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

TL;DR

This study uses ^75As-NQR measurements to explore pressure-induced superconductivity in CrAs, revealing an unconventional superconducting phase near a first-order magnetic transition without a quantum critical point.

Contribution

It provides the first evidence of an unconventional superconducting phase in CrAs near a strong first-order magnetic transition using nuclear quadrupole resonance.

Findings

Phase separation near critical pressure P_c

Absence of quantum critical point in CrAs

Evidence of unconventional superconductivity in CrAs

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.