Coherent order parameter oscillations in the ground state of the excitonic insulator Ta
            <sub>2</sub>
            NiSe
            <sub>5</sub>

Werdehausen, Daniel; Takayama, T.; Höppner, M.; Albrecht, Gelon; Rost, Andreas W.; Lu, Yangfan; Manske, Dirk; Takagi, H.; Kaiser, Stefan

doi:10.1126/sciadv.aap8652

Cited by 143 publications

(158 citation statements)

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“…While these initiatives are underway, our technique may also serve as a probe for non-equilibrium superconductivity 33,34 . With so many interesting prospects, we see a bright future for phase-resolved spectroscopy of collective modes in superconductors and beyond [35][36][37][38] . Fig.…”

Section: Discussionmentioning

confidence: 99%

Phase-resolved Higgs response in superconducting cuprates

et al. 2020

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In high-energy physics, the Higgs field couples to gauge bosons and fermions and gives mass to their elementary excitations. Experimentally, such couplings can be inferred from the decay product of the Higgs boson, i.e., the scalar (amplitude) excitation of the Higgs field. In superconductors, Cooper pairs bear a close analogy to the Higgs field. Interaction between the Cooper pairs and other degrees of freedom provides dissipation channels for the amplitude mode, which may reveal important information about the microscopic pairing mechanism. To this end, we investigate the Higgs (amplitude) mode of several cuprate thin films using phase-resolved terahertz third harmonic generation (THG). In addition to the heavily damped Higgs mode itself, we observe a universal jump in the phase of the driven Higgs oscillation as well as a non-vanishing THG above T c. These findings indicate coupling of the Higgs mode to other collective modes and potentially a nonzero pairing amplitude above T c .

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Section: Discussionmentioning

confidence: 99%

Phase-resolved Higgs response in superconducting cuprates

et al. 2020

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“…Originally discussed in the context of particle physics [2] and superconductivity [3], Higgs and Goldstone excitations were found in cold atom systems, such as superfluids [4][5][6][7][8] or supersolids [9]. Higgs and Goldstone modes are well-studied in superconductors today [10][11][12][13][14][15][16][17][18][19][20][21], and similar manifestations have recently been reported in charge density wave (CDW) systems [22][23][24], antiferromagnets [25][26][27], and excitonic insulators [28]. It has been debated whether the optical and acoustic vibrational modes of solids can be considered Higgs and Goldstone excitations of the crystal lattice [29].…”

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Parametric Excitation of an Optically Silent Goldstone-Like Phonon Mode

2020

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It has recently been indicated that the hexagonal manganites exhibit Higgs-and Goldstone-like phonon modes that modulate the amplitude and phase of their primary order parameter. Here, we describe a mechanism by which a silent Goldstone-like phonon mode can be coherently excited, which is based on nonlinear coupling to an infrared-active Higgs-like phonon mode. Using a combination of first-principles calculations and phenomenological modeling, we describe the coupled Higgs-Goldstone dynamics in response to the excitation with a terahertz pulse. Besides theoretically demonstrating coherent control of crystallographic Higgs and Goldstone excitations, we show that the previously inaccessible silent phonon modes can be excited coherently with this mechanism.Order parameters are physical observables that are used to quantify the different states of matter. Their amplitudes and phases can be excited by external stimuli, such as a laser pulse, leading to exotic states of matter that cannot be accessed in equilibrium [1]. Two particular excitations are Higgs and Goldstone modes, which correspond to the modulation of the amplitude and phase of an order parameter that breaks a continuous symmetry. Originally discussed in the context of particle physics [2] and superconductivity [3], Higgs and Goldstone excitations were found in cold atom systems, such as superfluids [4][5][6][7][8] or supersolids [9]. Higgs and Goldstone modes are well-studied in superconductors today [10][11][12][13][14][15][16][17][18][19][20][21], and similar manifestations have recently been reported in charge density wave (CDW) systems [22][23][24], antiferromagnets [25][26][27], and excitonic insulators [28]. It has been debated whether the optical and acoustic vibrational modes of solids can be considered Higgs and Goldstone excitations of the crystal lattice [29]. Several complex transition metal oxide compounds have shown signatures of optical Goldstone-like phonon modes that live in their symmetry-broken potential energy landscape [30][31][32][33][34].Coherent control over Raman-active phonons via impulsive stimulated Raman scattering using visible light pulses is well-established [35,36]. Recently, the excitation of infrared (IR)-active phonons with large amplitudes via IR absorption has become feasible through the development of high intensity terahertz and mid-IR sources. This progress has enabled selective control over the dynamics of the crystal lattice through nonlinear phonon interactions using ionic Raman scattering [37-39] and two-particle absorption mechanisms [40][41][42][43][44][45]. In contrast, phonon modes that do not respond to IR absorption or Raman scattering techniques, so called silent modes, can only be detected through hyper-Raman scattering. As hyper-Raman scattering is a third-order interaction of the electric field component of light with a * djuraschek@seas.harvard.edu † prineha@seas.harvard.edu phonon mode, it is inefficient and no coherent excitation has been achieved yet. Higgs and Goldstone modes, similar to silent p...

