Detection of an Unconventional Superconducting Phase in the Vicinity of   the Strong First-Order Magnetic Transition in CrAs Using ^75As-Nuclear   Quadrupole Resonance
  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. 
Hisashi Kotegawa, Shingo Nakahara, Rui Akamatsu, Hideki Tou, Hitoshi   Sugawara, and Hisatomo Harima
cond-mat.supr-con cond-mat.str-el