Observation of Quantum Coherence in Mesoscopic Molecular Magnets

By applying a transverse magnetic field B_⊥ of sufficient strength to the uniaxial molecular magnets Fe₈ and Mn₁₂, the tunneling splitting Δₜ of their S0ex0ex=0ex0ex±10 magnetic ground states can be made large compared to perturbations such as hyperfine and dipolar interactions. We present evidence for such a Δₜ from magnetic specific heat data below 1K that is consistent with coherent quantum mechanical tunneling in a ``mesoscopic'' system under such conditions.