G. Alessandrini et R. Magnanini, SYMMETRY AND NONSYMMETRY FOR THE OVERDETERMINED STEKLOFF EIGENVALUE PROBLEM, Zeitschrift fur angewandte Mathematik und Physik, 45(1), 1994, pp. 44-52
We consider the Stekloff eigenvalue problem (1.1)-(1.2); Payne and Phi
lippin conjectured that if u is an eigenfunction which satisfies the o
verdetermined condition \($) over bar Vu\ = 1 on partial derivative Om
ega, then Omega should be a disk. In this paper we show that this conj
ecture holds if and only if the complex potential F associated to u va
nishes only at one point. Then we show how to construct non-symmetric
domains in the case where F vanishes at more than one point.