Experimental observation of Bose condensation in high-temperature superconductors

Emission Mossbauer spectroscopy on Cu-67 (Zn-67) and Ga-67 (Zn-67) isotopes was used to show that for the superconductors Nd1.85Ce0.15CuO4, La1.85Sr0. 15CuO4, and Tl2Ba2CaCuO8 in the temperature range T > T-c the temperature d ependence of the center of gravity S of the Mossbauer spectrum is determine d by the second-order Doppler shift, while in the range T < T-c the Bose co ndensation of Cooper pairs influences the value of S (here T-c is the super conducting transition temperature). The spatial nonuniformity produced in t he electron density by a Bose condensate of Cooper pairs was observed for L a1.85Sr0.15CuO4. (C) 2000 MAIK "Nauka/Interperiodica".