We report In-NQR and Co-NMR experiments of CeCoIn5 that undergoes a superconducting transition with a record high Tc = 2.3 K to date among heavy-fermion superconductors. At zero magnetic field, an anomalous temperature (T) dependence of nuclear spin-lattice relaxation rate 1/T1 of 115In is explained by the relation 1/T1 ∝ T · χQ(T)3/4 based on the anisotropic spin-fluctuations model in case of the proximity to an antiferromagnetic (AFM) quantum critical point (QCP). The novel behavior of 1/T1 ∼ T 1/4 over a wide T range of Tc < T < 40 K arises because the staggered susceptibility almost follows the Curie law χQ(T) ∝ 1/(T + θ) with θ = 0.6 K and hence 1/T1 ∝ T/(T + 0.6)3/4 ∼ T1/4 for θ < T. We highlight that the behavior 1/T1 ∼ T 1/4 is due to the proximity to the anisotropic AFM QCP relevant with its layered structure, and is not associated with the AFM QCP for isotropic 3D systems. We have also found that the AFM spin fluctuations in CeCoIn5 are suppressed by small magnetic field so that θ = 0.6 K at H = 0 increases to θ = 2.5 K at H = 1.1 T, reinforcing that CeCoIn5 is closely located at the QCP.
|ジャーナル||journal of the physical society of japan|
|出版ステータス||Published - 9月 2003|
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