Magnetic and superconducting properties of an S-type single-crystal CeCu2Si2 probed by (63)Cu nuclear magnetic resonance and nuclear quadrupole resonance

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  • Magnetic and superconducting properties of an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>S</mml:mi></mml:math> -type single-crystal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>CeCu</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Si</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> probed by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Cu</mml:mi><mml:mprescripts/><mml:none/><mml:mn>63</mml:mn></mml:mmultiscripts></mml:math> nuclear magnetic resonance and nuclear quadrupole resonance

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We have performed $^{63}$Cu nuclear magnetic resonance/nuclear quadrupole resonance measurements to investigate the magnetic and superconducting (SC) properties on a "superconductivity dominant" ($S$-type) single crystal of CeCu$_2$Si$_2$. Although the development of antiferromagnetic (AFM) fluctuations down to 1~K indicated that the AFM criticality was close, Korringa behavior was observed below 0.8~K, and no magnetic anomaly was observed above $T_{\rm c} \sim$ 0.6 K. These behaviors were expected in $S$-type CeCu$_2$Si$_2$. The temperature dependence of the nuclear spin-lattice relaxation rate $1/T_1$ at zero field was almost identical to that in the previous polycrystalline samples down to 130~mK, but the temperature dependence deviated downward below 120~mK. In fact, $1/T_1$ in the SC state could be fitted with the two-gap $s_{\pm}$-wave rather than the two-gap $s_{++}$-wave model down to 90~mK. Under magnetic fields, the spin susceptibility in both directions clearly decreased below $T_{\rm c}$, indicative of the formation of spin singlet pairing. The residual part of the spin susceptibility was understood by the field-induced residual density of states evaluated from $1/T_1T$, which was ascribed to the effect of the vortex cores. No magnetic anomaly was observed above the upper critical field $H_{c2}$, but the development of AFM fluctuations was observed, indicating that superconductivity was realized in strong AFM fluctuations.

10 pages, 8 figures

Journal

  • Physical Review B

    Physical Review B 96 (13), 2017-10

    American Physical Society (APS)

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