A. Sacchetti

OHB (Germany)

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P. Postorino

Sapienza University of Rome

M. Lavagnini

ETH Zurich

I. R. Fisher

Stanford University

L. Degiorgi

ETH Zurich

P. Dore

Sapienza University of Rome

D. Di Castro

University of Rome Tor Vergata

Maria Baldini

Fermi National Accelerator Laboratory

A. Nucara

Sapienza University of Rome

N. Ru

Stanford University

E. Arcangeletti

Sapienza University of Rome

Cooperative Institutions

Sapienza University of Rome

European Space Research and Technology Centre

ETH Zurich

Centre National de la Recherche Scientifique

Istituto Nazionale per la Fisica della Materia

Osservatorio Astrofisico di Catania

Istituto Nazionale di Fisica Nucleare

National Institute for Astrophysics

National Research Council

Politecnico di Milano

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Raman spectra of neutron-irradiated and Al-dopedMgB2

Physical Review B (2006)

D. Di Castro E. Cappelluti M. Lavagnini A. Sacchetti A. Palenzona

We carried out Raman measurements on neutron-irradiated and Al-doped ${\mathrm{MgB}}_{2}$ samples. The Raman spectrum changes substantially in both cases and in a similar way, with the appearance of high-frequency spectral structures, whose spectral weight increases with increasing Al concentration and neutron irradiation fluence. In particular, in Al-doped samples the high-frequency peaks slightly harden with increasing Al concentration, due to the lattice compression, whereas in the neutron-irradiated samples, where no atomic substitution occurs, no frequency shift is detected. The appearance of high-frequency spectral structures in the irradiated samples, similar to those observed in Al-doped ones, is quite unexpected. By direct comparison of the Raman spectra with literature experimental phonon densities of states, we show that the modifications of the Raman spectrum in both irradiated and Al-doped samples are due to disorder-induced violations of the Raman selection rules. Theoretical calculations of the phonon density of states support this hypothesis, and demonstrate that the high-frequency structures arise mostly from contributions at $\mathbf{q}\ensuremath{\ne}\mathbf{0}$ of the ${E}_{2g}$ phonon mode.

Neutron irradiation

10.1103/physrevb.74.100505

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Citations (36)

MicroRaman spectroscopy on LiMn2O4: warnings on laser-induced thermal decomposition

Solid State Ionics (2004)

A. Paolone A. Sacchetti T. Corridoni P. Postorino R. Cantelli

10.1016/j.ssi.2004.02.002

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Citations (45)

Pressure-induced quenching of the charge-density-wave state in rare-earth tritellurides observed by x-ray diffraction

Physical Review B (2009)

A. Sacchetti Cathie L. Condron S. N. Gvasaliya F. Pfuner M. Lavagnini

We report an x-ray diffraction study on the charge-density-wave (CDW) LaTe$_3$ and CeTe$_3$ compounds as a function of pressure. We extract the lattice constants and the CDW modulation wave-vector, and provide direct evidence for a pressure-induced quenching of the CDW phase. We observe subtle differences between the chemical and mechanical compression of the lattice. We account for these with a scenario where the effective dimensionality in these CDW systems is dependent on the type of lattice compression and has a direct impact on the degree of Fermi surface nesting and on the strength of fluctuation effects.

Charge Density Wave

Lattice constant

Lattice (music)

Charge density

Wave vector

10.1103/physrevb.79.201101

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Citations (35)

Temperature dependence of the optical phonons inSrMnO3manganite: Evidence of a low-temperature structural transition in the hexagonal compound

Physical Review B (2005)

A. Sacchetti Maria Baldini F. Crispoldi P. Postorino P. Dore

Infrared and Raman spectroscopies were employed to study the temperature dependence of the optical phonons of the $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3}$ manganite in both the hexagonal and the cubic phase. Changes in the phonon spectrum of the hexagonal $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3}$ (four-layer structure) observed on decreasing temperature indicate that a subtle structural transition occurs in the system between 200 and $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We propose that the transition consists in a change from the four-layer to a six-layer structure, in which the high-temperature crystal symmetry is retained.

