Pressure-Induced Superconductivity in Flat-Band Kagome Compounds Pd_3P_2(S_1-xSe_x)_8

We performed high-pressure transport studies on the flat-band Kagome compounds, Pd_3P_2(S_1-xSe_x)_8 (x=0, 0.25), with a diamond anvil cell. For both compounds, the resistivity exhibits an insulating behavior with pressure up to 17 GPa. With pressure above 20 GPa, a metallic behavior is observed at high temperatures in Pd_3P_2S_8, and superconductivity emerges at low temperatures. The onset temperature of superconducting transition T_\rm C rises monotonically from 2 K to 4.8 K and does not saturate with pressure up to 43 GPa. For the Se-doped compound Pd_3P_2(S_0.75Se_0.25)_8, the T_\rm C is about 1.5 K higher than that of the undoped one over the whole pressure range, and reaches 6.4 K at 43 GPa. The upper critical field with field applied along the c axis at typical pressures is about 50\% of the Pauli limit, suggesting a 3D superconductivity. The Hall coefficient in the metallic phase is low and exhibits a peaked behavior at about 30 K, which suggests either a multi-band electronic structure or an electron correlation effect in the system.