Low-temperature thermal conductivity measurements were performed on single crystal of PbTaSe2, a noncentrosymmetric superconductor with topological bulk nodal lines in the electronic band structure. It is found that the residual linear term κ0/T is negligible in zero magnetic field. Furthermore, the field dependence of κ0/T exhibits a clear "S"-shape curve. These results suggest that PbTaSe2 has multiple nodeless superconducting gaps. Therefore, the spin-triplet state with gap nodes does not play an important role in this noncentrosymmetric superconductor with strong spin-orbital coupling. The fully gapped superconducting state also meets the requirement of a topological superconductor, if PbTaSe2 is indeed the case.

A general feature of unconventional superconductors is the existence of a superconducting dome in the phase diagram as a function of carrier concentration 1 . For the simplest iron-based superconductor FeSe (with transition temperature Tc  8 K) 2 , its Tc can be greatly enhanced by doping electrons via many routes 3-6 , even up to 65 K in monolayer FeSe/SiTiO3 (refs. 7-10). However, a clear phase diagram with carrier concentration for FeSe-derived superconductors is still lacking. Here, we report the observation of a series of discrete superconducting phases in FeSe thin flakes by continuously tuning carrier concentration through the intercalation of Li and Na ions with a solid ionic gating technique 11 . Such discrete superconducting phases are robust against the substitution of Se by 20% S, but are vulnerable to the substitution of Fe by 2% Cu, highlighting the importance of the iron site being intact. A complete superconducting phase diagram for FeSe-derivatives is given, which is distinct from other unconventional superconductors.The discovery of iron-based superconductors sparked a huge renaissance in exploring the mystery of unconventional superconductivity [12][13][14][15] . For the iron arsenides, there always exists a superconducting (SC) dome in the phase diagram, i.e., a continuous increase, maximum, and then decrease of the transition temperature Tc, with charge carrier doping, applied external pressure, or isovalent doping [14][15][16] . Such an

We report low-temperature heat transport measurements on superconducting iron sulfide FeS with Tc ≈ 5 K, which has the same crystal structure and similar electronic band structure to the superconducting iron selenide FeSe. In zero magnetic field, a significant residual linear term κ0/T is observed. At low field, κ0/T increases rapidly with the increase of field. These results provide strong evidence for nodal superconducting gap in FeS. We compare it with the sister compound FeSe, and other iron-based superconductors with nodal gap. arXiv:1511.07717v3 [cond-mat.supr-con]

Low-temperature thermal conductivity measurements were performed on the single crystal of caged-type superconductors Y 5 Rh 6 Sn 18 and Lu 5 Rh 6 Sn 18 down to 80 mK. In zero magnetic field, no residual linear term T 0 k is found for either superconductor. At low field, the T 0 k of these two superconductors shows weak field dependence. These results exclude the nodal superconducting gap in Y 5 Rh 6 Sn 18 as revealed by recent specific heat measurements, and suggest that the caged-type superconductors R 5 Rh 6 Sn 18 (R = Y and Lu) may have a common nodeless superconducting gap.

Topological superconductivity is an exotic phenomenon due to the symmetry-protected topological surface state, in which a quantum system has an energy gap in the bulk but supports gapless excitations conned to its boundary. Symmetries including central and time-reversal, along with their relations with topology, are crucial for topological superconductivity. We report muon spin relaxation/rotation (μSR) experiments on a topological noncentrosymmetric superconductor PbTaSe2 to study its TRS and gap symmetry. Zero-field μSR experiments indicate the absence of internal magnetic eld in the superconducting state, consistent with previous μSR results. Furthermore, transverse-field μSR measurements reveals that the superconducting gap of PbTaSe2 is an isotropic three-dimensional fully-gapped single-band. The fully-gapped results can help understand the pairing mechanism and further classify the topological superconductivity in this system.