Pressure effect on optical conductivity for bulk (Bi,Pb)-2223 samples

We report on optical conductivity (in the range from 230 nm to 900 nm) of single phase bulk (Bi,Pb)-2223 superconductor samples (pressed isostatically at 200 MPa and 150 MPa and pressed uniaxially at 40 MPa and at 20 MPa), above and below the transition temperature. The reflectance spectrum, performed with an Ocean Optics Spectrometer S-2000 UVVIS by using a detector CCD with an Interface ADC500, shows the so called 'transparency of the metals in ultraviolet' in normal as well in superconducting states only for the sample pressed at 20 MPa and 40 MPa. Under the critical temperature a different feature with some spectacular peaks in UV range of reflectance spectrum has been observed in the case of samples pressed isostatically at 200 MPa and 150 MPa. If T < T. it is also observed a linear increasing of plasma frequency versus the pressure, that was apprehended by a similar pressure dependence of critical temperatures (appreciated by diamagnetic transition). The shape of optical conductivity in visible range is consistent with the theoretical mechanisms that assume the existence of large polaronic carriers.