Persistent quantum vibronic dynamics in a $5d^1$ double perovskite oxide

TL;DR

This study provides experimental and theoretical evidence of persistent quantum entangled states involving spin, orbital, and lattice degrees of freedom in a 5d^1 double perovskite oxide, revealing complex vibronic dynamics at low temperatures.

Contribution

The paper presents the first direct evidence of orbital-lattice entangled states in a 5d^1 double perovskite, supported by spectroscopic data and theoretical analysis.

Findings

Spectroscopic peaks indicate orbital-lattice entanglement.

Quantum-entangled states persist at low temperatures.

Theoretical models confirm the entangled nature of observed states.

Abstract

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, Ba$_2$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 Ba$_2$CaReO$_6$. Crucially, both theory and experiment demonstrate that these quantum-entangled states persist to low temperatures, despite the onset of multipolar order.