We report superconductivity in novel iron-based compounds Ca 10 (Pt n As 8 )(Fe 2Àx Pt x As 2 ) 5 with n ¼ 3 and 4. Both compounds crystallize in triclinic structures (space group P 1), in which Fe 2 As 2 layers alternate with Pt n As 8 spacer layers. Superconductivity with a transition temperature of 38 K is observed in the n ¼ 4 compound with a Pt content of x ' 0:36 in the Fe 2 As 2 layers. The compound with n ¼ 3 exhibits superconductivity at 13 K.

SrPt 2 As 2 is a novel arsenide superconductor, which crystallizes in the CaBe 2 Ge 2 -type structure as a different polymorphic form of the ThCr 2 Si 2 -type structure. SrPt 2 As 2 exhibits a charge-density-wave (CDW) ordering at about 470 K and enters into a superconducting state at T c ¼ 5:2 K. The coexistence of superconductivity and CDW refers to Peierls instability with a moderately strong electron-phonon interaction. Thus SrPt 2 As 2 can be viewed as a nonmagnetic analog of iron-based superconductors, such as doped BaFe 2 As 2 , in which superconductivity emerges in close proximity to spin-density-wave ordering.KEYWORDS: non-iron-based pnictide, superconductivity, charge-density wave, SrPt 2,3) BaFe 2 As 2 is the compound most studied among the iron-based families so far and is widely thought to represent the generic features of the iron-based superconductors.2,3) BaFe 2 As 2 exhibits AFM ordering below T N ¼ 140 K.4) The partial chemical substitution of either Ba, Fe, or As ions with a different element suppresses the AFM ordering and induces superconductivity.5-8) The maximum superconducting transition temperature, T c ¼ 38 K for (Ba 1Àx K x )Fe 2 As 2 , 5) is obtained near the critical concentration where AFM ordering is completely suppressed.It has been widely thought that AFM ordering in ironbased superconductors originates from the spin-densitywave (SDW) instability due to the nesting of two Fermi pockets, a hole pocket centered at the À point and an electron pocket centered at the M point, which are connected by the nesting vector Q ¼ ð; Þ.9-12) This characteristic electronic structure is believed to be a key ingredient of the high-temperature superconductivity due to AFM spin fluctuations in iron-based families. 2,3,13,14) Moreover, it has been theoretically proposed that the nesting determines the symmetry of Cooper pairs in the iron-based superconductors, in which a node locates either away from the Fermi surfaces (s AE -wave) 13,14) or directly at the Fermi surface (d-wave).14)The charge-density-wave (CDW) instability is another consequence of Fermi-surface nesting when electron-phonon interaction remains important. CDW ordering, as well as SDW ordering, competes with or coexists with superconductivity. [15][16][17][18][19][20] In this letter, we demonstrate that superconductivity at T c ¼ 5:2 K coexists with CDW in platinumbased 122 arsenide SrPt 2 As 2 . The superconducting transition temperature of SrPt 2 As 2 is considerably high compared with those of other non-iron-based 122 arsenides such as SrNi 2 As 2 (T c ¼ 0:62 K) 21) and BaNi 2 As 2 (T c ¼ 0:7 K). 22)Our observation suggests that Fermi-surface nesting is a key ingredient of the relatively high superconducting transition temperature of SrPt 2 As 2 . SrPt 2 As 2 crystallizes in a tetragonal CaBe 2 Ge 2 -type structure with the space group P4=nmm (#129), 23) as shown in Fig. 1(a). The structure is different from another polymorphic form of 122, a ThCr 2 Si 2 -type structure with the space group I4=mmm (#139), in which BaFe 2 As 2 cryst...

We report superconductivity in the honeycomb-lattice pnictide SrPtAs with Tc = 2.4 K. To our knowledge, SrPtAs is the first superconducting pnictide with a honeycomb lattice structure. Our finding opens up new playground to develop pnictide superconductors with honeycomb lattices, in addition to square lattices known in iron-based superconductors.Comment: 2 pages, 3 figure