Mechanism of ground-state selection in the frustrated molecular spin cluster V15

We report an inelastic neutron scattering (INS) study under a magnetic field on the frustrated molecular spin cluster V-15. Several field-dependent transitions are observed and provide a comprehensive understanding of the low-energy quantum spin states. The energy gap 2Delta(o) approximate to 27(3) mueV between the two lowest S = 1/2 Kramers doublets is unambiguously attributed to a symmetry lowering of the cluster. The INS data are mapped onto an S = 1/2 Antiferromagnetic Heisenberg triangle with scalene distortion. A quantitative description of the wave function mixing within the ground state is derived.