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arXiv · 1905.06055

Tuning the distance to a possible ferromagnetic quantum critical point in A2Cr3As3

J. Luo·J. Yang·R. Zhou·Q. G. Mu·T. Liu·Zhi-an Ren·C. J. Yi·Y. G. Shi·Guo-qing Zheng
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Abstract

Although superconductivity in the vicinity of antiferromagnetic (AFM) instability has been extensively explored in the last three decades or so, superconductivity in compounds with a background of ferromagnetic (FM) spin fluctuations is still rare. We report 75As nuclear quadrupole resonance measurements on the A2Cr3As3 family, which is the first group of Cr-based superconductors at ambient pressure, with A being alkali elements. From the temperature dependence of the spin-lattice relaxation rate (1/T1), we find that by changing A in the order of A=Na, Na0.75K0.25, K, and Rb, the system is tuned to approach a FM quantum critical point (QCP). This may be ascribed to the Cr2-As2-Cr2 bond angle that decreases towards 90 degrees, which enhances the FM interaction via the Cr2-As2-Cr2 path. Upon moving away from the QCP, the superconducting transition temperature Tsc increases progressively up to 8.0 K in Na2Cr3As3, which is in sharp contrast to the AFM case where Tsc usually shows a maximum around a QCP. The 1/T1 decreases rapidly below Tsc with no Hebel-Slichter peak, and ubiquitously follows a T5 variation below a characteristic temperature T*=0.6 Tsc, which indicates the existence of point nodes in the superconducting gap function commonly in the family. These results suggest that the A2Cr3As3 family is a possible solid-state analog of superfluid 3He.

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J. Luo, J. Yang, R. Zhou, Q. G. Mu, T. Liu, Zhi-an Ren, C. J. Yi, Y. G. Shi, Guo-qing Zheng. 2019-07-25. Tuning the distance to a possible ferromagnetic quantum critical point in A2Cr3As3. https://doi.org/10.1103/physrevlett.123.047001

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