Properties of the anomalous metallic state in 2D SIT

Characterize the properties of the anomalous metallic state that emerges during the superconductor-to-insulator transition in two-dimensional electronic systems, and ascertain how this state fits within or challenges theories that predict no intermediate metallic phase.

Background

In motivating their study of metallic behavior in diamond, the authors reference a broader unresolved issue in 2D systems: an anomalous metallic state observed between superconducting and insulating phases defies conventional expectations. This state’s properties are not yet well understood and challenge prevailing theoretical frameworks.

By highlighting this open question, the authors position their diamond results within a larger context of unconventional metallic phases in low-dimensional systems, suggesting that insights from diamond may be relevant to understanding this anomalous metallic state.

References

On the other hand, although an anomalous metallic state was observed during the superconductor-to-insulator transition in 2D electronic systems, but its properties are still unclear and poses great challenges to the traditional theories which expect no intermediate metallic phase.

— Superconductivity and metallic behavior in heavily doped bulk single crystal diamond and graphene/diamond heterostructure  (2403.00359 - Lin et al., 2024) in Introduction (opening section)

It is an open question whether this anomalous metal transport is due to the onset of a Bose metal phase, macroscopic quantum tunneling of vortices, spurious heating, emergent spatial inhomogeneity, or some other mechanism.

— Imaging how fluctuations destroy superconductivity in two dimensions  (2609.28837 - Horn et al., 23 Sep 2026) in Section 1, paragraph beginning “The experimental situation is less clear.”