Search

Your search keyword '"Ortolani, M"' showing total 25 results
Start Over Author "Ortolani, M" Journal physical review b
25 results on '"Ortolani, M"'

1. Electron-phonon coupling in n -type Ge two-dimensional systems

Author

Ciano, C., primary, Persichetti, L., additional, Montanari, M., additional, Di Gaspare, L., additional, Capellini, G., additional, Baldassarre, L., additional, Ortolani, M., additional, Pashkin, A., additional, Helm, M., additional, Winnerl, S., additional, Virgilio, M., additional, and De Seta, M., additional

Published
2020
Full Text
View/download PDF

2. Raman scattering versus infrared conductivity : evidence for one-dimensional conduction in La(2-x)Sr(x)CuO(4)

Author

Venturini, Francesca, Zhang, Q. -M., Hackl, R., Lucarelli, A., Lupi, S., Ortolani, M., Calvani, P., Kikugawa, N., Fujita, T., Venturini, Francesca, Zhang, Q. -M., Hackl, R., Lucarelli, A., Lupi, S., Ortolani, M., Calvani, P., Kikugawa, N., and Fujita, T.

Abstract

Raman and infrared (IR) spectra of an underdoped La_1.90Sr_0.10CuO4 single crystal have been measured as a function of temperature. Both techniques provide unconventional low-energy spectra. The IR conductivity exhibits features peaked at finite frequencies which do not have a counterpart in the Raman response. Below approximately 100 K a transfer of both Raman and IR spectral weight towards lower energies is found and a new component in the Raman response builds up being characterized by a very long lifetime of electrons propagating along the Cu-O bonds.

Published
2018

9. Multiband conductivity and a multigap superconducting phase inV3Sifilms from optical measurements at terahertz frequencies

Author

Perucchi, A., primary, Nicoletti, D., additional, Ortolani, M., additional, Marini, C., additional, Sopracase, R., additional, Lupi, S., additional, Schade, U., additional, Putti, M., additional, Pallecchi, I., additional, Tarantini, C., additional, Ferretti, M., additional, Ferdeghini, C., additional, Monni, M., additional, Bernardini, F., additional, Massidda, S., additional, and Dore, P., additional

Published
2010
Full Text
View/download PDF

21. Hardening of the soft phonon in bulk SrTiO3 interfaced with LaAlO3 and SrRuO3.

Author

Nucara, A., Ortolani, M., Baldassarre, L., Mohamed, W. S., Schade, U., Aurino, P. P., Kalaboukhov, A., Winkler, D., Khare, A., Granozio, F. Miletto, and Calvani, P.

Subjects
*PHONONS, *STRONTIUM titanate, *LANTHANUM compounds
Abstract

The low-temperature softening of the TO1 phonon of SrTiO3 (STO), which determines its incipient ferroelectricity, is known to be partially hindered either in the bulk under strong electric fields, or in thin STO films. Here we show, by terahertz (THz) reflectivity measurements, that a similar effect is produced in bulk STO and at zero static field by ultrathin metallic films on its surface, like a 10-nm-thick film of SrRuO3 (SRO), or the two-dimensional electron system (2DES) present at the interface with LaAlO3. In SRO/STO, the observed hardening is well explained by the depolarizing action of the SRO free electrons which follow adiabatically the ion motion. In LAO/STO, a weaker TO1 hardening could be detected by patterning the 2DES in the form of microstripes and using a polarized THz field parallel (E‖) or orthogonal (E⊥) to the stripes. At 10 K, when TO1 is excited together with the free electrons by E‖, its absorbance is harder by about 7 cm-1 than that measured when TO1 is coupled to the plasmon-polariton confined within the stripes, being excited by E⊥. [ABSTRACT FROM AUTHOR]

Published
2016
Full Text
View/download PDF

22. Near- and far-infrared absorption and electronic structure of Ge-SiGe multiple quantum wells

Author

Paolo Calvani, Michele Nardone, Yan Busby, Giovanni Pizzi, Giuseppe Nicotra, Corrado Spinella, Michele Ortolani, Giovanni Capellini, Michele Virgilio, Giuseppe Grosso, Stefano Lupi, M. De Seta, Florestano Evangelisti, Busby, Y, De Seta, M, Capellini, Giovanni, Evangelisti, F, Ortolani, M, Virgilio, M, Grosso, G, Pizzi, G, Calvani, P, Lupi, S, Nardone, M, Nicotra, G, Spinella, C., Busby, Y., DE SETA, Monica, Capellini, G., Evangelisti, F., Ortolani, M., Virgilio, M., Grosso, G., Pizzi, G., Calvani, P., Lupi, S., Nardone, M., and Nicotra, G.

Subjects
STRAIN, Intersubband transitions, Materials science, ALLOYS, Terahertz radiation, Infrared spectroscopy, Quantum Well, Electronic structure, Molecular physics, GeSi, Condensed Matter::Materials Science, symbols.namesake, Far infrared, HETEROSTRUCTURES, Quantum well, Condensed matter physics, Condensed Matter::Other, Doping, Heterojunction, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, Condensed Matter Physics, Electronic, Optical and Magnetic Materials, CASCADE EMITTERS, symbols, Raman spectroscopy, INTERSUBBAND ELECTROLUMINESCENCE
Abstract

We report an extensive study of strained $\text{Ge}/{\text{Si}}_{0.2}{\text{Ge}}_{0.8}$ multiquantum wells grown by ultrahigh-vacuum chemical-vapor deposition. The microstructural properties of the samples were characterized by transmission electron microscopy and Raman spectroscopy. Their electronic properties have been investigated by means of infrared absorption measurements. Both interband and intersubband transitions were analyzed. Intersubband absorption energies were found in the 20--50 meV range, depending on the quantum well width. Interband and intersubband transition energies have been successfully described by means of both a $\mathbit{k}\ensuremath{\cdot}\mathbit{p}$ approach and a tight-binding model. In particular, we found a conduction-band offset between the L edges of 124 meV, well suited for the development of optoelectronic devices operating in the terahertz range. We also found that the energy difference between the ${\ensuremath{\Delta}}_{2}$ minima in the barrier and the L minima in the well is only $\ensuremath{\sim}40\text{ }\text{meV}$. This explains the observed ineffectiveness of the transfer doping in the strained heterostructures considered.

