Experimental observation of Bose condensation in high-temperature superconductors

Emission Mössbauer spectroscopy on 67Cu (67Zn) and 67Ga (67Zn) isotopes was used to show that for the superconductors Nd1.85Ce0.15CuO4, La1.85 Sr0.15CuO4, and Tl2Ba2 CaCuO8 in the temperature range T > Tc the temperature dependence of the center of gravity S of the Mössbauer spectrum is determined by the second-order Doppler shift, while in the range T < Tc the Bose condensation of Cooper pairs influences the value of S (here Tc is the superconducting transition temperature). The spatial nonuniformity produced in the electron density by a Bose condensate of Cooper pairs was observed for La1.85 Sr0.15CuO4.