Light-induced collective pseudospin precession resonating with Higgs mode in a superconductor

Matsunaga, Ryusuke; Tsuji, Naoto; Fujita, Hiroyuki; Sugioka, Arata; Makise, Kazumasa; Uzawa, Yoshinori; Terai, Hirotaka; Wang, Zhen; Aoki, Hideo; Shimano, Ryo

doi:10.1126/science.1254697

Cited by 472 publications

(634 citation statements)

References 30 publications

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“…4d), including the recent observation of the Higgs mode 86 in a disordered superconductor and in NbN using time-resolved terarhertz spectroscopy 87 .…”

Section: Nature Materials Doi: 101038/nmat5017mentioning

confidence: 99%

Towards properties on demand in quantum materials

2017

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Q uantum materials are on the ascent. This term embodies a vast portfolio of compounds and phenomena where ramifications of quantum mechanics are demonstrably real. Quantum materials are in the vanguard of contemporary physics in part because these systems afford an exceptional venue to uncover the many roles of symmetry, topology, dimensionality and strong correlations in macroscopic observables. Here we set out to explore the ways and means of creating new states of matter in quantum materials and manipulating their phases via external stimuli. Practical control of these properties is a precondition for exploiting quantum advantages in new photonic, electronic and energy technologies, a task of significant societal impact 1 . We will primarily focus on the following classes of quantum materials: transition metal oxides, Fe-and Cu-based high-T c superconductors, van der Waals semiconductors, topological insulators and Weyl semimetals, and, finally, graphene.The properties of quantum materials are anomalously sensitive to external stimuli. In these systems, interactions associated with spin, charge, lattice and orbital degrees of freedom are commonly on par with the electronic kinetic energy. A rather fragile balance between coexisting and competing ground states can be readily shifted via external stimuli, leading to a raft of quantum phases and transitions between them 2,3 . Furthermore, certain classes of driven quantum states (Fig. 1a and Box 1) are explicit products of coherent interaction between light and matter 4-6 . Alternatively, the properties of quantum materials can be pre-programmed by directly manipulating the electronic wavefunction and the attendant Berry phase that give rise to the anomalous velocity of electrons in a solid [7][8][9] . These complementary avenues of controls mean that investigations no longer need to be reduced to merely observing (in contrast, for example, to astrophysics). Instead, it is now feasible to attain, in a predictable fashion, 'properties on demand' by steering a quantum material towards a desirable ground, metastable or transient state. The past decade has witnessed an explosion in the field of quantum materials, headlined by the predictions and discoveries of novel Landau-symmetry-broken phases in correlated electron systems, topological phases in systems with strong spin-orbit coupling, and ultra-manipulable materials platforms based on two-dimensional van der Waals crystals. Discovering pathways to experimentally realize quantum phases of matter and exert control over their properties is a central goal of modern condensed-matter physics, which holds promise for a new generation of electronic/photonic devices with currently inaccessible and likely unimaginable functionalities. In this Review, we describe emerging strategies for selectively perturbing microscopic interaction parameters, which can be used to transform materials into a desired quantum state. Particular emphasis will be placed on recent successes to tailor electronic interaction parameters through th...

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“…4d), including the recent observation of the Higgs mode 86 in a disordered superconductor and in NbN using time-resolved terarhertz spectroscopy 87 .…”

Section: Nature Materials Doi: 101038/nmat5017mentioning

confidence: 99%

Towards properties on demand in quantum materials

2017

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“…Matsunaga et al [25,26] directly measured the timedependent amplitude | (t)| induced by an ultrafast electromagnetic perturbation in Nb 1-x Ti x N films using terahertzpump-terahertz-probe spectroscopy. The underlying system is a BCS superconductor [weak-coupling regime of the onechannel model (1.3)] and for perturbation strength below certain threshold its nonadiabatic dynamics falls within region II of our quench phase diagrams.…”

Section: Experimental Signaturesmentioning

confidence: 99%

Quantum quench phase diagrams of ans-wave BCS-BEC condensate

et al. 2015

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We study the dynamic response of an s-wave BCS-BEC (atomic-molecular) condensate to detuning quenches within the two-channel model beyond the weak-coupling BCS limit. At long times after the quench, the condensate ends up in one of three main asymptotic states (nonequilibrium phases), which are qualitatively similar to those in other fermionic condensates defined by a global complex order parameter. In phase I the amplitude of the order parameter vanishes as a power law, in phase II it goes to a nonzero constant, and in phase III it oscillates persistently. We construct exact quench phase diagrams that predict the asymptotic state (including the many-body wave function) depending on the initial and final detunings and on the Feshbach resonance width. Outside of the weak-coupling regime, both the mechanism and the time dependence of the relaxation of the amplitude of the order parameter in phases I and II are modified. Also, quenches from arbitrarily weak initial to sufficiently strong final coupling do not produce persistent oscillations in contrast to the behavior in the BCS regime. The most remarkable feature of coherent condensate dynamics in various fermion superfluids is an effective reduction in the number of dynamic degrees of freedom as the evolution time goes to infinity. As a result, the long-time dynamics can be fully described in terms of just a few new collective dynamical variables governed by the same Hamiltonian only with "renormalized" parameters. Combining this feature with the integrability of the underlying (e.g., the two-channel) model, we develop and consistently present a general method that explicitly obtains the exact asymptotic state of the system.

