Superconductivity induced by external pressure in Eu3−x Sr x Bi2S4F4 (x = 1, 2) compounds

We have studied the temperature-pressure phase diagram of two materials Eu3−x Sr x Bi2S4F4 (x = 1 and x = 2) by electrical resistivity and magnetic measurements down to 2 K. Semiconducting resistive behavior observed in both the materials under ambient conditions transforms into metallic behavior as externally applied pressure gradually increases. Superconductivity is observed in both the materials at and above applied pressure P = 2.37 GPa. Under the highest pressure P ~ 2.9 GPa applied in our measurements, T c is ~9.8 K in Eu2SrBi2S4F4 (x = 1) and 8.2 K in EuSr2Bi2S4F4 (x = 2). Upper critical field H c2(0) ~ 3.04 T (x = 1) and 1.17 T (x = 2) is estimated from magnetic field dependent resistivity measurements at 2.9 GPa. Using the Arrhenius equation, we estimate the thermally activated flux flow activation energy U 0 as 116 K in Eu2SrBi2S4F4 and 39 K in EuSr2Bi2S4F4. At 2 K, DC magnetic susceptibility measurements indicate S-type paramagnetic behavior.