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$$^{59}$$Co NMR shift anomalies and spin dynamics in the normal state of superconducting CeCoIn$$_5$$; Verification of two-dimensional antiferromagnetic spin fluctuations

超伝導体CeCoIn$$_5$$の通常状態における$$^{59}$$Co核核磁気共鳴シフト異常とスピンダイナミクス; 二次元反強磁性スピン相関の検証

酒井 宏典  ; Baek, S.-H.*; Brown, S. E.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Sakai, Hironori; Baek, S.-H.*; Brown, S. E.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

CeCoIn$$_5$$における反強磁性スピン揺らぎを調べるために$$^{59}$$Co核核磁気共鳴(NMR)実験を行った。NMRシフト($$K$$)と帯磁率($$chi$$)とのプロットが直線上にならない異常が観測される。この$$K$$-$$chi$$異常を温度依存する超微細結合定数$$A(T)$$で総合的に理解できることを示した。$$^{59}$$Co核NMR緩和率の温度依存性は、$$A(T)^2$$でノーマライズするとIn(1)核核四重極緩和率の温度依存性と一致して、矛盾がなくなる。そのスピンダイナミクスは、量子臨界点に近い二次元反強磁性相関で理解できる。また、40K以下で重い電子状態形成と同時にスピン揺らぎの異方性が発達することもわかった。

We have measured the Knight shifts ($$K$$) and nuclear relaxation times ($$T_1$$) for $$^{59}$$Co in CeCoIn$$_5$$ under external fields along a and c axes with the goal of establishing the anisotropy of antiferromagnetic (AFM) spin fluctuations (SF). In our approach, we revisit the problem of interpreting anomalies in the relationship between Knight shift $$K_{a,c}$$ and static susceptibility $$chi_{a,c}$$: assuming a single component susceptibility implies a temperature-dependent hyperfine coupling $$A_{a,c}(T)$$. Once adopted, a known discrepancy between the behaviors of $$T_1^{-1}$$ for $$^{59}$$Co and $$^{115}$$In(1) sites is eliminated to within experimental uncertainties and the variation with temperature is analyzed within the framework of two-dimensional AFM SF in proximity to a quantum-critical point. Moreover, the ratio $$[T_{1a}/T_{1c}]$$ indicates easy-plane anisotropy for $$T<T^{*}sim$$ 40 K, for the heavy-fermion state.

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パーセンタイル:55.9

分野:Materials Science, Multidisciplinary

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