Pressure-induced enhancement of superconductivity and quantum criticality in the 12442-type hybrid-structure superconductor KC a2 F e4 A s4 F2

We report a domelike superconductivity and quantum criticality in the 12442-type hybrid-structure superconductor KCa2Fe4As4F2 under hydrostatic pressures up to 15 GPa. It is found that the superconducting transition temperature (Tc) increases from ∼33.5K at ambient pressure to a maximum of ∼36.5K at 2 GPa in the background of enhanced resistivity of the (K,Rb,Cs)Ca2Fe4As4F2 at ambient pressure (AP), and then shows a slope change near 8 GPa with anomalous characteristics of resistivity. Tc is found to be inversely proportional to the characteristic temperature of the coherence-incoherence crossover. The plots of resistivity at various temperatures and pressures and high-pressure x-ray diffraction confirm no pressure-induced half collapse of the tetragonal structure below 15 GPa. The pressure-induced crossover from non-Fermi liquid (the temperature exponent n∼1.05±0.1 at AP) to Fermi liquid (n∼1.92±0.1 at 15 GPa) is accompanied by the reduction of the linear temperature coefficient of normal-state resistivity, nearly two orders of magnitude compared to AP. These characteristics are ascribed to the weakening electronic correlation and/or critical fluctuations by pressure.