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arXiv · 1807.09683

Temperature dependence of NMR Knight shift in pnictides: proximity to a van Hove singularity

R. Nourafkan·S. Acheche
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Abstract

The unconventional temperature variation of the Knight shift (static spin susceptibility) that has been observed in Fe-based superconductors AFe$_2$As$_2$ (A = K, Rb, Cs) is explained in terms of proximity to a van Hove singularity. Using the Hubbard model we show that when the Fermi energy is in the vicinity of a van Hove singularity, a downturn in spin susceptibility occurs as the temperature is lowered. This behavior is characterized by a temperature, $T^*$, which is determined by the difference in energy between the Fermi level and the van Hove singularity. When vertex corrections are taken into account in a dynamical mean-field approximation, the effect of correlations amplifies the relative drop in the Knight shift and moves $T^*$ to lower temperatures.

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R. Nourafkan, S. Acheche. 2018-07-25. Temperature dependence of NMR Knight shift in pnictides: proximity to a van Hove singularity. https://doi.org/10.1103/physrevb.98.161116

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