Coexistence of Superconductivity and Antiferromagnetism in Multilayered High-$T_c$ Superconductor HgBa${}_2$Ca${}_4$Cu${}_5$O${}_y$: A Cu-NMR Study

We report a coexistence of superconductivity and antiferromagnetism in five-layered compound HgBa${}_2$Ca${}_4$Cu${}_5$O${}_y$ (Hg-1245) with $T_c=108$ K, which is composed of two types of CuO${}_2$ planes in a unit cell; three inner planes (IP’s) and two outer planes (OP’s). The Cu-NMR study has revealed that the optimallydoped OP undergoes a superconducting (SC) transition at $T_c=108$ K, whereas the three underdoped IP’s do an antiferromagnetic (AF) transition below $T_N\sim$ 60 K with the Cu moments of $\sim (0.3-0.4){\mu }_B$. Thus bulk superconductivity with a high value of $T_c=108$ K and a static AF ordering at $T_N=60$ K are realized in the alternating AF and SC layers. The AF-spin polarization at the IP is found to induce the Cu moments of $\sim 0.02{\mu }_B$ at the SC OP, which is the AF proximity effect into the SC OP.