Biomedical subjects

P Calvani

Publications and source records attributed to P Calvani.

At least 19 recordsLinked to original sources

PubMed2006

Low-energy electrodynamics of superconducting diamond.

Heavily boron-doped, diamond films can become superconducting with critical temperatures Tc well above 4 K. Here we first measure the reflectivity of such a film down to 5 cm(-1), by also using coherent synchrotron radiation. We thus determine the optical gap 2Delta, the field penetration depth lambda, the range of action of the Ferrell-Glover-Tinkham sum rule, and the electron-phonon spectral function alpha2F(omega). We conclude that diamond behaves as a dirty BCS superconductor.

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PubMed2006

Far-infrared absorption of La1-xCaxMnO3-y at high pressure.

The first far-infrared absorption spectra of manganite samples at pressures P up to 10 GPa were obtained on La1-xCaxMnO3-y by use of synchrotron radiation. For x=0.25 and 0.20 (y=0), P promotes partial metallization at room temperature through a strong reduction of the insulating gap. An x=0.20 sample with y=0.08 does not show any charge delocalization effect up to 10 GPa. An Urbach-like model of disordered Jahn-Teller wells is shown to well fit the far-infrared band edge and allows one to obtain a reliable pressure dependence of the energy gap.

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PubMed2005

Temperature dependence of the optical spectral weight in the cuprates: role of electron correlations.

We compare calculations based on the dynamical mean-field theory of the Hubbard model with the infrared spectral weight W(Omega,T) of La(2-x)SrxCuO4 and other cuprates. Without using fitting parameters we show that most of the anomalies found in W(Omega,T) with respect to normal metals, including the existence of two different energy scales for the doping and the T dependence of W(Omega,T), can be ascribed to strong correlation effects.

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PubMed2005

Frequency-dependent thermal response of the charge system and the restricted sum rules of La2-xSrxCuO4.

In La2-xSrxCuO4 (LSCO) the spectral weight W=integralOmega0sigma(ab)1(omega,T)domega [where sigma(ab)1(omega,T) is the ab-plane conductivity] obeys the same law W=W0-BOmegaT2 as in a conventional metal such as gold, for any Omega up to the plasma edge. However, in LSCO BOmega points toward correlation effects and, unlike in gold, is related to an energy scale tT<<t0 approximately W0. The Ferrell-Glover-Tinkham sum rule is fulfilled in LSCO superconductors for Omega greater than or approximately equal to 2000 cm(-1).

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PubMed2003

Phase diagram of La2-xSrxCuO4 probed in the infared: imprints of charge stripe excitations.

While there is increasing evidence for antiferromagnetic (AF) ordering in the Cu-O planes of high-T(c) superconductors, either static or fluctuating, there is no direct evidence so far for the charge stripes that should separate the AF domains. By investigating the optical response of La2-xSrxCuO4 for 0<or=x<or=0.26 and 30<or=T<or=295 K, we identify strong far infrared peaks whose energy, width, and intensity are consistent with a scenario of charge stripe dynamics in the Cu-O planes.

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PubMed2000

Spectral distribution of infrared synchrotron radiation by an insertion device and its edges: A comparison between experimental and simulated spectra

The first measurements of the spectral distribution of infrared radiation emitted by an undulator are reported. They are compared with calculations including both velocity and acceleration terms. Measurements have been performed at the beam line SIRLOIN (Spectroscopie en InfraRouge Lointain). The agreement between the observations and this first exact numerical solution shows that the inclusion of the velocity term in the submillimeter frequency range is necessary. Moreover, structures due to undulator edges are observed in the far infrared and mid-infrared range, while the interference pattern due to redshifted harmonics of the undulator is dominating in the mid-infrared to near infrared.

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PubMed1998

SINBAD, a brilliant IR source from the DAPhiNE storage ring.

SINBAD is the Italian IR synchrotron radiation beamline, designed to work at wavelengths greater than 10 micro m. It is being installed on DAPhiNE, a new collider that is designed to work at 0.51 GeV with a beam current up to 5 A. Due to such a high current, the IR extracted from a bending magnet will be more brilliant than that of a black body at 2000 K by two orders of magnitude at 100 micro m. The beamline optical system, projected by ray-tracing simulation, consists of six mirrors that first focus the radiation on a wedged CVD diamond-film window and then transfer the collimated beam to the experimental area where a Michelson interferometer will be installed.

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PubMed1996