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“…For example, as the electron momentum is varied between −k x and +k x , there is an increase and then decrease in the scattering intensity as recorded by Tr-ARPES. As discussed above, equation (2) implies that for electron momentum along the light polarization direction (that is, along k x ), the photoemitted intensity can be written as ∝J n (β ∓ α) 2 for ±k x . Thus, by varying the electron momentum, we can control the scattering between Floquet-Bloch and Volkov states.…”

mentioning

confidence: 99%

“…Moreover, by controlling the light polarization we can negate Volkov states to generate pure Floquet-Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light-matter interaction.The manipulation of solids using ultrafast optical pulses has opened up a new paradigm in condensed matter physics by allowing the study of emergent physical properties that are otherwise inaccessible in equilibrium 1,2,10 . An important example is provided by the Floquet-Bloch states 11 , which emerge in solids owing to a coherent interaction between Bloch states inside the solid and a periodic driving potential.…”

mentioning

confidence: 99%

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Selective scattering between Floquet–Bloch and Volkov states in a topological insulator

Mahmood¹,

Chan²,

Alpichshev³

et al. 2016

Nature Phys

336

273

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The coherent optical manipulation of solids is emerging as a promising way to engineer novel quantum states of matter 1-5 . The strong time-periodic potential of intense laser light can be used to generate hybrid photon-electron states. Interaction of light with Bloch states leads to Floquet-Bloch states, which are essential in realizing new photo-induced quantum phases [6][7][8] . Similarly, dressing of free-electron states near the surface of a solid generates Volkov states, which are used to study nonlinear optics in atoms and semiconductors 9 . The interaction of these two dynamic states with each other remains an open experimental problem. Here we use time-and angle-resolved photoemission spectroscopy (Tr-ARPES) to selectively study the transition between these two states on the surface of the topological insulator Bi 2 Se 3 . We find that the coupling between the two strongly depends on the electron momentum, providing a route to enhance or inhibit it. Moreover, by controlling the light polarization we can negate Volkov states to generate pure Floquet-Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light-matter interaction.The manipulation of solids using ultrafast optical pulses has opened up a new paradigm in condensed matter physics by allowing the study of emergent physical properties that are otherwise inaccessible in equilibrium 1,2,10 . An important example is provided by the Floquet-Bloch states 11 , which emerge in solids owing to a coherent interaction between Bloch states inside the solid and a periodic driving potential. This is a consequence of the Floquet theorem 12 , which states that a Hamiltonian periodic in time with period T has eigenstates that are evenly spaced by the drive energy (2π/T ). Floquet-Bloch states have generated a lot of interest recently both for realizing exotic states of matter such as a Floquet Chern insulator 7 , as well as understanding non-equilibrium periodic thermodynamics 13,14 . Experimental observation of these states requires the measurement of the transient electronic band structure of a crystal as it is perturbed by light. As has recently been demonstrated 15 in the topological insulator Bi 2 Se 3 , time-and angleresolved photoemission spectroscopy (Tr-ARPES) is a key tool that can achieve this. Characteristic signatures of Floquet-Bloch states in the Tr-ARPES spectra include replicas of the original band structure that are separated by the driving photon energy 15 .In addition to Floquet-Bloch states, light can also generate other coherent phenomena in solids [16][17][18] . In particular, it can dress freeelectron states near the surface of a solid (Fig. 1a), as the surface can provide the momentum conservation necessary for a photon to interact with a free electron. This dressing was first observed in time-resolved photoemission experiments 17 and has subsequently been referred to as laser-assisted photoemission (LAPE). LAPE is typically understood [19][20][21] by invoking the Volkov solution, which is an e...

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Light-induced collective pseudospin precession resonating with Higgs mode in a superconductor

Cited by 472 publications

References 30 publications

Towards properties on demand in quantum materials

Towards properties on demand in quantum materials

Quantum quench phase diagrams of ans-wave BCS-BEC condensate

Selective scattering between Floquet–Bloch and Volkov states in a topological insulator

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