Detection of an Unconventional Superconducting Phase in the Vicinity of the Strong First-Order Magnetic Transition in CrAs Using ^75As-Nuclear Quadrupole Resonance

Abstract

Pressure-induced superconductivity was recently discovered in the binary helimagnet CrAs. We report the results of measurements of nuclear quadrupole resonance for CrAs under pressure. In the vicinity of the critical pressure P_c between the helimagnetic (HM) and paramagnetic (PM) phases, a phase separation is observed. The large internal field remaining in the phase-separated HM state indicates that the HM phase disappears through a strong first-order transition. This indicates the absence of a quantum critical point in CrAs; however, the nuclear spin-lattice relaxation rate 1/T_1 reveals that substantial magnetic fluctuations are present in the PM state. The absence of a coherence effect in 1/T_1 in the superconducting state provides evidence that CrAs is the first Cr-based unconventional superconductor.

6 pages, 7 figures, Revised version + Supplemental Material, to be published in Phys. Rev. Lett

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• Spin-orbit coupling effects on the electronic properties of the pressure-induced superconductor CrAs
• Growth of bulk single-crystal MnP helimagnet and its structural and NMR characterization
• Nonsaturating large magnetoresistance in the high carrier density nonsymmorphic metal CrP
• Resistivity measurements unveil microscopic properties of CrAs
• Low energy bands and transport properties of chromium arsenide
• Anomalous helimagnetic domain shrinkage due to the weakening of Dzyaloshinskii-Moriya interaction in CrAs
• Lattice dynamics in the double-helix antiferromagnet FeP
• Magnetic correlations in the pressure-induced superconductor CrAs investigated by ${}^{75}$As nuclear magnetic resonance
• Dimensionality of the superconductivity in the transition metal pnictide WP