Spin-forbidden transitions in the molecular nanomagnet V-15

We performed electron spin-resonance measurements on single crystals of the molecular nanomagnet V-15 using a novel broadband spectrometer, both in parallel and in perpendicular modes, we see (B-1 parallel to B-0, B-1 perpendicular to B-0). Measurements were carried out in proximity of the spin level crossing at B-0 = 2.75 T. We observed spin-forbidden transitions from the S = 1/2 zero-field ground state to the S = 3/2 excited state in parallel mode spectra. Spin-forbidden transitions are employed for switching of coherent interactions between qubits in recent quantum simulator proposals. Our theoretical investigations showed that the mixing of spin states can result from either an antisymmetric exchange interaction or a combination of static distortion and hyperfine interaction.