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Existence and formation mechanism of the quantum metallic phase in diamond

Establish the existence of, and elucidate the formation mechanism for, the quantum metallic phase in diamond, identifying the conditions and microscopic processes that give rise to finite resistivity at low temperatures in heavily doped diamond.

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Background

The authors investigate phase transitions in heavily doped single-crystal diamond and report metallic behavior at low temperatures, contrasting it with the superconducting state. They propose possible mechanisms (loss of pairing amplitude, boson localization potentially involving excitons) but do not provide a definitive explanation.

This explicitly identified unresolved problem concerns both confirming the quantum metallic phase in diamond and understanding how it forms, which is central to interpreting the observed transport phenomena and their relationship to superconductivity.

References

Since the discovery of diamond superconductivity, the existence and formation mechanism of quantum metallic phase in diamond have been an unresolved physical problem.

— Superconductivity and metallic behavior in heavily doped bulk single crystal diamond and graphene/diamond heterostructure (2403.00359 - Lin et al., 1 Mar 2024) in Results and Discussions (paragraph introducing metallic phase, before Fig. 1e–f)