Spin Gap inHgBa2Ca2Cu3O8+δSingle Crystals from63Cu NMR

Abstract

We report on ${}^{63}\mathrm{Cu}$ NMR spectra, $T_1$ and $T_{2G}$ measurements in single crystals of underdoped, three-layered, ${\mathrm{HgBa}}_2{\mathrm{Ca}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{8+\delta }$, with $T_c\simeq 115\mathrm{K}$. We show clear evidence for the opening of a spin gap below $T^{*}\simeq 230\mathrm{K}$, the highest temperature reported so far. Also, the characteristic energy of the spin fluctuations is found to be higher than in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$; both features are presumably related to the very high $T_c$ in this compound. Below $T^{*}$, ${}_{}{}^{63}{}_{}{}^{}T_1^{}{}_{}{}^{}$ has the same temperature dependence in the three ${\mathrm{CuO}}_2$ planes, which is difficult to explain within a pure interlayer spin pairing.