Low-Temperature Phase Transition in Bi2Sr2Ca(NixCu1−x)208: Evidence for Unconventional Superconductivity
نویسندگان
چکیده
We report the discovery of a low-temperature phase transition in Bi2Sr2Ca(NixCu1−x)208 high temperature superconductor. This transition manifests itself as a sharp reduction of the thermal conductivity of the samples at a temperature T∗c ≈ 200 mK. The temperature dependence of the thermal conductivity changes dramatically from T with α between 1.6 and 1.75 above the transition to T-linear behavior below the transition. Application of a small magnetic field suppresses the low-temperature phase. We interpret this behavior as a phase transition into a second bulk low-temperature superconducting state in which the time-reversal symmetry is likely to be broken. This discovery constitutes direct evidence for unconventional superconductivity in high temperature superconductors. PACS number(s) 74.72.Bk, 74.25.Fy, 74.62.Fj Typeset using REVTEX
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