Manganite

10.1103/physrevb.72.172407

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Citations (23)

The planetary transit and oscillations (PLATO) mission status: flight model build and initial ground testing

Space Telescopes and Instrumentation 2020: Optical, Infrared, and Millimeter Wave (2024)

José Lorenzo Alvarez T. Walloschek A. M. Heras José Aroca Tobias Boenke

PLATO (PLAnetary Transits and Oscillations) mission is a space-based optical multi-camera photometer mission of the European Space Agency (ESA) to identify and characterize exoplanets and their hosting stars using two main techniques: planetary transit and asteroseismology. Selected as the M3 (third Medium class mission) of the ESA 2015-2025 Cosmic Vision program, PLATO is scheduled to launch end of 2026 and designed for 4 years of nominal observation. The PLATO spacecraft is composed of a Service Module and a Payload Module. The Service Module comprises all the conventional spacecraft subsystems and the sun shield with attached solar arrays. The Payload Module consists of a highly stable optical bench, equipped with 26 optical cameras covering a global field of view of > 2232deg². The PLATO spacecraft data is complemented by ground-based observations and processed by a dedicated Science Ground Segment. We describe the mission and spacecraft architecture and provide a view of the current status of development.

10.1117/12.3020491

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Competitive effects on the high‐pressure phase diagram of manganites

physica status solidi (b) (2004)

P. Postorino A. Sacchetti Massimo Capone P. Dore

Abstract Recent infrared absorption measurements performed at different pressures and temperatures on the La 0.75 Ca 0.25 MnO 3 manganite provided the insulator‐to‐metal transition temperature T IM ( P ), i.e. the P–T phase diagram of the manganite. We report an extended data analysis, by considering in detail pressure and temperature dependence of the observed IR active phonon and of the absorption spectral weights N *. The phonon pressure‐dependence, consistently with the P–T phase diagram, indicates the onset of a new localizing interaction above P * = 6–7 GPa. Finally a simple theoretical model will be employed to give a qualitative explanation of the observed high‐pressure behavior and to suggest the relevance of the charge‐localizing super‐exchange magnetic interaction in the very high‐pressure regime. Within this framework the asymptotic regime at high pressure is ascribed to the competition between the magnetic super‐ and double‐exchange interactions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Manganite

Charge ordering

10.1002/pssb.200405205

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Citations (9)

Evidence for coupling between charge density waves and phonons in two-dimensional rare-earth tritellurides

Physical Review B (2008)

M. Lavagnini Maria Baldini A. Sacchetti D. Di Castro B. Delley

We report on a Raman scattering investigation of the charge-density-wave (CDW), quasi two-dimensional rare-earth tri-tellurides $R$Te$_3$ ($R$= La, Ce, Pr, Nd, Sm, Gd and Dy) at ambient pressure, and of LaTe$_3$ and CeTe$_3$ under externally applied pressure. The observed phonon peaks can be ascribed to the Raman active modes for both the undistorted as well as the distorted lattice in the CDW state by means of a first principles calculation. The latter also predicts the Kohn anomaly in the phonon dispersion, driving the CDW transition. The integrated intensity of the two most prominent modes scales as a characteristic power of the CDW-gap amplitude upon compressing the lattice, which provides clear evidence for the tight coupling between the CDW condensate and the vibrational modes.

Charge Density Wave

Lattice (music)

Charge density

10.1103/physrevb.78.201101

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Citations (52)

CCDC 734071: Experimental Crystal Structure Determination

The Cambridge Structural Database (2010)

Giordano Lesma Nicola Landoni T. Pilati A. Sacchetti Alessandra Silvani

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

10.5517/ccsmvqy

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Pressure Tuning of Electron-Phonon Coupling: The Insulator to Metal Transition in Manganites

Physical Review Letters (2003)

P. Postorino A. Congeduti P. Dore A. Sacchetti Federico A. Gorelli

An extended temperature and pressure-dependent investigation is carried out on a La0.75Ca0.25MnO3 sample exploiting the infrared absorption technique coupled to a diamond anvil cell. The pressure dependence of the insulator to metal transition temperature T(IM) is determined for the first time up to 11.2 GPa. The T(IM)(P) curve we propose to model the present data has an exponential-like behavior with an associated characteristic pressure P* playing the role of a decay constant. It is found that the equivalence between an external and an internal (chemical) pressure holds over a limited range of pressure, namely, P< or =2P*. Moreover, a certain universality character is associated with the proposed model curve in its ability to account for a large class of low-disorder manganites characterized by intermediate electron-phonon coupling.

Metal–insulator transition

Coupling constant

10.1103/physrevlett.91.175501

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Citations (76)

Stark effect on (H2+)-like molecules

V. Grecchi Hynek Kovařík André Martínez A. Sacchetti Vania Sordoni

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