Signatures of nonadiabatic BCS state dynamics in pump-probe conductivity

Krull, H.; Manske, Dirk; Uhrig, Götz S.; Schnyder, Andreas P.

doi:10.1103/physrevb.90.014515

Cited by 62 publications

(90 citation statements)

References 38 publications

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“…Theoretical investigations along these directions have appeared in the literature in recent years [19][20][21][22] addressing questions like the thermalization of pump-excited Mott or Kondo insulators [23,24] and the role of lattice vibrations [25], orbital degrees of freedom [26] and competing orders [27,28] in the relaxation dynamics. The dynamics of conventional superconductors has also been studied with reference to pump-probe experiments [29][30][31] or in the presence of electron-phonon interactions [32][33][34] and Coulomb repulsion [35]. In the context of ultracold atomic systems, the research has focused on the s-wave weak coupling BCS regime [36][37][38][39], with recent attempts to extend the analysis to the crossover into the BEC regime [40,41] and to exotic order-parameter symmetries [42,43].…”

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confidence: 99%

Transient Dynamics ofd-Wave Superconductors after a Sudden Excitation

2015

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Motivated by recent ultrafast pump-probe experiments on high-temperature superconductors, we discuss the transient dynamics of a d-wave BCS model after a quantum quench of the interaction parameter. We find that the existence of gap nodes, with the associated nodal quasiparticles, introduces a decay channel which makes the dynamics much faster than in the conventional s-wave model. For every value of the quench parameter, the superconducting gap rapidly converges to a stationary value smaller than the one at equilibrium. Using a sudden approximation for the gap dynamics, we find an analytical expression for the reduction of spectral weight close to the nodes, which is in qualitative agreement with recent experiments.PACS numbers: 74.20.Rp,74.40.Gh,05.70.Ln Introduction. -Recent advances in time-resolved spectroscopies have triggered a growing interest in the transient dynamical behavior of high-temperature superconductors optically excited far from equilibrium. By shining the sample with intense ultrafast pulses (pump) one can trigger nonequilibrium transient states, whose physical properties are then recorded by a second pulse (probe) which hits the sample with a given time delay. This approach opens up a wealth of information unavailable to conventional time-averaged spectroscopies [1][2][3][4][5][6][7][8][9]. When used in combination with angle-resolved photoemission spectroscopy (ARPES), these ultrafast methods allow us to track and follow in real time the evolution of quasiparticle modes in different momentum sectors, such as those close to the gap nodes and antinodes of d-wave cuprate superconductors [10][11][12]. In addition, when irradiation is sufficiently strong and optically tailored in such a way to selectively excite specific modes, one can even stabilize transient states with fundamentally different physical properties [13][14][15]. A spectacular example is given by recent experiments reporting signatures of light-induced metastable superconductivity in cuprates at much higher temperature than at equilibrium [16,17].

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confidence: 99%

Transient Dynamics ofd-Wave Superconductors after a Sudden Excitation

2015

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“…Before this experiment [15], the amplitude Higgs mode had been observed only in a special case, 2H -NbSe 2 , where SC coexists with a charge density wave [4][5][6]18,19]. Theoretical studies of the SC order parameter dynamics have so far primarily focused on the static mean-field dynamics [1][2][3][5][6][7][8][9][10][11][12][13]17,19,[22][23][24]. One important conclusion of these works is that the frequency of the Higgs amplitude mode (ω H ) should coincide with the SC gap (2 SC ) in the BCS regime [27], which is a threshold for quasiparticle excitations.…”

Section: Introductionmentioning

confidence: 99%

Multiple amplitude modes in strongly coupled phonon-mediated superconductors

et al. 2016

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We study collective amplitude modes of the superconducting order parameter in strongly coupled electronphonon systems described by the Holstein model using the nonequilibrium dynamical mean-field theory with the self-consistent Migdal approximation as an impurity solver. The frequency of the Higgs amplitude mode is found to coincide with the superconducting gap even in the strongly coupled (beyond BCS) regime. Besides the Higgs mode, we find another collective mode involving the dynamics of both the phonons and the superconducting order parameter. The frequency of this mode, higher than twice the renormalized phonon frequency in the superconducting phase, is shown to reflect a strong electron-mediated phonon-phonon interaction. Both of collective modes are predicted to contribute to time-resolved photoemission spectra after a strong laser pump as vertex corrections to produce resonance peaks, which allows one to distinguish them from quasiparticle excitations.

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“…Later studies [17,18] mapped out the full quantum quench "phase diagram" for weakly coupled s-wave BCS superconductors finding that three distinct regimes occur depending on the strength of the quench: Volkov-and-Kogan-like behavior, persistent oscillations, and exponential vanishing of the order parameter. Most recent research [27][28][29][30] fueled by experimental breakthroughs [25,31,32] investigates nonadiabatic dynamics of s-wave BCS superconductors in response to fast electromagnetic perturbations. Closely related subjects developing in parallel are exciton dynamics [33], collective neutrino oscillations [34,35], quenched p-wave superfluids [36,37], etc.…”

Section: Introductionmentioning

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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Signatures of nonadiabatic BCS state dynamics in pump-probe conductivity

Cited by 62 publications

References 38 publications

Transient Dynamics ofd-Wave Superconductors after a Sudden Excitation

Transient Dynamics ofd-Wave Superconductors after a Sudden Excitation

Multiple amplitude modes in strongly coupled phonon-mediated superconductors

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

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