Superconductivity has been first observed in TlNi2Se2 at TC=3.7 K and appears to involve heavy electrons with an effective mass m∗=14∼20 mb, as inferred from the normal state electronic specific heat and the upper critical field, H_C2(T). Although the zero-field electronic specific heat data, Ces(T), in low temperatures (T < 1/4 TC) can be fitted with a gap BCS model, indicating that TlNi2Se2 is a fully gapped superconductor, the two-gap BCS model presents the best fit to all the Ces(T) data below TC. It is also found that the electronic specific heat coefficient in the mixed state, γN(H), exhibits a \textit{H}1/2 behavior, which was also observed in some \textit{s}-wave superconductors, although once considered as a common feature of the \textit{d}-wave superconductors. Anyway, these results indicate that TlNi2Se2, as a non-magnetic analogue of TlFexSe2 superconductor, is a multiband superconductor of heavy electron system.
@article{arxiv.1303.4658,
title = {Multiband Superconductivity of Heavy Electrons in TlNi2Se2 single crystal},
author = {Hangdong Wang and Chiheng Dong and Qianhui Mao and Rajwali Khan and Xi Zhou and Zhenxia Li and Bin Chen and Jinhu Yang and Qiping Su and Minghu Fang},
journal= {arXiv preprint arXiv:1303.4658},
year = {2013}
}