Abstract
The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 p 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.
Highlights
The pressure-induced superconductivity in the binary helimagnet CrAs has recently attracted much attention[1,2,3,4,5]
The close proximity of superconductivity to magnetism, the similarity of the phase diagram of CrAs with that of some Fe-based superconductors, as well as the absence of the coherent Hebel-Slichter peak in the nuclear relaxation rate 1/T1T made the authors of Refs 1–3, 5 to suggest an unconventional pairing mechanism
In this paper we report on muon spin rotation studies of the magnetic and the superconducting properties of CrAs
Summary
The pressure-induced superconductivity in the binary helimagnet CrAs has recently attracted much attention[1,2,3,4,5]. The close proximity of superconductivity to magnetism, the similarity of the phase diagram of CrAs with that of some Fe-based superconductors, as well as the absence of the coherent Hebel-Slichter peak in the nuclear relaxation rate 1/T1T made the authors of Refs 1–3, 5 to suggest an unconventional pairing mechanism. It should be noted, that the similarity of the phase diagram does not necessarily requires a similar mechanism of Cooper-pairing. We first discuss separately the magnetic and the superconducting responses as a function of pressure, and concentrate later on the issue of coexistence between magnetism and superconductivity
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