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

doi:10.1103/PhysRevLett.125.267602

Signatures of Ultrafast Reversal of Excitonic Order in Ta_{2}NiSe_{5}

Phys Rev Lett. 2020 Dec 31;125(26):267602. doi: 10.1103/PhysRevLett.125.267602.

Authors

H Ning^{1

2}, O Mehio^{1

2}, M Buchhold^{1

2}, T Kurumaji³, G Refael^{1

2}, J G Checkelsky³, D Hsieh^{1

2}

Affiliations

¹ Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA.
² Department of Physics, California Institute of Technology, Pasadena, California 91125, USA.
³ Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.

PMID: 33449742
DOI: 10.1103/PhysRevLett.125.267602

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 Letter expands the field of ultrafast order parameter control beyond spin and charge ordered materials.