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Low-Temperature Phase Transition in Bi_2Sr_2Ca(Ni_xCu_{1-x})_20_8: Evidence for Unconventional Superconductivity

R. Movshovich·M. A. Hubbard·M. B. Salamon·A. V. Balatsky·R. Yoshizaki·J. L. Sarrao
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Abstract

We report the discovery of a low-temperature phase transition in Bi_2Sr_2Ca(Ni_xCu_{1-x})_20_8 high temperature superconductor. This transition manifests itself as a sharp reduction of the thermal conductivity of the samples at a temperature of T_c* \approx 200 mK. The temperature dependence of the thermal conductivity changes dramatically from T^αwith αbetween 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.

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R. Movshovich, M. A. Hubbard, M. B. Salamon, A. V. Balatsky, R. Yoshizaki, J. L. Sarrao. 1997-09-04. Low-Temperature Phase Transition in Bi_2Sr_2Ca(Ni_xCu_{1-x})_20_8: Evidence for Unconventional Superconductivity. https://arxiv.org/abs/cond-mat/9709061

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