Fig. 4: Superfluid stiffness estimation showing a broadened BKT transition.
a, Integrated dV/dI curves to produce Vintegrated versus Id.c. curves, at different temperatures; these are separate measurements from the switching measurements. The green data points represent the range used for fitting the nonlinear exponent α, corresponding to low current values of around 50 nA. The black dashed lines show linear fits on a log–log scale: log[|Vintegrated|] = αlog[|Id.c.|]. b, Extracted values of the exponent α (green; left axis) and superfluid stiffness Js (blue; right axis) as functions of temperature. The exponents are extracted from the fits in a. The absence of a sharp jump in α indicates a broadened BKT transition. The error bars are calculated as the standard deviation from the fits.
