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arXiv · 2308.03237

Strong coupling of lattice and orbital excitations in quantum magnet Ca$_{10}$Cr$_7$O$_{28}$: Anomalous temperature dependence of Raman phonons

Srishti Pal·Arnab Seth·Anzar Ali·Yogesh Singh·D. V. S. Muthu·Subhro Bhattacharjee·A. K. Sood
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Abstract

We report low-temperature Raman signatures of the Heisenberg quantum magnet Ca$_{10}$Cr$_7$O$_{28}$, showing clear anomalies in phonon mode frequencies and linewidths below $\sim$100 K. This crossover temperature lies in between the Jahn-Teller (JT) temperature scale ($>$ room temperature) and the temperature scale associated with the spin exchange interactions ($<$ 12 K). Our experimental observation is well captured by a novel secondary JT transition associated with a cooperative reorientation of the orbitals giving rise to anomalies in the temperature dependence of Raman frequencies and linewidths. Such orbital reorganisation, in turn, affects the spin-spin exchange interactions that decide the fate of the magnet at lower temperatures and hence provide important clues to understand the energetics of the possible lower temperature quantum paramagnetic phase.

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Srishti Pal, Arnab Seth, Anzar Ali, Yogesh Singh, D. V. S. Muthu, Subhro Bhattacharjee, A. K. Sood. 2023-08-07. Strong coupling of lattice and orbital excitations in quantum magnet Ca$_{10}$Cr$_7$O$_{28}$: Anomalous temperature dependence of Raman phonons. https://doi.org/10.1103/physrevb.108.l241103

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