Quantum entanglement between the spin, orbital, and lattice degrees of freedom in condensed matter systems can emerge due to an interplay between spin-orbit and vibronic interactions. Heavy transition metal ions decorated on a face-centered-cubic lattice, for example, in $5d^1$ double perovskites, are particularly suited to support these quantum entangled states, but direct evidence has not yet been presented. In this work, we report additional peaks in the low-energy spectra of a $5d^1$ double perovskite, ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$, which cannot be explained by adopting a purely classical description of lattice vibrations. Instead, our theoretical analysis demonstrates that these spectroscopic signatures are characteristic of orbital-lattice entangled states in ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$. Crucially, both theory and experiment demonstrate that these quantum-entangled states persist to low temperatures, despite the onset of multipolar order.

Close

PrevNext

View figure in article

• Jahn-Teller effect
• Vibronic effects
• Perovskites
• Transition metal oxides
• Resonant inelastic x-ray scattering
• Vibronic spectroscopy