arXiv subjects

Fabrizio Carbone

Publications and source records attributed to Fabrizio Carbone.

43 records · Page 3Linked to original sources

arXiv2016

A Versatile Setup for Ultrafast Broadband Optical Spectroscopy of Coherent Collective Modes in Strongly Correlated Quantum Systems

A femtosecond pump-probe setup is described that is optimised for broadband transient reflectivity experiments on solid samples over a wide range of temperatures. By combining a temporal resolution of 45 fs and a broad detection range between 1.75 and 2.85 eV, this apparatus can provide insightful information on the interplay between coherent collective modes and high-energy electronic excitations, which is one of the distinctive characteristics of strongly interacting and correlated quantum systems. The use of a single-shot readout CMOS array detector at frame rates up to 10 kHz allows to resolve coherent oscillations with amplitudes below 10$^{-4}$ in $Δ$R/R. We demonstrate the operation of this setup on the prototypical charge-transfer insulator La$_2$CuO$_4$, revealing the presence of coherent optical phonons with frequencies as high as 13 THz.

physics.ins-det↗

arXiv2016

Shaping, imaging and controlling plasmonic interference fields at buried interfaces

Filming and controlling plasmons at buried interfaces with nanometer (nm) and femtosecond (fs) resolution has yet to be achieved and is critical for next generation plasmonic/electronic devices. In this work, we use light to excite and shape a plasmonic interference pattern at a buried metal-dielectric interface in a nanostructured thin film. Plasmons are launched from a photoexcited array of nanocavities and their propagation is filmed via photon-induced near-field electron microscopy (PINEM). The resulting movie directly captures the plasmon dynamics, allowing quantification of their group velocity at approximately 0.3c, consistent with our theoretical predictions. Furthermore, we show that the light polarization and nanocavity design can be tailored to shape transient plasmonic gratings at the nanoscale. These results, demonstrating dynamical imaging with PINEM, pave the way for the fs/nm visualization and control of plasmonic fields in advanced heterostructures based on novel 2D materials such as graphene, MoS$_2$, and ultrathin metal films.

cond-mat.mes-hall↗

arXiv2016

Electron Diffraction by Plasmon Waves

An electron beam traversing a structured plasmonic field is shown to undergo diffraction with characteristic angular patterns of both elastic and inelastic outgoing electron components. In particular, a plasmonic {\it grating} (e.g., a standing wave formed by two counter-propagating plasmons in a thin film) produces diffraction orders of the same parity as the net number of exchanged plasmons. Large diffracted beam fractions are predicted to occur for realistic plasmon intensities in attainable geometries due to a combination of phase and amplitude changes locally imprinted on the passing electron wave. Our study opens new vistas in the study of multiphoton exchanges between electron beams and evanescent optical fields with unexplored effects related to the transversal component of the electron wave function.

cond-mat.mes-hall↗

arXiv2016

Order/disorder dynamics in a dodecanethiol-capped gold nanoparticles supracrystal by small-angle ultrafast electron diffraction

In metal nanoparticles (NPs) supracrystals, the metallic core provides some key properties, e.g. magnetization, plasmonic response or conductivity, with the ligand molecules giving rise to others like solubility, assembly or interaction with biomolecules. The formation of these supracrystals depends on a complex interplay between many forces, some stemming from the core, some from the ligands. At present, there is no known approach to characterize the local order of ligand molecules or their dynamics with atomic spatial resolution. Here, we develop a methodology based on small-angle ultrafast electron diffraction combined with angular cross-correlation analysis to characterize a two-dimensional supracrystal of dodecanethiol-coated gold NPs. We retrieve the static arrangement of the ligands, showing that at equilibrium they order in a preferential orientation on the NPs surface and throughout the two-dimensional supracrystal. Upon light excitation, positional disorder is induced in the supracrystal, while its overall homogeneity is surprisingly found to transiently increase. This suggests that transient annealing of the supracrystal takes place within few picoseconds (ps). This methodology will enable the systematic investigation of the dynamical structural properties of nano-assembled materials containing light elements, relevant for biological applications.

cond-mat.mtrl-sci↗

arXiv2015

The role of the coherence in the cross-correlation analysis of diffraction patterns from two-dimensional dense mono-disperse systems

The investigation of the static and dynamic structural properties of colloidal systems relies on techniques capable of atomic resolution in real space and femtosecond resolution in time. Recently, the cross-correlation function (CCF) analysis of both X-rays and electron diffraction patterns from dilute and dense aggregates has demonstrated the ability to retrieve information on the sample's local order and symmetry. Open questions remain regarding the role of the beam coherence in the formation of the diffraction pattern and the properties of the CCF, especially in dense systems. Here, we simulate the diffraction patterns of dense two-dimensional monodisperse systems of different symmetries, varying the transverse coherence of the probing wave, and analyze their CCF. We study samples with different symmetries at different size scale, as for example, pentamers arranged into a four-fold lattice where each pentamer is surrounded by triangular lattices, both ordered and disordered. In such systems, different symmetry modulations are arising in the CCF at specific scattering vectors. We demonstrate that the amplitude of the CCF is a fingerprint of the degree of the ordering in the sample and that at partial transverse coherence, the CCF of a dense sample corresponds to that of an individual scattering object.

cond-mat.other↗

arXiv2015

Probing the electron-phonon interaction in correlated systems with coherent lattice fluctuation spectroscopy

Tailoring the properties of correlated oxides is accomplished by chemical doping, pressure, temperature or magnetic field. Photoexcitation is a valid alternative to reach out-of-equilibrium states otherwise inaccessible. Here, we quantitatively estimate the coupling between a lattice distortion and the charge-transfer excitation in (La$_2$CuO$_{4+δ}$). We photoinduce a coherent La ion vibration and monitor the response of the optical constants in a broad energy range, providing quantitative information on the electron-phonon matrix element that can be compared to theoretical models. We propose the same methodology to probe electron-electron interactions in other materials.

cond-mat.supr-con↗

arXiv2009

Evidence for strongly coupled charge-density-wave ordering in three-dimensional RE5Ir4Si10 compounds by optical measurements

We report optical spectra of Lu$_5$Ir$_4$Si$_{10}$ and Er$_5$Ir$_4$Si$_{10}$, exhibiting the phenomenon of coexisting superconductivity or antiferromagnetism and charge density wave (CDW) order. We measure the maximum value of the charge density wave gap present on part of the Fermi surface of Lu5Ir4Si10, corresponding to a ratio 2Δ/k_B T_CDW \approx 10, well above the value in the limit of weak electron-phonon coupling. Strong electron-phonon coupling was confirmed by analyzing the optical conductivity with the Holstein model describing the electron-phonon interactions, indicating the coupling to phonons centered at 30 meV, with a coupling constant λ\approx 2.6. Finally we provide evidence that approximately 16 % of the Fermi surface of Lu5Ir4Si10 becomes gapped in the CDW state.

cond-mat.str-el↗