Due to the strong reactivity of alkaline metals and the easy formation of the impurity phase, the superconducting transition temperature (T c ) of alkaline metals intercalated FeSe is usually limited to 45 K. To avoid the formation of impurity and improve the T c , we intercalate a more chemically inert organic ion (rather than the chemically reactive alkaline metals) into FeSe single crystal in this report. A new FeSe-based superconductor, namely (TBA) 0.3 FeSe, with T c of 50 K, is synthesized by intercalating FeSe single crystal with organic ion tetrabutyl ammonium (TBA + ) via an electrochemical intercalation method, which has the highest T c among FeSe-based bulk superconductors. The structure of the organic ion intercalated product consists of the alternate stacking of monolayer FeSe and the organic molecule. The superconductivity of (TBA) 0.3 FeSe is confirmed by both the magnetic susceptibility and the transport measurement. It is suggested that the chemically inert organic ion should play a key role in the enhancement of T c by avoiding the formation of impurity and disorder in FeSe plane as possible. We also suggest that the TBA + intercalated FeSe with well defined shape and higher T c offer a good playground for further bulk measurement investigation.

The controllable manipulation of materials properties has always attracted broad interests since there exists the possibility to identify the relationship between different electronic states, and even discover new states. Here we report the electrochemical intercalation of cetyltrimethylammonium (CTA + ) into 2H-TaS 2 . The single layer TaS 2 is intercalated with CTA + cations and the direction of CTA + is approximately perpendicular to the lamellar structure of TaS 2 . With this facile and efficient method, the superconducting transition temperature (T c ) of pristine TaS 2 increases from 0.8 K to the maximum 3.7 K, showing a dome-like behavior. The Hall coefficient measurement indicates that the intercalated CTA + cations introduce electrons to this system. The present results demonstrate that electrochemical intercalation method is effective in tuning the materials properties and may pave the way for exploring new superconductors.

We study the normal-state transport properties of AFe2As2 (A  =  K, Rb and Cs) single crystals using Hall coefficient, resistivity and magnetoresistance (MR) measurements. In all three materials, the Hall coefficient R H shows a strong temperature dependence, which is typical for multi-band systems. In particular, R H develops an upturn below a characteristic temperature [Formula: see text], which is in agreement with the incoherence-coherence crossover reported in recent nuclear magnetic resonance studies. A Fermi-liquid-like state, characterized by T (2) behavior of the resistivity and a positive orbital MR obeying Kohler's rule, emerges below T FL  ∼0.4 [Formula: see text]. The superconducting transition temperature T c experiences a simultaneous suppression with [Formula: see text] and T FL as the alkali ion's radius increases from A  =  K to A  =  Cs, suggesting that the unconventional superconductivity in the AFe2As2 series is related to the strength of the electronic coherence. A phase diagram, similar to that in the heavy fermion Kondo lattice system, is obtained. Based on all the experimental evidence, we argue that the physical properties of this family of heavily hole-doped Fe-based superconductors are controlled by the hybridization between itinerant carriers and localized orbitals, and the Kondo scenario could be effective in such a case.