Fig. 2: Bound of the coherence length by quantum metric.
From: Anomalous coherence length in superconductors with quantum metric
a For a conventional superconductor with a dispersive band (as illustrated by the insert) without quantum metric, the coherence length ξ = ℏvF/Δ decreases as Δ (Δ is the superconducting pairing gap) increases and ξ is not bounded from below. b In the presence of quantum metric, the superconducting coherence length ξ has a lower bound of ℓqm. For a superconductor with a narrow band (as illustrated in the insert), the conventional contribution can be suppressed as Δ increases.
