Pressure-Induced Superconducting State of Europium Metal at Low Temperatures

Divalent Eu (4f(7), J=7/2) possesses a strong local magnetic moment which suppresses superconductivity. Under sufficient pressure it is anticipated that Eu will become trivalent (4f(6), J=0) and a weak Van Vleck paramagnet, thus opening the door for a possible superconducting state, in analogy with Am metal (5f(6), J=0) which superconducts at 0.79 K. We present ac susceptibility and electrical resistivity measurements on Eu metal for temperatures 1.5-297 K to pressures as high as 142 GPa. At approximately 80 GPa Eu becomes superconducting at T-c similar or equal to 1.8 K; T-c increases linearly with pressure to 2.75 K at 142 GPa. Eu metal thus becomes the 53rd known elemental superconductor in the periodic table.