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

摘要

Pressure-induced superconductivity was recently discovered in the binaryhelimagnet CrAs. We report the results of measurements of nuclear quadrupoleresonance for CrAs under pressure. In the vicinity of the critical pressure P_cbetween the helimagnetic (HM) and paramagnetic (PM) phases, a phase separationis observed. The large internal field remaining in the phase-separated HM stateindicates that the HM phase disappears through a strong first-order transition.This indicates the absence of a quantum critical point in CrAs; however, thenuclear spin-lattice relaxation rate 1/T_1 reveals that substantial magneticfluctuations are present in the PM state. The absence of a coherence effect in1/T_1 in the superconducting state provides evidence that CrAs is the firstCr-based unconventional superconductor.