Analysis of vibronic coupling in a 4f molecular magnet with FIRMS

For molecular magnets and qubits, coupling between vibrations and electronic spins has a strong influence on spin state lifetime. Here, Kragskow et al present direct measurements of the vibronic transitions in a molecular magnet, showing the critical role of an envelope effect in the spectra. Vibronic coupling, the interaction between molecular vibrations and electronic states, is a fundamental effect that profoundly affects chemical processes. In the case of molecular magnetic materials, vibronic, or spin-phonon, coupling leads to magnetic relaxation, which equates to loss of magnetic memory and loss of phase coherence in molecular magnets and qubits, respectively. The study of vibronic coupling is challenging, and most experimental evidence is indirect. Here we employ far-infrared magnetospectroscopy to directly probe vibronic transitions in [Yb(trensal)] (where H(3)trensal = 2,2,2-tris(salicylideneimino)trimethylamine). We find intense signals near electronic states, which we show arise due to an envelope effect in the vibronic coupling Hamiltonian, which we calculate fully ab initio to simulate the spectra. We subsequently show that vibronic coupling is strongest for vibrational modes that simultaneously distort the first coordination sphere and break the C-3 symmetry of the molecule. With this knowledge, vibrational modes could be identified and engineered to shift their energy towards or away from particular electronic states to alter their impact. Hence, these findings provide new insights towards developing general guidelines for the control of vibronic coupling in molecules.

Automated summary

The coupling between vibrations and electronic spins, known as vibronic coupling, has a significant impact on the spin state lifetime in molecular magnets and qubits. This study presents direct measurements of vibronic transitions in a molecular magnet, highlighting the critical role of an envelope effect in the spectra. The research shows that vibronic coupling is strongest for vibrational modes that distort the first coordination sphere and break the C-3 symmetry of the molecule, providing new insights towards controlling vibronic coupling in molecules.