arXiv subjects

M. Cestelli Guidi

Publications and source records attributed to M. Cestelli Guidi.

7 recordsLinked to original sources

arXiv2020

Tunable electronic structure and stoichiometry dependent disorder in Nanostructured VO$_x$ films

We present and discuss an original method to synthesize disordered Nanostructured (NS) VO$_x$ films with controlled stoichiometry and tunable electronic structures. In these NS films, the original lattice symmetry of the bulk vanadium oxides is broken and atoms are arranged in a highly disordered structure . The stoichiometry-dependent disorder as a function of the oxygen concentration has been characterized by in-situ X-ray Absorption Near-Edge Structure (XANES) spectroscopy identifying the spectroscopic fingerprints. Results show structural rearrangements that deviate from the octahedral symmetry with different coexisting disordered phases. The modulation of the electronic structure of the NS films based on the resulted stoichiometry and the quantum confinement in the NS particles are also discussed. We demonstrate the possibility to modulate the electronic structure of VO$_x$ NS films accessing new disordered atomic configurations with a controlled stoichiometry that provides an extraordinary opportunity to match a wide number of technological applications.

cond-mat.mes-hall↗

arXiv2019

Tunable vortex dynamics in proximity junction arrays: a possible accurate and sensitive 2D THz detector

An array of superconducting proximity islands has been shown to be highly tunable by electric and magnetic fields. Indeed, a small change in the electric and magnetic field can tune the system from a vortex Mott insulator to a vortex metal. This transition from localized to a non-localized state can occur as soon as the density of the superconducting vortices matches the density of the pinning sites in a non defective structure. The possibility of further modulation of non-localized superconducting states via enhancement of the superconducting order parameter or modulation of the Josephson plasma frequency is discussed. Based on the non-bolometric effects associated with the occurrence of non-equilibrium phenomena in this original superconducting networks we discuss also the possible applications of this array for a conceptually new type of radiation detector.

cond-mat.supr-con↗

arXiv2010

Fast IR Array Detector for Transverse Beam Diagnostics at DAΦNE

At the Laboratori Nazionali di Frascati of the National Institute of Nuclear Physics (INFN) an infrared (IR) array detector with fast response time has been built and assembled in order to collect the IR image of e-/e+ sources of the DAΦNE collider. Such detector is made by 32 bilinear pixels with an individual size of 50x50 μm2 and a response time of ~1 ns. In the framework of an experiment funded by the INFN Vth Committee dedicated to beam diagnostics, the device with its electronic board has been tested and installed on the DAΦNE positron ring. A preliminary characterization of few pixels of the array and of the electronics has been carried out at the IR beamline SINBAD at DAΦNE. In particular the detection of the IR source of the e- beam has been observed using four pixels of the array acquiring signals simultaneously with a four channels scope at 1 GHz and at 10 Gsamples/s. The acquisition of four pixels allowed monitoring in real time differences in the bunch signals in the vertical direction. A preliminary analysis of data is presented and discussed. In particular we will outline the correlation between signals and displacements of the source occurring with bunch refilling during a complete shift of DAΦNE.

physics.acc-ph↗

arXiv2008

Observation of charge-density-wave excitations in manganites

In the optical conductivity of four different manganites with commensurate charge order (CO), strong peaks appear in the meV range below the ordering temperature T_{CO}. They are similar to those reported for one-dimensional charge density waves (CDW) and are assigned to pinned phasons. The peaks and their overtones allow one to obtain, for La{1-n/8}Ca{n/8}$MnO{3} with n = 5, 6, the electron-phonon coupling, the effective mass of the CO system, and its contribution to the dielectric constant. These results support a description of the CO in La-Ca manganites in terms of moderately weak-coupling and of the CDW theory.

cond-mat.str-el↗

arXiv2007

Effect of Mn substitution by Ga on the optical properties of a metallic manganite

In a metallic manganite like La(2/3)Sr(1/3)MnO(3), the substitution of Mn(+3) by Ga(+3) dilutes the ferromagnetic order and locally cancels the Jahn-Teller distortion, without heavily affecting the crystal structure. One can thus follow the changes in the charge dynamics induced by Ga, until the ferro-metallic manganite is turned into an insulator. Here this phenomenon is studied in detail through the infrared reflectivity of five samples of La(2/3)Sr(1/3)Mn(1-x)Ga(x)O(3), with x increasing from 0 to 0.30 and for 50 < T < 320 K. A simple model which links the measured optical parameters to the magnetization M(x, T) well describes the behavior of the plasma frequency, the scattering rate, and the mid-infrared absorption along the metal-to-insulator transition.

cond-mat.str-el↗

arXiv2001

Evidence of ultra-slow polaron dynamics in low-doped manganites from 139La NMR-NQR and muon spin rotation

We report a 139La NMR investigation of low-doped insulating manganite samples (LaMnO(3+y) and La(1-x)Ca(x)MnO(3+y)) as a function of temperature. A volume fraction with fast nuclear relaxations was revealed by the inhomogeneous loss of the NMR signal over a broad temperature interval. Comparison with muSR data demonstrates that the wipe out of the 139La signal is mainly due to slowly fluctuating electric field gradients. This provides strong evidence for the slow diffusion of lattice excitations, identified with Jahn-Teller small polarons.

cond-mat.str-el↗

arXiv2001

Staggered magnetization, critical behavior and weak ferromagnetic propert ies of LaMnO$_3$ by muon spin rotation

We present a study of a microtwinned single crystal of LaMnO$_3$ by means of implanted muons. Two muon stopping sites are identified from the symmetry of the internal field in the ordered phase. The temperature dependence of these fields yields the behavior of the staggered magnetization from which a static critical exponent ($β=0.36(2)$) is extracted and discussed. The muon spin-spin relaxation rate shows a critical slowing down (contrary to preliminary findings) with a critical exponent $n=0.7(1)$, witnessing the Ising nature of the dynamic fluctuations. The muon precession frequencies vs. applied magnetic field reveal the saturation of the weak ferromagnetic domain structure originated by the Dzialoshinski-Moriya antisymmetric exchange.

cond-mat↗