Identify the superconducting graphite allotrope

Identify the specific graphite allotrope within the magnetically sorted graphite powders that is responsible for the observed above-room-temperature superconductivity, given that only tiny amounts of superconducting material are present in the samples.

Background

The paper reports magnetic-field-based sorting methods (MDS, MVS, MHS) that concentrate superconducting grains from various commercial graphite powders (synthetic, natural, spectroscopically pure). Electrical and magnetic measurements on the concentrates reveal superconducting transitions extending up to approximately 700 K and zero resistance up to roughly 500 K.

Because the superconducting fraction is very small and grains may be only partially superconducting (potentially at interfaces or in twisted multilayers), the authors note that they have not yet been able to identify the precise graphite allotrope responsible for the superconductivity.