Low-temperature phase transition in Bi2Sr2Ca(Cu1-xNix)(2)O-8

We report on the discovery of a low-temperature phase transition in Bi2Sr2C a(NixCu1-x)(2)O-8 high temperature superconductor. This transition manifest s itself as a sharp reduction of the thermal conductivity of the samples at a temperature T-c* approximate to 200 mK. The temperature dependence of th e thermal conductivity changes dramatically from nearly quadratic above the transition to T-linear behavior below the transition. Application of a sma ll magnetic field suppresses the low-temperature phase. Such behavior is co nsistent with appearance of a second bulk low-temperature superconducting s tate at T-c*. (C) 1998 Elsevier Science Ltd. All rights reserved.