Signatures of Ultrafast Reversal of Excitonic Order in 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>Ta</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mi>NiSe</mml:mi></mml:mrow><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Ning, Honglie; Mehio, Omar; Buchhold, Michael; Kurumaji, Takashi; Refael, Gil; Checkelsky, Joseph; Hsieh, David

doi:10.1103/physrevlett.125.267602

Cited by 19 publications

(12 citation statements)

References 57 publications

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“…Among this family of materials, particular attention has been devoted to Ta 2 NiSe 5 following hints of the potential existence of an EI phase below 328 K (8)(9)(10)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). These works have provided insights into the properties in Ta 2 NiSe 5 , for instance, by using equilibrium (8,12) and time-resolved (9,17,18,21,23) angle-resolved photoemission spectroscopy (ARPES), by analyzing the effect of physical and chemical pressure (14,22), by doping (16), and by detecting anomalies in charge transport (14), optical signatures (24,25), and phonon properties (10,15,19,20,22,26) as a function of temperature.…”

Section: Introductionmentioning

confidence: 99%

Imaging the coherent propagation of collective modes in the excitonic insulator Ta ₂ NiSe ₅ at room temperature

et al. 2021

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Excitonic insulators host a condensate of electron-hole pairs at equilibrium, giving rise to collective many-body effects. Although several materials have emerged as excitonic insulator candidates, evidence of long-range coherence is lacking and the origin of the ordered phase in these systems remains controversial. Here, using ultrafast pump-probe microscopy, we investigate the possible excitonic insulator Ta2NiSe5. Below 328 K, we observe the anomalous micrometer-scale propagation of coherent modes at velocities of ~105 m/s, which we attribute to the hybridization between phonon modes and the phase mode of the condensate. We develop a theoretical framework to support this explanation and propose that electronic interactions provide a substantial contribution to the ordered phase in Ta2NiSe5. These results allow us to understand how the condensate’s collective modes transport energy and interact with other degrees of freedom. Our study provides a unique paradigm for the investigation and manipulation of these properties in strongly correlated materials.

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Section: Introductionmentioning

confidence: 99%

Imaging the coherent propagation of collective modes in the excitonic insulator Ta ₂ NiSe ₅ at room temperature

et al. 2021

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“…This amplitude saturation as a function of fluence is one of the signatures of order inversion to look for in CDWs but also in other systems with degenerate ground states such as excitonic insulators, as recently demonstrated in Ref. 33.…”

Section: Resultsmentioning

confidence: 60%

Theoretical description of time-resolved photoemission in charge-density-wave materials out to long times

Petrović¹,

Weber²,

Freericks³

2022

Preprint

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We describe coupled electron-phonon systems semiclassically-Ehrenfest dynamics for the phonons and quantum mechanics for the electrons-using a classical Monte Carlo approach that determines the nonequilibrium response to a large pump field. The semiclassical approach is quite accurate, because the phonons are excited to average energies much higher than the phonon frequency, eliminating the need for a quantum description. The numerical efficiency of this method allows us to perform a self-consistent time evolution out to very long times (tens of picoseconds) enabling us to model pump-probe experiments of a charge density wave (CDW) material. Our system is a half-filled, one-dimensional (1D) Holstein chain that exhibits CDW ordering due to a Peierls transition. The chain is subjected to a time-dependent electromagnetic pump field that excites it out of equilibrium, and then a second probe pulse is applied after a time delay. By evolving the system to long times, we capture the complete process of lattice excitation and subsequent relaxation to a new equilibrium, due to an exchange of energy between the electrons and the lattice, leading to lattice relaxation at finite temperatures. We employ an indirect (impulsive) driving mechanism of the lattice by the pump pulse due to the driving of the electrons by the pump field. We identify two driving regimes, where the pump can either cause small perturbations or completely invert the initial CDW order. Our work successfully describes the ringing of the amplitude mode in CDW systems that has long been seen in experiment, but never successfully explained by microscopic theory.

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“…IV). This may have already been observed in a recent experiment [30]. From the interband hybridization ∆ p ≈ 36 meV and the chain width d ≈ 5 Å, we estimate the threshold field to be In this section, we show the detailed derivation of the effective low energy Lagrangian (Eq.…”

Section: The Mean Field Hamiltonianmentioning

confidence: 53%

“…In all cases the excitonic order parameter may be 'steered' by applied interlayer/chain electric fields via the AC Josephson effect, enabling controlled switching of degenerate ground states. This order parameter steering applies as well to the EI candidate Ta 2 NiSe 5 [22,[26][27][28][29][30].…”

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confidence: 99%

Second order Josephson effect in excitonic insulators

Sun,

Kaneko,

Golež

et al. 2021

Preprint

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We show that in electron-hole bilayers with excitonic order arising from conduction and valence bands formed by atomic orbitals that transform differently under inversion, nonzero interlayer tunneling leads to a second order Josephson effect. This means the interlayer electrical current is related to the phase of the excitonic order parameter as J = Jc sin 2θ instead of J = Jc sin θ, and that the system has two degenerate ground states that can be switched by an interlayer voltage. In a three dimensional stack of alternating electron-hole planes or a two dimensional stack of chains, the second order Josephson coupling can lead to a Weyl semimetal or a quantum anomalous hall insulator, respectively. A generic order parameter steering effect is demonstrated, whereby electric field pulses perpendicular to the layers and chains can steer the order parameter phase between the two degenerate ground states. The steering is also applicable to the excitonic insulator candidate Ta2NiSe5.

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Signatures of Ultrafast Reversal of Excitonic Order in Ta2NiSe5

Cited by 19 publications

References 57 publications

Imaging the coherent propagation of collective modes in the excitonic insulator Ta ₂ NiSe ₅ at room temperature

Imaging the coherent propagation of collective modes in the excitonic insulator Ta ₂ NiSe ₅ at room temperature

Theoretical description of time-resolved photoemission in charge-density-wave materials out to long times

Second order Josephson effect in excitonic insulators

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Signatures of Ultrafast Reversal of Excitonic Order in Ta2NiSe5

Cited by 19 publications

References 57 publications

Imaging the coherent propagation of collective modes in the excitonic insulator Ta 2 NiSe 5 at room temperature

Imaging the coherent propagation of collective modes in the excitonic insulator Ta 2 NiSe 5 at room temperature

Theoretical description of time-resolved photoemission in charge-density-wave materials out to long times

Second order Josephson effect in excitonic insulators

Contact Info

Product

Resources

About

Imaging the coherent propagation of collective modes in the excitonic insulator Ta ₂ NiSe ₅ at room temperature

Imaging the coherent propagation of collective modes in the excitonic insulator Ta ₂ NiSe ₅ at room temperature