3 years ago

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

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

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.

Publisher URL: http://arxiv.org/abs/1801.05439

DOI: arXiv:1801.05439v1

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