LOW-ENERGY EXCITATIONS IN CRYSTALLINE PEROVSKITE OXIDES : EVIDENCE FROM NOISE EXPERIMENTS

In this paper we report measurements of 1/f noise in a crystalline metallic oxide with perovskite structure down to 4.2 K. The results show existence of localized excitations with average activation energy approximate to 70-80 meV which produce a peak in the noise at T approximate to 35-40 K. Ln addition, it shows clear evidence of tunnelling-type two-level systems las in glasses) which show up in noise measurements below 30 K.