Superconductivity in Layered Pnictides BaRh2P2 and BaIr2P2

Bulk superconductivity was discovered in BaRh 2 P 2 ( T c =1.0 K) and BaIr 2 P 2 ( T c =2.1 K), which are isostructural to (Ba,K)Fe 2 As 2 , indicative of the appearance of superconductivity over a wide variety of layered transition metal pnictides. The electronic specific heat coefficient γ in the normal state, 9.75 and 6.86 mJ/(mol K 2 ) for BaRh 2 P 2 and BaIr 2 P 2 respectively, indicate that the electronic density of states of these two compounds are moderately large but smaller than those of Fe pnictide superconductors. The Wilson ration R W =χ/γ×π 2 k B 2 /3 µ B 2 close to 1 indeed implies the absence of strong electron correlations and magnetic fluctuations unlike Fe pnictides.