Ultrafast signatures of spin and orbital order in antiferromagnetic $\alpha$-Sr$_2$CrO$_4$

Min-Cheol Lee; Connor Occhialini; Jiarui Li; Zhihai Zhu; Nicholas S. Sirica; La Moyne T. Mix; Dmitry A. Yarotski; Riccardo Comin; Rohit P. Prasankumar

arXiv · 2110.14004

Ultrafast signatures of spin and orbital order in antiferromagnetic $\alpha$-Sr$_2$CrO$_4$

Min-Cheol Lee·Connor Occhialini·Jiarui Li·Zhihai Zhu·Nicholas S. Sirica·La Moyne T. Mix·Dmitry A. Yarotski·Riccardo Comin·Rohit P. Prasankumar

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Abstract

We used femtosecond optical spectroscopy to study ultrafast spin and orbital ordering dynamics in the antiferromagnetic Mott insulator $\alpha$-Sr$_2$CrO$_4$. This chromate system possesses multiple spin and orbital ordered phases, and therefore could enable us to study the unique interplay between these collective phases through their non-equilibrium response to photoexcitation. Here, by varying the pump photon energy, we selectively drove inter-site spin hopping between neighboring Cr $t_{2g}$ orbitals and charge transfer-type transitions between oxygen 2$p$ and Cr $e_{g}$ orbitals. The resulting transient reflectivity dynamics revealed temperature-dependent anomalies across the N${\textrm{\'e}}$el temperature for spin ordering as well as the transition temperatures linked to different types of orbital order. Our results reveal distinct relaxation timescales for spin and orbital orders in $\alpha$-Sr$_2$CrO$_4$ and provide experimental evidence for the phase transition at $T_\textrm{O}$, possibly related to antiferro-type orbital ordering.

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Min-Cheol Lee, Connor Occhialini, Jiarui Li, Zhihai Zhu, Nicholas S. Sirica, La Moyne T. Mix, Dmitry A. Yarotski, Riccardo Comin, Rohit P. Prasankumar. 2021-10-26. Ultrafast signatures of spin and orbital order in antiferromagnetic $\alpha$-Sr$_2$CrO$_4$. https://arxiv.org/abs/2110.14004

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