SignificanceObservation of a quantum critical point (QCP) in correlated unconventional superconductors has been key to understanding of the intricate relationship between superconductivity and quantum criticality, which has been often hampered by the dome of superconducting (SC) state that veils the T=0 K quantum phase transition. This work demonstrates observation of a QCP in the Al-doped CrAs, where the QCP became completely detached from the dome of superconducting phase. The tuned QCP and its separation from the SC state imply that Cooper pair formation is not mediated solely by critical magnetic fluctuations in CrAs. This work illustrates the potential of using multiple non-thermal parameters to reveal the relationship between superconductivity and a hidden quantum critical point in classes of unconventional superconductors. AbstractThe origin of unconventional superconductivity and its relationship to a T=0 K continuous quantum phase transition (a quantum critical point, QCP), which is hidden inside the dome of a superconducting state, have long been an outstanding puzzle in correlated superconductors. The observation and tuning of the hidden QCP, which is critical in resolving the mystery, however, has been rarely reported due to lack of ideal systems. The helical antiferromagnet CrAs provides an example in which a dome of superconductivity appears at a pressure where its magnetic transition goes to zero temperature. Here we report the tuning of a projected critical point in CrAs via Al chemical doping (Al-CrAs) and separation of the magnetic critical point from the pressure-induced superconducting phase. When CrAs is doped with Al, its AFM ordering temperature T N increases from 260 K to 270 K. With applied pressure, T N decreases and extrapolates to zero Kelvin near 4.5 kbar, which is shifted from 8 kbar for undoped CrAs. A funnel of anomalously enhanced electron scattering and a non-Fermi liquid resistivity underscore an AFM QCP near 4.5 kbar in Al-CrAs. Pressure-induced superconductivity, in contrast, is almost independent of Al doping and forms a dome with essentially the identical maximum T c and same optimal pressure as in pure CrAs. The clear separation between the tuned AFM QCP and T c maximum in Al-CrAs suggests that superconductivity is independent of the AFM QCP, illustrating subtleties in the interplay between superconductivity and quantum criticality in correlated electron systems.

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