Published
2010

23. Physical mechanisms of intersubband-absorption linewidth broadening ins-Ge/SiGe quantum wells

Author

Luciana Di Gaspare, Monica De Seta, Michele Ortolani, Giovanni Capellini, D. Sabbagh, Michele Virgilio, Virgilio, M, Sabbagh, D, Ortolani, M, DI GASPARE, Luciana, Capellini, Giovanni, and De Seta, M.

Subjects
Ir absorption, Materials science, Condensed matter physics, quantum wells, infrared spectroscopy, semiconductors, Chemical vapor deposition, Condensed Matter Physics, scattering mechenisms, Electronic, Optical and Magnetic Materials, Laser linewidth, Atomic physics, Homogeneous broadening, Absorption (electromagnetic radiation), Quantum well, Ge quantum well, IR absorption
Abstract

We analyze the linewidth of intersubband absorption features observed in n-type s-Ge/Ge0.82Si0.18 multiquantum wells grown on Si(001) substrates. Supported by a thorough theoretical modeling, we discuss the role on the line broadening of electron scattering due to interface roughness, spatial distribution and density of ionized donors, phonons, alloy disorder, and extended defects. To this aim, the absorption spectra of a set of samples featuring different well widths and doping profiles are measured obtaining a very good agreement with the theoretical results. We demonstrate values of the half width at half maximum of the E0->E1 absorption peak as small as 2 meV. Our analysis suggests that the coherence time of electron wave functions in n-doped Ge/SiGe quantum wells is not yet limited by intrinsic scattering mechanisms up to room temperature, opening new perspectives for the quantum design of silicon-based light emitting devices.

Published
2014

24. Combined effect of electron and lattice temperatures on the long intersubband relaxation times of Ge/SixGe1−xquantum wells

Author

Manfred Helm, D. Sabbagh, Michele Ortolani, Giovanni Capellini, Stephan Winnerl, Michele Virgilio, Martin Teich, Monica De Seta, Virgilio, M, Ortolani, M, Teich, M, Winner, S, Helm, M, Sabbagh, D, Capellini, G, and DE SETA, Monica

Subjects
Physics, Electron density, Condensed matter physics, Phonon scattering, Relaxation (NMR), semiconductors, Electron, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, Condensed Matter Physics, time-resolved spectroscopy, Spectral line, Electronic, Optical and Magnetic Materials, quantum wells, Lattice (order), Order of magnitude, Quantum well
Abstract

In this paper, we have experimentally and numerically studied the nonradiative intersubband (ISB) relaxation in $n$-type Ge/SiGe quantum well (QW) systems. Relaxation times have been probed by means of pump-probe experiments. An energy balance model has been used to interpret the experimental differential transmission spectra and to assess the relevance in the nonradiative relaxation dynamics of both electron and lattice temperature as well as of the carrier density. The comparison between experimental data and theoretical simulation allowed us to calibrate the interaction parameters which describe the electron-optical phonon scattering in two-dimensional (2D) Ge systems. Characteristic relaxation times has been calculated and compared with those of GaAs QWs as a function of the 2D electron density, of the subband energy separation, and of the lattice and electronic temperature. We found that ISB relaxation times for the Ge/SiGe systems are generally shorter than that previously calculated when the electron distribution was neglected. Nonetheless, our main result is that the relaxation time in Ge/SiGe QW systems is longer than 10 ps, also for transition energies above the Ge optical phonon energy, up to 300 K. Furthermore, we obtained that the relaxation times are at least one order of magnitude longer than in GaAs-based systems.

Published
2014

25. Electronic bands and optical conductivity of the Dzyaloshinsky-Moriya multiferroic Ba2CuGe2O7.

Author

Corasaniti, M., Barone, P., Nucara, A., Ortolani, M., Baldassarre, L., Fittipaldi, R., Granata, V., Rocco, L., Vecchione, A., Mohamed, W. S., Lorenzana, J., and Calvani, P.

Subjects
*ELECTRONIC band structure, *BARIUM, *OPTICAL conductivity
Abstract

We have measured the reflectivity in the ab plane and along the c axis of a single crystal of the Dzyaloshinsky-Moriya multiferroic Ba2CuGe2O7, from 20 to 300 K and from 700 to 24 000 cm-1. The resulting optical conductivity σ(ω) has been compared with the results of calculations of its electronic band structure based on density functional theory (DFT). A broad midinfrared band, which in the ab plane strongly hardens for decreasing temperature, is consistent with d-d transitions of the Cu atom. A further electronic absorption, whose edge falls in the near infrared and has a strong O-p character, unusually softens with decreasing temperature by more than 0.15 eV, in both polarizations. Calculations show that the behavior with temperature of those electronic bands can be related to distortions of the CuO4 tetrahedra. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results