Abstract
The origin of unconventional superconductivity and its relationship to a T = 0 K quantum critical point (QCP), which is hidden inside the dome of a superconducting state, have long been an outstanding puzzle in strongly correlated superconductors. The observation and tuning of the hidden QCP, which is key to resolving the mystery, however, has been rarely reported. Here we report the controlling of a hidden QCP in the helical antiferromagnet CrAs and separation of the tuned QCP from the pressure-induced superconducting phase. The Al doping in CrAs increases the antiferromagnetic ordering temperature TN from 265 to 275 K, while it suppresses the QCP from 8 to 4.5 kbar. Pressure-induced superconductivity in the high-pressure regime is almost independent of Al doping, but superconductivity below 6 kbar is suppressed, revealing the clear separation between the tuned antiferromagnetic QCP and Tc maximum. These discoveries illustrate subtleties in the interplay between superconductivity and quantum criticality and warrant a deeper insight in understanding of unconventional superconductivity.
Highlights
Unconventional superconductivity commonly emerges in proximity to a magnetically ordered phase, raising the possibility that critical spin fluctuations may mediate the formation of superconducting (SC) Cooper pairs.[1,2,3,4,5,6,7,8,9,10] In the vast majority of these cases, as sketched in Fig. 1a, the zero-temperature limit of a continuous magnetic phase boundary (a quantum critical point (QCP)) is veiled by a dome of superconductivity, making it difficult to prove the interplay between unconventional superconductivity and fluctuations arising from the presumed QCP
Unusual normal state properties of these materials above their dome of superconductivity imply that a magnetic QCP may remain a viable concept even below Tc in various classes of unconventional superconductors, such as those based on Fe and Cu as well as heavy fermion compounds, in which there is an intricate interplay among intertwined order parameters.[11,12,13,14]
Though weak diamagnetism and zero resistance appear already at pressures near 3 kbar, the highest Tc occurs near the critical pressure of 8 kbar where the coupled magnetic/structural transition is projected to zero Kelvin and electrical resistivity deviates from the Landau–Fermi liquid T2 dependence, indicating a helical antiferromagnetic (AFM) QCP hidden below the dome of pressure-induced superconductivity in CrAs.[19,20,21,22]
Summary
Unconventional superconductivity commonly emerges in proximity to a magnetically ordered phase, raising the possibility that critical spin fluctuations may mediate the formation of superconducting (SC) Cooper pairs.[1,2,3,4,5,6,7,8,9,10] In the vast majority of these cases, as sketched in Fig. 1a, the zero-temperature limit of a continuous magnetic phase boundary (a quantum critical point (QCP)) is veiled by a dome of superconductivity, making it difficult to prove the interplay between unconventional superconductivity and fluctuations arising from the presumed QCP.
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