Progress in Superconductivity

The Korean Superconductivity Society (한국초전도학회)
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$^{13}C$ Nuclear Magnetic Resonance Study of Graphite Intercalated Superconductor $CaC_6$ Crystals in the Normal State

$CaC_6$ 결정에 대한 정상상태에서의 $^{13}C$ 핵자기공명 측정

  • Kim, Sung-Hoon (Department of Physics, Konkuk University) ;
  • Kang, Ki-Hyeok (Department of Physics, Konkuk University) ;
  • Mean, B.J. (Department of Physics, Konkuk University) ;
  • Ndiaye, B. (Department of Physics, Konkuk University) ;
  • Lee, Moo-Hee (Department of Physics, Konkuk University) ;
  • Kim, Jun-Sung (Department of Physics, Pohang University of Science and Technology)
  • Received : 2010.09.06
  • Accepted : 2010.10.13
  • Published : 2010.10.31
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Abstract

$^{13}C$ NMR (nuclear magnetic resonance) measurements have been performed to investigate the local electronic structure of a superconducting graphite intercalation compound $CaC_6$ ($T_c$ = 11.4 K). A large number of single crystals were stacked and sealed in a quartz tube for naturally abundant $^{13}C$ NMR. The spectrum, Knight shift, linewidth, and spin-lattice relaxation time $T_1$ were measured in the normal state as a function of temperature down to 80 K at 8.0 T perpendicular to the c-axis. The $^{13}C$ NMR spectrum shows a single narrow peak with a very small Knight shift. The Knight shift and the linewidth of the $^{13}C$ NMR are temperature-independent around, respectively, +0.012% and 1.2 kHz. The spin-lattice relaxation rate, $1/T_1$, is proportional to temperature confirming a Korringa behavior as for non-magnetic metals. The Korringa product is measured to be $T_1T\;=\;210\;s{\cdot}K$. From this value, the Korringa ratio is deduced to be $\xi$ = 0.73, close to unity, which suggests that the independent-electron description works well for $CaC_6$, without complications arising from correlation and many-body effects.

Keywords

References

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