arXiv subjects

L. Martinelli

Publications and source records attributed to L. Martinelli.

25 records · Page 2Linked to original sources

arXiv2021

Charge and spin order dichotomy in NdNiO$_2$ driven by SrTiO$_3$ capping layer

Superconductivity in infinite-layer nickelates holds exciting analogies with that of cuprates, with similar structures and $3d$-electron count. Using resonant inelastic x-ray scattering (RIXS) we studied electronic and magnetic excitations and charge density correlations in Nd$_{1-x}$Sr$_{x}$NiO$_2$ thin films with and without an SrTiO$_3$ capping layer. We observe dispersing magnons only in the capped samples, progressively dampened at higher doping. In addition, we detect an elastic resonant scattering peak in the uncapped $x=0$ compound at wave vector (1/3,0), remindful of the charge order signal in hole doped cuprates. The peak weakens at $x=0.05$ and disappears in the superconducting $x=0.20$ film. The uncapped samples also present a higher degree of Ni$3d$-Nd$5d$ hybridization and a smaller anisotropy of the Ni$3d$ occupation with respect to the capped samples. The role of the capping on the possible hydrogen incorporation or on other mechanisms responsible for the electronic reconstruction far from the interface remains to be understood.

cond-mat.supr-con↗

arXiv2019

Spin- and angle-resolved photoemission studies of the electronic structure of Si(110)"16x2" surfaces

The electronic structure of Si(110)"16 x 2" double-domain, single-domain and 1 x 1 surfaces have been investigated using spin- and angle-resolved photoemission at sample temperatures of 77 K and 300 K. Angle-resolved photoemission was conducted using horizontally- and vertically-polarised 60 eV and 80 eV photons. Band-dispersion maps revealed four surface states ($S_1$ to $S_4$) which were assigned to silicon dangling bonds on the basis of measured binding energies and photoemission intensity changes between horizontal and vertical light polarisations. Three surface states ($S_1$, $S_2$ and $S_4$), observed in the Si(110)"16 x 2" reconstruction, were assigned to Si adatoms and Si atoms present at the edges of the corrugated terrace structure. Only one of the four surface states, $S_3$, was observed in both the Si(110)"16 x 2" and 1 x 1 band maps and consequently attributed to the pervasive Si zigzag chains that are components of both the Si(110)"16 x 2" and 1 x 1 surfaces. A state in the bulk-band region was attributed to an in-plane bond. All data were consistent with the adatom-buckling model of the Si(110)"16 x 2" surface. Whilst room temperature measurements of $P_y$ and $P_z$ were statistically compatible with zero, $P_x$ measurements of the enantiomorphic A-type and B-type Si(110)"16 x 2" surfaces gave small average polarisations of around 1.5\% that were opposite in sign. Further measurements at 77 K on A-type Si(110)"16 x 2" surface gave a smaller value of +0.3\%. An upper limit of $\sim1\%$ may thus be taken for the longitudinal polarisation.

cond-mat.mtrl-sci↗

arXiv2019

Mechanical stress dependence of the Fermi level pinning on an oxidized silicon surface

A combination of micro-Raman spectroscopy and micro-XPS (X-ray photo-electron spectroscopy) mapping on statically deflected p-type silicon cantilevers is used to study the mechanical stress dependence of the Fermi level pinning at an oxidized silicon (001) surface. With uniaxial compressive and tensile stress applied parallel to the $\langle$110$\rangle$ crystal direction, the observations are relevant to the electronic properties of strain-silicon nano-devices with large surface-to-volume ratios such as nanowires and nanomembranes. The surface Fermi level pinning is found to be even in applied stress, a fact that may be related to the symmetry of the Pb$_0$ silicon/oxide interface defects. For stresses up to 160 MPa, an increase in the pinning energy of 0.16 meV/MPa is observed for compressive stress, while for tensile stress it increases by 0.11 meV/MPa. Using the bulk, valence band deformation potentials the reduction in surface band bending in compression (0.09 meV/MPa) and in tension (0.13 meV/MPa) can be estimated.

cond-mat.mes-hall↗

arXiv2018

Construction techniques and performances of a full-size prototype Micromegas chamber for the ATLAS muon spectrometer upgrade

A full-size prototype of a Micromegas precision tracking chamber for the upgrade of the ATLAS detector at the LHC Collider has been built between October 2015 and April 2016. This paper describes in detail the procedures used in constructing the single modules of the chamber in various INFN laboratories and the final assembly at the Laboratori Nazionali di Frascati (LNF). Results of the chamber exposure to the CERN SPS/H8 beam line in June 2016 are also presented. The performances achieved in the construction and the results of the test beam are compared with the requirements, which are imposed by the severe environment during the data-taking of the LHC foreseen for the next years.

physics.ins-det↗

arXiv2018

Evidence of nanoscale Anderson localization induced by intrinsic compositional disorder in InGaN/GaN quantum wells by scanning tunneling luminescence spectroscopy

We present direct experimental evidences of Anderson localization induced by the intrinsic alloy compositional disorder of InGaN/GaN quantum wells. Our approach relies on the measurement of the luminescence spectrum under local injection of electrons from a scanning tunneling microscope tip into a near-surface single quantum well. Fluctuations in the emission line shape are observed on a few-nanometer scale. Narrow emission peaks characteristic of single localized states are resolved. Calculations in the framework of the localization landscape theory provide the effective confining potential map stemming from composition fluctuations. This theory explains well the observed nanometer scale carrier localization and the energies of these Anderson-type localized states. The energy spreading of the emission from localized states is consistent with the usually observed very broad photo- or electro-luminescence spectra of InGaN/GaN quantum well structures.

cond-mat.mes-hall↗

arXiv2018

Exciton diffusion in WSe2 monolayers embedded in a van der Waals heterostructure

We have combined spatially-resolved steady-state micro-photoluminescence ($μ$PL) with time-resolved photoluminescence (TRPL) to investigate the exciton diffusion in a WSe$_2$ monolayer encapsulated with hexagonal boron nitride (hBN). At 300 K, we extract an exciton diffusion length $L_X= 0.36\pm 0.02 \; μ$m and an exciton diffusion coefficient of $D_X=14.5 \pm 2\;\mbox{cm}^2$/s. This represents a nearly 10-fold increase in the effective mobility of excitons with respect to several previously reported values on nonencapsulated samples. At cryogenic temperatures, the high optical quality of these samples has allowed us to discriminate the diffusion of the different exciton species : bright and dark neutral excitons, as well as charged excitons. The longer lifetime of dark neutral excitons yields a larger diffusion length of $L_{X^D}=1.5\pm 0.02 \;μ$m.

cond-mat.mes-hall↗

arXiv2016

Luminescence imaging of photoelectron spin precession during drift in p-type GaAs

Using a microfabricated, p-type GaAs Hall bar, is it shown that the combined application of co-planar electric and magnetic fields enables the observation at 50 K of spatial oscillations of the photoluminescence circular polarization due to the precession of drifting spin-polarized photoelec- trons. Observation of these oscillations as a function of electric field E gives a direct measurement of the minority carrier drift mobility and reveals that, for E = 800 V/cm, spin coherence is preserved over a length as large as 25μm.

cond-mat.mes-hall↗