SR a brilliant sources for solid-state researches in the IR and far-IR energy domain 

Augusto Marcelli 

°Laboratori Nazionali Frascati INFN (INFN), Via E. Fermi 40, Frascati 00044, Italy

Abstract

IR spectroscopy probes rotations and vibrations of molecules, low-energy excitations of solids and many other phenomena in condensed matter physics, chemistry, biophysics and materials science. We discuss far and mid-IR spectroscopy and reflectivity measurements of metallic, semiconductor and insulator systems returning accurate information as a function of external parameters such as temperature or pressure. Reflectivity experiments were applied to investigate intrinsic point defects, a characteristic that affects properties of many solid solutions such as HgCdTe. Although limited in sensitivity far-IR reflectivity may be used for a quantitative determination of the vacancy concentration in a lattice thanks to the identification of additional vibrational modes. The same method can be used to identify in a semiconductor O or H impurities that affects crystal properties and limit applications.

Far-IR spectroscopy may be also used to investigate the pressure-driven insulator-to-metal transition, one of the most intriguing phenomena observed in colossal magnetoresistance (CMR) systems. We present high-pressure far-IR absorption measurements on LaCaMnO samples exploiting the unique characteristic of synchrotron radiation emission. The actual path followed by a system towards metallization is peculiar and volume compression affects the delicate balance among existing microscopic interactions. Far-IR spectra of manganites vs. pressure show a shielding of the phonon modes and a strong reduction of the gap, a clear behavior toward a metallic character at RT vs. pressure.

Finally, because the superconducting energy gap is an important parameter, we will show that the best method to measure the gap is the measurement of the optical reflectance in the far-IR region below the transition. We will present reflectance curves addressing a typical metallic response in the new Fe-based layered superconductors that could be attributed to the gap formation in the density of state.

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Presentation: Invited oral at E-MRS Fall Meeting 2008, Symposium J, by Augusto Marcelli
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-07 00:08
Revised:   2009-06-07 00:48
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