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Microscopic measurements in La-NQR of the ternary carbide superconductor LaNiC2
Authors:Y Iwamoto  Y Iwasaki  K Ueda  T Kohara
Institution:

Department of Material Science, Faculty of Science, Himeji Institute of Technology, Ako-gun, Hyogo 678-1297, Japan

Abstract:139La-NQR measurements have been carried out in the ternary carbide superconductor LaNiC2. The nuclear quadrupole frequency and the asymmetry parameter of 139La in LaNiC2 were estimated to be about 1.9 MHz and 0, respectively. In the normal state, the nuclear spin relaxation rate (1/T1) in the 139La NQR signal was proportional to temperature (T) in zero external field above the superconducting transition temperature (Tc) or in an external field larger than the superconducting critical field, which means the system is in the Fermi-liquid state. In the superconducting state, on the other hand, 1/T1 decreases no more linearly with T, but decreases rapidly exponentially as exp (?Δ/kBT) at low T with an appreciable enhancement just below Tc. The value of the superconducting energy gap, 2Δ, was estimated to be 3.34kBTc, compared with 3.52kBTc of the BCS-value. This result strongly suggests that the superconductivity in LaNiC2 is of a conventional BCS type.
Keywords:Ternary carbide superconductor  LaNiC2  NQR  Nuclear spin relaxation rate
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