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

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.

6 pages main text, 4 figures, 8 pages supplementary information

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Cited by in corpus (8)

• Imaging the coherent propagation of collective modes in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ at room temperature
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• Lattice dynamics of the excitonic insulator Ta${}_2$Ni(Se${}_{1-x}$S${}_x$)${}_5$
• A New Era of Excitonic Insulators
• Third-harmonic generation in excitonic insulators
• Field theory for the dynamics of the open $O(N)$ model
• Metastability in Coexisting Competing Orders
• Ab initio Approach to Collective Excitations in Excitonic Insulators