Importance of dynamic lattice effects for crystal field excitations in quantum spin ice candidate Pr${}_2$Zr${}_2$O${}_7$

Abstract

Pr${}_2$Zr${}_2$O${}_7$ is a pyrochlore quantum spin-ice candidate. Using Raman scattering spectroscopy we probe crystal electric field excitations of Pr${}^{3+}$, and demonstrate the importance of their interactions with the lattice. We identify a vibronic interaction with a phonon that leads to a splitting of a doublet crystal field excitation at around 55~meV. We also probe a splitting of the non-Kramers ground state doublet of Pr${}^{3+}$ by observing a double line of the excitations to the first excited singlet state $E_g^0\to A_{1g}$. We show that the splitting has a strong temperature dependence, with the doublet structure most prominent between 50~K and 100~K, and the weight of one of the components strongly decreases on cooling. We suggest a static or dynamic deviation of Pr${}^{3+}$ from the position in the ideal crystal structure can be the origin of the effect, with the deviation strongly decreasing at low temperatures.

arXiv comment6 pages, 3 figures

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• Phonon spectrum of Pr${}_2$Zr${}_2$O${}_7$ and Pr${}_2$Ir${}_2$O${}_7$ as an evidence of coupling of the lattice with electronic and magnetic degrees of freedom
• Two-Peak Heat Capacity Accounts for $R\ln (2)$ Entropy and Ground State Access in the Dipole-Octupole Pyrochlore Ce${}_2$Hf${}_2$O${}_7$
• Probing emergent QED in quantum spin ice via Raman scattering of phonons: shallow inelastic scattering and pair production