“…A number of characterizations of the critical catenoid have been obtained by numerous geometers. For example, refer to [10,40,44] for the Morse index estimate, [2,4,7,18,19,24,28,31] for uniqueness results of the critical catenoid, and [5] for a variational characterization in terms of 2-dimensional Hausdorff measure. We should mention that examples of free boundary minimal surfaces in B 3 are very rich.…”