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arXiv · 1801.05439

Evidence of an improper displacive phase transition in Cd$_2$Re$_2$O$_7$ via time-resolved coherent phonon spectroscopy

J. W. Harter·D. M. Kennes·H. Chu·A. de la Torre·Z. Y. Zhao·J. -Q. Yan·D. G. Mandrus·A. J. Millis·D. Hsieh
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Abstract

We have used a combination of ultrafast coherent phonon spectroscopy, ultrafast thermometry, and time-dependent Landau theory to study the inversion symmetry breaking phase transition at $T_c = 200$ K in the strongly spin-orbit coupled correlated metal Cd$_2$Re$_2$O$_7$. We establish that the structural distortion at $T_c$ is a secondary effect through the absence of any softening of its associated phonon mode, which supports a purely electronically driven mechanism. However, the phonon lifetime exhibits an anomalously strong temperature dependence that decreases linearly to zero near $T_c$. We show that this behavior naturally explains the spurious appearance of phonon softening in previous Raman spectroscopy experiments and should be a prevalent feature of correlated electron systems with linearly coupled order parameters.

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J. W. Harter, D. M. Kennes, H. Chu, A. de la Torre, Z. Y. Zhao, J. -Q. Yan, D. G. Mandrus, A. J. Millis, D. Hsieh. 2018-01-16. Evidence of an improper displacive phase transition in Cd$_2$Re$_2$O$_7$ via time-resolved coherent phonon spectroscopy. https://doi.org/10.1103/physrevlett.120.047601

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