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On Steklov Eigenspaces for Free Boundary Minimal Surfaces in the Unit Ball

We develop new methods to compare the span $\mathcal{C}(Σ)$ of the coordinate functions on a free boundary minimal submanifold $Σ$ embedded in the unit $n$-ball $\mathbb{B}^n$ with its first Steklov eigenspace $\mathcal{E}_{σ_1}(Σ)$. Using these methods, we show that $\mathcal{C}(A)=\mathcal{E}_{σ_1}(A)$ for any embedded free boundary minimal annulus $A$ in $\mathbb{B}^3$ invariant under the antipodal map, and thus prove that $A$ is congruent to the critical catenoid. We also confirm that $\mathcal{C}=\mathcal{E}_{σ_1}$ for any free boundary minimal surface embedded in $\mathbb{B}^3$ with the symmetries of many known or expected examples, including: examples of any positive genus from stacking at least three disks; two infinite families of genus $0$ examples with dihedral symmetry, as well as a finite family with the various Platonic symmetries; and examples of any genus by desingularizing several disks that meet at equal angles along a diameter of the ball.