epsilon$ of the tunneling particle for two- and one-dimensional multilayered structures is studied. We show that for a ballistic two-dimensional (2D) system the first order interaction correction to DOS due to the plasmon excitations studied by Khveshchenko and Reizer is partly compensated by the contribution of electron-hole pairs which is twice as small and has the opposite sign. For multilayered systems the total correction to the density of states near the Fermi energy has the form $\delta \nu/\nu_0 = {max} (| \epsilon |, \epsilon^*)/4\epsilon_F$, where $\epsilon^*$ is the plasmon energy gap of the multilayered 2D system. In the case of one-dimensional conductors we study multiwall nanotubes with the elastic mean free path exceeding the radius of the nanotube. The dependence of the tunneling density of states energy, temperature and on the number of shells is found.Comment: 8 pages, 3 figure

Bound Chains of Tilted Dipoles in Layered Systems

Ultracold polar molecules in multilayered systems have been experimentally realized very recently. While experiments study these systems almost exclusively through their chemical reactivity, the outlook for creating and manipulating exotic few- and many-body physics in dipolar systems is fascinating. Here we concentrate on few-body states in a multilayered setup. We exploit the geometry of the interlayer potential to calculate the two- and three-body chains with one molecule in each layer. The focus is on dipoles that are aligned at some angle with respect to the layer planes by means of an external eletric field. The binding energy and the spatial structure of the bound states are studied in several different ways using analytical approaches. The results are compared to stochastic variational calculations and very good agreement is found. We conclude that approximations based on harmonic oscillator potentials are accurate even for tilted dipoles when the geometry of the potential landscape is taken into account.Comment: 10 pages, 6 figures. Submitted to Few-body Systems special issue on Critical Stability, revised versio

Electrical signature of individual magnetic skyrmions in multilayered systems

Magnetic skyrmions are topologically protected whirling spin textures that can be stabilized in magnetic materials in which a chiral interaction is present. Their limited size together with their robustness against the external perturbations promote them as the ultimate magnetic storage bit in a novel generation of memory and logic devices. Despite many examples of the signature of magnetic skyrmions in the electrical signal, only low temperature measurements, mainly in magnetic materials with B20 crystal structure, have demonstrated the skyrmions contribution to the electrical transport properties. Using the combination of Magnetic Force Microscopy (MFM) and Hall resistivity measurements, we demonstrate the electrical detection of sub-100 nm skyrmions in multilayered thin film at room temperature (RT). We furthermore analyse the room temperature Hall signal of a single skyrmion which contribution is mainly dominated by anomalous Hall effect.Comment: 13 pages, 4 figure

Solid-state interdiffusion reactions in Ni/Ti and Ni/Zr multilayered thin films

We have performed a comparative transmission electron microscopy study of solid-state interdiffusion reactions in multilayered Ni/Zr and Ni/Ti thin films. The Ni-Zr reaction product was amorphous while the Ni-Ti reaction product was a simple intermetallic compound. Because thermodynamic and chemical properties of these two alloy systems are similar, we suggest kinetic origins for this difference in reaction product

Observation of Resonant Diffusive Radiation in Random Multilayered Systems

Diffusive Radiation is a new type of radiation predicted to occur in randomly inhomogeneous media due to the multiple scattering of pseudophotons. This theoretical effect is now observed experimentally. The radiation is generated by the passage of electrons of energy 200KeV-2.2MeV through a random stack of films in the visible light region. The radiation intensity increases resonantly provided the Cherenkov condition is satisfied for the average dielectric constant of the medium. The observed angular dependence and electron resonance energy are in agreement with the theoretical predictions. These observations open a road to application of diffusive radiation in particle detection, astrophysics, soft X-ray generation and etc.. `Comment: 4pages, 4figure

LibCPIXE: a PIXE simulation open-source library for multilayered samples

Most particle induced X-ray emission (PIXE) data analysis codes are not focused on handling multilayered samples. We have developed an open-source library called "LibCPIXE", for PIXE data analysis. It is written in standard C and implements functions for simulating X-ray yields of PIXE spectra taken from arbitrary samples, including multilayered targets. The library is designed to be fast, portable, modular and scalable, as well as to facilitate its incorporation into any existing program. In order to demonstrate the capabilities of the library, a program called CPIXE was developed and used to analyze various real samples involving both bulk and layered samples. Just as the library, the CPIXE source code is freely available under the General Public License. We demonstrate that it runs both under GNU/Linux systems as well as under MS Windows. There is in principle no limitation to port it to other platforms

A multilayered effective medium model for the roughness effect on the Casimir force

A multilayered effective medium model is proposed to calculate the contribution of surface roughness to the Casimir force. In this model the rough layer has its optical properties derived from an effective medium approximation, with the rough layer considered as the mixing of voids and solid material. The rough layer can be divided into sublayers consisting of different volume fractions of voids and solid material as a function of the roughness surface profile. The Casimir force is then calculated using the generalizations of the Lifshitz theory for multilayered planar systems. Predictions of the Casimir force based on the proposed model are compared with those of well known methods of calculation, usually restricted to be used with large scale roughness. It is concluded that the effect of short scale roughness as predicted by this model is considerably larger than what could be expected from the extrapolation of the results obtained by the other methods

Resonant Diffusive Radiation in Random Multilayered Systems

We have theoretically shown that the yield of diffuse radiation generated by relativistic electrons passing random multilayered systems can be increased when a resonant condition is met. Resonant condition can be satisfied for the wavelength region representing visible light as well as soft X-rays. The intensity of diffusive soft X-rays for specific multilayered systems consisting of two components is compared with the intensity of Cherenkov radiation. For radiation at photon energy of $99.4eV$, the intensity of Resonant Diffusive Radiation (RDR) generated by $5MeV$ electrons passing a $Be/Si$ multilayer exceeds the intensity of Cherenkov radiation by a factor of $\approx 60$ for electrons with the same energy passing a $Si$ foil. For a photon energy of $453eV$ and $13MeV$ electrons passing $Be/Ti$ multilayer generate RDR exceeding Cherenkov radiation generated by electrons passing a $Ti$ foils by a factor $\approx 130$.Comment: Talk presented at the RC2005, Frascati, Ital