Two distinct superconducting states inKFe2As2under high pressure

We report measurements of ac magnetic susceptibility ${\ensuremath{\chi}}_{\text{ac}}$ and de Haas--van Alphen (dHvA) oscillations in ${\mathrm{KFe}}_{2}$${\mathrm{As}}_{2}$ under high pressure up to 24.7 kbar. The pressure dependence of the superconducting transition temperature ${T}_{c}$ changes from negative to positive across ${P}_{c}\ensuremath{\sim}18$ kbar, as previously reported. The ratio of the upper critical field to ${T}_{c}$, i.e., ${B}_{c2}/{T}_{c}$, is enhanced above ${P}_{c}$, and the shape of the ${\ensuremath{\chi}}_{\text{ac}}$ versus field curves qualitatively changes across ${P}_{c}$. dHvA oscillations smoothly evolve across ${P}_{c}$, indicating no drastic change in the Fermi surface up to 24.7 kbar. Three dimensionality increases with pressure, while effective masses show decreasing trends. We suggest a crossover from a nodal to a full-gap $s$ wave as a possible explanation.