73Ge- and 135/137Ba-NMR Studies of Clathrate Superconductor Ba24Ge100

概要

論文の詳細を見る
We report on the normal-state properties of a superconducting type-III clathrate compound Ba24Ge100 investigated by 73Ge-NMR at cage sites and by 135/137Ba-NMR at guest sites at ambient pressure ($P=0$) and 2.7 GPa. The measurements of the nuclear spin-lattice relaxation rate $1/T_{1}$ have revealed a significant increase in $1/T_{1}T$ of approximately 200 K at $P=0$, which may be relevant to the rattling motion of Ba atoms in Ge cages. This increase in $1/T_{1}T$ at high temperatures is markedly suppressed at $P=2.7$ GPa. As a result of the suppression of the successive structural transformations, the $1/T_{1}T=\text{const.}$ in a low-temperature regime is increased, proving the increase in the density of states at the Fermi level, $N(E_{\text{F}})$, at $P$. It is this increase in $N(E_{\text{F}})$ that increases the superconducting transition temperature $T_{\text{c}}$ from 0.24 K at $P=0$ to 3.8 K at $P\sim 2.7$ GPa.
Physical Society of Japanの論文
2009-10-15