arXiv subjects

L. Martini

Publications and source records attributed to L. Martini.

4 recordsLinked to original sources

arXiv2022

Two-color polarization control on angularly resolved attosecond time delays

Measured photoionization time delays may exhibit large variations as a function of the emission angles, even for spherically symmetric targets, as shown in recent RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) experiments. The contributions from different pathways to the two-photon quantum channels can already explain the observed phase jumps that shape those angular distributions. Here, we propose a simple analytical model to describe angularly-resolved RABBITT spectra as a function of the relative polarization angle between the ionizing attosecond pulse train and the assisting IR field. We demonstrate that the angular dependencies of the measured delays can be analytically predicted and the position of the phase jumps reduced to the analysis of a few relevant parameters.

physics.atom-ph↗

arXiv2022

Analytical model for attosecond time delays and Fano's propensity rules in the continuum

Extracting single photoionization time delays associated with atomic (or molecular) species from attosecond time scale two-photon experiments usually relies on the theoretical description of continuum-continuum transitions. The available models for those processes predict a universal phase contribution, independent of the angular quantum numbers of final states. However, a recent experimental-theoretical study [Fuchs, \emph{et al.} Optica 7, 154 (2020)] determined a sizable time delay dependence on the angular momentum of near-threshold photoelectrons. In this study, we present an analytical model for the two-photon two-color transition matrix amplitudes that reproduces the phase dependence on the angular quantum number of final states. Finally, we show that our analytical model can also describe the generalized Fano's propensity rules [Busto, \emph{et al.} Phys. Rev. Lett. 123, 133201 (2019)] for laser-assisted photoionization.

physics.atom-ph↗

arXiv2019

Going beyond copper: wafer-scale synthesis of graphene on sapphire

The adoption of graphene in electronics, optoelectronics and photonics is hindered by the difficulty in obtaining high quality material on technologically-relevant substrates, over wafer-scale sizes and with metal contamination levels compatible with industrial requirements. To date, the direct growth of graphene on insulating substrates has proved to be challenging, usually requiring metal-catalysts or yielding defective graphene. In this work, we demonstrate a metal-free approach implemented in commercially available reactors to obtain high-quality monolayer graphene on c-plane sapphire substrates via chemical vapour deposition (CVD). We identify via low energy electron diffraction (LEED), low energy electron microscopy (LEEM) and scanning tunneling microscopy (STM) measurements the Al-rich reconstruction root31R9 of sapphire to be crucial for obtaining epitaxial graphene. Raman spectroscopy and electrical transport measurements reveal high-quality graphene with mobilities consistently above 2000 cm2/Vs. We scale up the process to 4-inch and 6-inch wafer sizes and demonstrate that metal contamination levels are within the limits for back-end-of-line (BEOL) integration. The growth process introduced here establishes a method for the synthesis of wafer-scale graphene films on a technologically viable basis.

physics.app-ph↗

arXiv2002

Superconducting Properties of Highly Dense MgB2 Bulk Materials

Highly dense MgB2 policrystalline bulk materials, obtained by reactive liquid infiltration, have been characterized in their superconducting transport and magnetic properties in magnetic field and in a temperature range of interest for the MgB2 compound. The products have a granular morphology of composite nature and their overall density affects their properties. The irreversibility line, Bc1(T) values, magnetically measured current densities and the trapped magnetic field are evaluated by susceptibility curves and hysteresis curves, both obtained by SQUID magnetometry for samples of different density, up to 35K and up to 5T applied magnetic field. The experimental results have been compared with the best values reported in the literature for other bulk sintering techniques.

cond-mat.supr-con↗