Magnetization measurement of a possible high-temperature superconducting state in amorphous carbon doped with sulfur

Magnetization M (T,H) measurements performed on thoroughly characterized commercial amorphous carbon powder doped with sulfur (AC-S), revealed the occurrence of an inhomogeneous superconductivity (SC) below Tc =38 K. The constructed magnetic field-temperature (H-T) phase diagram resembles that of type-II superconductors. However, AC-S demonstrates a number of anomalies, such as: (1) a nonmonotonic behavior of the lower critical-field Hc1 (T); (2) a pronounced positive curvature of the apparent upper critical-field boundary Hc2 (T); and (3) a spontaneous ferromagneticlike magnetization M0 coexisting with SC. Based on the analysis of experimental results we propose a nonstandard SC state in AC-S.