Pressure Induced Superconductivity on the border of Magnetic Order in MnP

We report the discovery of superconductivity on the border of long-range magnetic order in the itinerant-electron helimagnet MnP via the application of high pressure. Superconductivity with $T_{\text{sc}}\approx 1\mathrm{K}$ emerges and exists merely near the critical pressure $P_c\approx 8\mathrm{GPa}$, where the long-range magnetic order just vanishes. The present finding makes MnP the first Mn-based superconductor. The close proximity of superconductivity to a magnetic instability suggests an unconventional pairing mechanism. Moreover, the detailed analysis of the normal-state transport properties evidenced non-Fermi-liquid behavior and the dramatic enhancement of the quasiparticle effective mass near $P_c$ associated with the magnetic quantum fluctuations.

Figure 1

(a) Resistivity $\rho (T)$ and (b) the temperature derivative $d\rho /dT$ of the MnP single crystal under various pressures up to 10.7 GPa highlighting the variation with pressure of the magnetic transition indicated by the vertical arrows. (c) The $c$-axis ${\rho }_c(T)$ data at low temperatures highlighting the evolution with pressure of the double helical transition at $T_s$. (d) Temperature dependence of the ac magnetic susceptibility ${\chi }^{\prime }(T)$ measured under various pressures, which evidences the appearance of a new magnetic transition at $T^{*}$.

Figure 2

Temperature dependence of (a) the resistivity $\rho (T)$ and (b) the ac magnetic susceptibility $4\pi \chi$ on MnP at low temperatures under various pressures near the critical pressure.

Figure 3

Temperature dependence of (a) ac magnetic susceptibility $4\pi \chi$ and (b) resistivity $\rho (T)$ under different magnetic fields at 7.8 GPa. (c) Temperature dependence of the upper critical field ${\mu }_0{H}_{\mathrm{c}2}$ for MnP at 7.8 GPa. The solid line in (c) is a linear fitting, which gives ${\mu }_0{H}_{\mathrm{c}2}(0)=0.33(1)\mathrm{T}$, and a slope $-0.34(1)\mathrm{T}/\mathrm{K}$.

Figure 4

(a) Pressure dependences of the magnetic transition temperatures, $T_C$, $T_m$, $T^{*}$, $T_s$, and the superconducting transition temperature $T_{sc}$; $T_{\text{sc}}$ has been scaled by a factor of 20 for clarity. (b),(c) Variation with pressure of the residual resistivity ${\rho }_0$ and the $A$ coefficient extracted from a linear fitting to the $\rho (T^2)$ curves at the low-temperature limit. Inset of (a) shows the low-temperature resistivity data at 8.1 GPa in the form of $\rho$ versus $T^{1.5}$. The relatively large error bar for $T^{*}$ in (a) reflects the two-step feature evidenced in the ac magnetic susceptibility in Fig. 1.