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arXiv · 2012.12912

Signatures of ultrafast reversal of excitonic order in Ta$_2$NiSe$_5$

H. Ning·O. Mehio·M. Buchhold·T. Kurumaji·G. Refael·J. G. Checkelsky·D. Hsieh
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Abstract

In the presence of electron-phonon coupling, an excitonic insulator harbors two degenerate ground states described by an Ising-type order parameter. Starting from a microscopic Hamiltonian, we derive the equations of motion for the Ising order parameter in the phonon coupled excitonic insulator Ta$_2$NiSe$_5$ and show that it can be controllably reversed on ultrashort timescales using appropriate laser pulse sequences. Using a combination of theory and time-resolved optical reflectivity measurements, we report evidence of such order parameter reversal in Ta$_2$NiSe$_5$ based on the anomalous behavior of its coherently excited order-parameter-coupled phonons. Our work expands the field of ultrafast order parameter control beyond spin and charge ordered materials.

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H. Ning, O. Mehio, M. Buchhold, T. Kurumaji, G. Refael, J. G. Checkelsky, D. Hsieh. 2020-12-23. Signatures of ultrafast reversal of excitonic order in Ta$_2$NiSe$_5$. https://doi.org/10.1103/physrevlett.125.267602

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