Magnetization Measurement of a Possible High-Temperature Superconducting State in Amorphous Carbon Doped with Sulfur

TL;DR

This study investigates amorphous sulfur-doped carbon, revealing signs of inhomogeneous high-temperature superconductivity around 38 K, with unique magnetic properties and anomalies suggesting a nonstandard superconducting state.

Contribution

The paper reports the discovery of possible high-temperature superconductivity in amorphous sulfur-doped carbon and characterizes its unusual magnetic behavior and phase diagram.

Findings

Superconductivity observed below 38 K in amorphous sulfur-doped carbon.

Anomalous magnetic properties including non-monotonic H_c1(T) and flux lattice melting.

Coexistence of ferromagnetic-like magnetization with superconductivity.

Abstract

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 T_c = 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. In particular, we observed (1) a non-monotonic behavior of the lower critical field H_c1(T); (2) a pronounced positive curvature of the "upper critical field boundary" that we associated with the flux lattice melting line Hm(T); (3) a spontaneous ferromagnetic-like magnetization M0 coexisting with SC. Based on the analysis of experimental results we propose a nonstandard SC state in AC-S.