Hangdong Wang, Chiheng Dong, Qianhui Mao, Rajwali Khan, Xi Zhou, Zhenxia Li, Bin Chen, Jinhu Yang, Minghu Fang
Superconductivity has been first observed in TlNi$_2$Se$_2$ at \textit{T}$_C$=3.7 K and appears to involve heavy fermion quasi-particles with an effective mass $m^*$=14$\sim$20 $m_e$, as inferred from the normal state electronic specific heat and the upper critical field, $H_{C2}(T)$. However, the magnitude of the superconducting specific heat jump at $T_C$, zero-field electronic specific heat in superconducting state, $C_{es}(T)$, indicate that TlNi$_2$Se$_2$ seem to be a fully gapped superconductor, similar to that in the other Ni-arsenide compounds, but different with that in the standard heavy fermion \textit{f}-electron compounds. It was found that the electronic specific heat coefficient in the mixed state, $\gamma_N(H)$, exhibits a \textit{H}$^{1/2}$ behavior, which was once considered as a common feature of the \textit{d}-wave superconductors, but also observed in some conventional \textit{s}-wave superconductors. These results indicate that TlNi$_2$Se$_2$, as a non-magnetic analogue of TlFe$_x$Se$_2$ superconductor, is an example of \textit{s}-wave superconductor of heavy-fermion system.
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http://arxiv.org/abs/1303.4658
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