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 H3trensal = 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 C3 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.
Vibrations play a prominent role
in magnetic relaxation processes
of molecular spin qubits as they couple to spin states, leading to
the loss of quantum information. Direct experimental determination
of vibronic coupling is crucial to understand and control the spin
dynamics of these nano-objects, which represent the limit of miniaturization
for quantum devices. Herein, we measure the magneto-infrared properties
of the molecular spin qubit system Na9[Ho(W5O18)2]·35H2O. Our results place
significant constraints on the pattern of crystal field levels and
the vibrational excitations allowing us to unravel vibronic decoherence
pathways in this system. We observe field-induced spectral changes
near 63 and 370 cm–1 that are modeled in terms of
odd-symmetry vibrations mixed with f-manifold crystal
field excitations. The overall extent of vibronic coupling in Na9[Ho(W5O18)2]·35H2O is limited by a modest coupling constant (on the order of
0.25) and a transparency window in the phonon density of states that
acts to keep the intramolecular vibrations and M
J levels apart. These findings advance the understanding of
vibronic coupling in a molecular magnet with atomic clock transitions
and suggest strategies for designing molecular spin qubits with improved
coherence lifetimes.
We report the physicochemical characteristics of novel Co-based pyrrolidinium analogs: (C4H10N)2CoCl4 (PCC) and (C4H10N)2CoBr4 (PCB). Both compounds consist of the zero-dimensional (OD) anionic network and disordered pyrolidinium cations. The structural...
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