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“…4 For the present study, we have performed the measurements of time-and angleresolved photoemission spectroscopy (TARPES) to obtain such evidence that Ta2NiSe5 is actually an excitonic insulator from its pump-fluence dependence of the photoexcitation dynamics. Whereas several time-resolved studies on Ta2NiSe5 have been reported so far [14][15][16][17] , the present study is quite unique in that we employ a pump laser with shorter pulse duration (~ 30 fs), and extreme ultra violet (XUV) laser from high harmonic generation for probe pulses. Whereas we have employed 1 kHz for the repetition rate of the laser in order to generate higher order harmonics, this makes higher pump fluence available compared to higher repetition rate with the same average power of pump pulses.…”

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Photo-induced semimetallic states realised in electron–hole coupled insulators

et al. 2018

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Using light to manipulate materials into desired states is one of the goals in condensed matter physics, since light control can provide ultrafast and environmentally friendly photonics devices. However, it is generally difficult to realise a photo-induced phase which is not merely a higher entropy phase corresponding to a high-temperature phase at equilibrium. Here, we report realisation of photo-induced insulator-to-metal transitions in Ta2Ni(Se1−xSx)5 including the excitonic insulator phase using time- and angle-resolved photoemission spectroscopy. From the dynamic properties of the system, we determine that screening of excitonic correlations plays a key role in the timescale of the transition to the metallic phase, which supports the existence of an excitonic insulator phase at equilibrium. The non-equilibrium metallic state observed unexpectedly in the direct-gap excitonic insulator opens up a new avenue to optical band engineering in electron–hole coupled systems.

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Coherent order parameter oscillations in the ground state of the excitonic insulator Ta ₂ NiSe ₅

Abstract: Ultrafast spectroscopy reveals coherent oscillations of a phonon-coupled BEC of excitons in an excitonic insulator.

Cited by 143 publications

References 44 publications

Phase-resolved Higgs response in superconducting cuprates

Phase-resolved Higgs response in superconducting cuprates

Parametric Excitation of an Optically Silent Goldstone-Like Phonon Mode

Photo-induced semimetallic states realised in electron–hole coupled insulators

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Coherent order parameter oscillations in the ground state of the excitonic insulator Ta 2 NiSe 5

Abstract: Ultrafast spectroscopy reveals coherent oscillations of a phonon-coupled BEC of excitons in an excitonic insulator.

Cited by 143 publications

References 44 publications

Phase-resolved Higgs response in superconducting cuprates

Phase-resolved Higgs response in superconducting cuprates

Parametric Excitation of an Optically Silent Goldstone-Like Phonon Mode

Photo-induced semimetallic states realised in electron–hole coupled insulators

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Product

Resources

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Coherent order parameter oscillations in the ground state of the excitonic insulator Ta ₂ NiSe ₅