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We investigated a high-quality MgB$_{2}$ thin film with a thickness of $sim$1000 nm on an Al$_{2}$O$_{3}$ substrate using optical spectroscopy. We measured the reflectance spectra of the film at various temperatures both below, and above, the superconducting transition temperature, $T_c$ $simeq$ 40 K. An earlier study showed that when the sample surface is exposed to air the optical properties of the surface change immediately, however, the saturated change is negligibly small in the far-infrared region. The optical conductivity spectrum in the normal state shows two (narrow and broad) Drude modes, with the narrow Drude mode being dominant in the low frequency region below 1000 cm$^{-1}$. Our study, which uses a good-quality sample, provides more reliable data on the optical properties of MgB$_2$, in a similar spectral range. The optical data is analyzed further using an extended Drude model, and the electron-phonon spectral density function, $alpha^2F(omega)$, is extracted. The spectral density function $alpha^2F(omega)$ features two peaks: a small one near 114 cm$^{-1}$, and a strong peak around the 550 cm$^{-1}$ where the B-B bond stretching phonon exists. Our data in the superconducting state does not show the expected energy shift of the onset of scattering associated with the $alpha^2F(omega)$ peaks.
We report results of dc magnetic and ac linear low-frequency study of a polycrystalline MgB$_2$ sample. AC susceptibility measurements at low frequencies, performed under dc fields parallel to the sample surface, provide a clear evidence for surface superconducting states in MgB$_2$.
We report on the results of a comparative investigation of highly dense bulk MgB$_2$ samples prepared by three methods: (i) hot deformation; (ii) high pressure sintering; and (iii) mechanical alloying of Mg and B powders with subsequent hot compactio
We demonstrate that Ta sheathed SmO1-xFxFeAs wires were successfully fabricated by the powder-in-tube (PIT) method for the first time. Structural analysis by mean of x-ray diffraction shows that the main phase of SmO1-xFxFeAs was obtained by this syn
We present studies of the photoexcited quasiparticle dynamics in Tl$_{2}$Ba$_{2}$Ca$_{2}$Cu$_{3}$O$_{y}$ (Tl-2223) using femtosecond optical techniques. Deep into the superconducting state (below 40 K), a dramatic change occurs in the temporal dynami
In- and out-of-plane optical spectra and specific heat measurements for the single layer cuprate superconductor Hg-1201 at optimal doping (Tc = 97 K) are presented. Both the in-plane and out-of-plane superfluid density agree well with a recently prop