Lightwave-driven gapless superconductivity and forbidden quantum beats by terahertz symmetry breaking

Yang, Xu; Vaswani, Chirag; Sundahl, C.; Mootz, M.; Luo, Liang; Kang, Jong Hon; Perakis, I. E.; Eom, Chang‐Beom; Wang, J.

doi:10.1038/s41566-019-0470-y

Cited by 120 publications

(157 citation statements)

References 31 publications

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“…As a consequence, for broadband pulses the spectral components of δE probe (t pp ) are dominated by the characteristic frequency of the mode, ω osc = ω res , while for narrowband pulses δE probe (t pp ) oscillates at twice the pump frequency, ω osc = 2Ω pump , with an amplitude K(2Ω pump ) maximized when 2Ω pump = ω res . These expectations match rather well the observations reported so far in several SC systems [4][5][6][7][8] . From the theoretical point of view, establishing such a general paradigm provides also a scheme for further theoretical investigations aimed at linking the experimental observations to the properties of the underlying microscopic model.…”

supporting

confidence: 92%

“…While the frequency of the SC oscillations is well captured by the parabolic-band approximation (35) for the non-linear kernel, their long-time decay depends crucially on the band-structure details. This can be again understood by relying on the general equation (8) for the transmitted probe field. In the case of a broadband pulse, and setting for simplicity t g = 0, we can safely approximate the long-time behavior of δE probe (t pp ) with the time dependence on the non-linear kernel K(t):…”

Section: Pump-probe Spectroscopy Of Superconducting Modesmentioning

confidence: 99%

“…The present work aims at filling in part this knowl- * mattia.udina@uniroma1.it † tommaso.cea@imdea.org ‡ lara.benfatto@roma1.infn.it edge gap by providing a general theoretical scheme to understand the origin of time-resolved oscillations observed in typical TH pump-THz/eV probe measurements. This experimental technique has been successfully applied in the last years to investigate the properties of both conventional superconducting (SC) compounds [4][5][6][7][8][9] , whose spectral gap ∆ lies in the THz region, and layered superconductors 10,11 with an interlayer Josephson plasma frequency again in the THz range. The general scheme consists in probing the effects of the intense THz pulse by measuring the pump-induced changes δE probe (t pp ) in the transmitted (for a thin film) or reflected (for a bulk crystal) probe field at a fixed observation time, as a function of the pump-probe delay t pp .…”

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confidence: 99%

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Theory of coherent-oscillations generation in terahertz pump-probe spectroscopy: From phonons to electronic collective modes

2019

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Time-resolved spectroscopies using intense THz pulses appear as a promising tool to address collective electronic excitations in condensed matter. In particular recent experiments showed the possibility to selectively excite collective modes emerging across a phase transition, as it is the case for superconducting and charge-density-wave (CDW) systems. One possible signature of these excitations is the emergence of coherent oscillations of the differential probe field in pump-probe protocols. While the analogy with the case of phonon modes suggests that the basic underlying mechanism should be a sum-frequency stimulated Raman process, a general theoretical scheme able to describe the experiments and to define the relevant optical quantity is still lacking. Here we provide this scheme by showing that coherent oscillations as a function of the pump-probe time delay can be linked to the convolution in the frequency domain between the squared pump field and a Raman-like non-linear optical kernel. This approach is applied and discussed in few paradigmatic examples: ordinary phonons in an insulator, and collective charge and Higgs fluctuations across a superconducting and a CDW transition. Our results not only account very well for the existing experimental data in a wide variety of systems, but they also offer an useful perspective to design future experiments in emerging materials.In the last decade, a significant advance in the investigation of complex systems has been gained thanks to the huge experimental progress in time-resolved spectroscopic techniques 1,2 . On very general grounds, the basic idea behind any pump-probe protocol is to first excite the system with a short and very intense electromagnetic pulse (pump), and then to monitor its relaxation towards equilibrium by using a secondary, weak pulse (probe) applied with a finite time delay with respect to the pump. This general protocol can then be implemented in several different ways, according to the nature of the spectroscopic measurement (angle-resolved photoemission, optical reflection or transmission, etc.) or to the wavelength of the pump/probe fields. However, in all cases one has to face with two phenomena which mark the difference with respect to ordinary equilibrium spectroscopies: (i) the use of an intense pulse triggers in general non-linear optical processes; (ii) the subsequent relaxation encodes by definition non-equilibrium phenomena on time scales which depend on the characteristics of the experiment and of the system under investigation. Due in part to these innovative aspects, many pump-probe protocols still lack a general theoretical framework able to connect the measured quantities to the material properties. More specifically, while Kubo linear-response theory 3 represents nowadays the standard theoretical tool needed to compute the optical response of any system to a weak external perturbation, an analogous protocol for timeresolved spectroscopies has not been established yet.The present work aims at filling in part this knowl- * mat...

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confidence: 92%

Section: Pump-probe Spectroscopy Of Superconducting Modesmentioning

confidence: 99%

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confidence: 99%

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Theory of coherent-oscillations generation in terahertz pump-probe spectroscopy: From phonons to electronic collective modes

2019

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“…Such THz photon driven coherence mechanism complements the spontaneous symmetry protection mechanism in the ground state. However, its observation requires intense THz pump and THz conductivity probe spectroscopy measurements [18][19][20][21][22] of the coherent phonon-dressed TPS, which has never been demonstrated so far.…”

Section: Introductionmentioning

confidence: 99%

Light control of surface–bulk coupling by terahertz vibrational coherence in a topological insulator

et al. 2020

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The demand for disorder-tolerant quantum logic and spin electronics can be met by generating and controlling dissipationless spin currents protected by topology. Dirac fermions with helical spin-locking surface transport offer a way of achieving such a goal. Yet, surface-bulk coupling can lead to strong Dirac electron scattering with bulk carriers and phonons as well as impurities, assisted by such dissipative channel, which results in "topological breakdown". Here, we demonstrate that coherent lattice vibrations periodically driven by a single-cycle terahertz (THz) pulse can significantly suppress such dissipative channel in topological insulators. This is achieved by reducing the phase space in the bulk available for Dirac fermion scattering into during coherent lattice oscillations in Bi 2 Se 3 . This light-induced suppression manifests as a remarkable transition exclusively in surface transport, absent for bulk, above the THz electric fields for driving coherent phonons, which prolongs the surface transport lifetime. These results, together with simulations, identify the critical role of spin-orbit coupling for the "phase space contraction" mechanism that suppresses the surface-bulk coupling. Imposing vibrational quantum coherence into topological states of matter may become a universal light control principle for reinforcing the symmetry-protected helical transport.npj Quantum Materials (2020) 5:13 ; https://doi.

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“…Specifically, free oscillations of the Higgs mode, with its characteristic frequency of 2Δ, can be launched by an ultrashort terahertz pulse quenching the free energy of the order parameter 9 . Alternatively, it could also be periodically driven at 2ω through nonlinear coupling between the electromagnetic vector potential A(ω) and the superconducting condensate [10][11][12] . The resulting free (driven) Higgs oscillation manifests itself in terahertz transmissivity as an oscillation at 2Δ (2ω).…”

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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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Lightwave-driven gapless superconductivity and forbidden quantum beats by terahertz symmetry breaking

Cited by 120 publications

References 31 publications

Theory of coherent-oscillations generation in terahertz pump-probe spectroscopy: From phonons to electronic collective modes

Theory of coherent-oscillations generation in terahertz pump-probe spectroscopy: From phonons to electronic collective modes

Light control of surface–bulk coupling by terahertz vibrational coherence in a topological insulator

Phase-resolved Higgs response in superconducting cuprates

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