Femtosecond Formation of Coupled Phonon-Plasmon Modes in InP: Ultrabroadband THz Experiment and Quantum Kinetic Theory

Huber, Rupert; Kübler, C.; Tübel, S.; Leitenstorfer, Alfred; Vu, Q. T.; Haug, H.; Köhler, Fabian; Amann, M.-C.

doi:10.1103/physrevlett.94.027401

Cited by 95 publications

(59 citation statements)

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“…For correlations beyond the mean field we should observe deviations. This is the case in the recently observed response of InP [3], where a coupling between The time evolution of the inverse dielectric function in GaAs. The labels from top to bottom denote the time t. The pumb pulse was at t0 = −40fs and the probe pulse has a full-width at half-maximum of 27f s. Circles are data from [1,2], solid lines show the electronic part with intrinsic polarization (19) and dotted lines the electronic part alone (17).…”

Section: (T T − T ) (15)mentioning

confidence: 92%

“…At times 100 fs-200 fs the formation of collective modes is described again sufficiently well. For InP we use parameters according to [3] namely ω LO /2π = 10.3 THz, ω TO /2π = 9 THz, γ = 0.2 ps −1 , and ǫ ∞ = 9.6. The aim of the present paper was to separate the gross feature of the formation of collective modes at transient times which are due to simple mean-field fluctuations.…”

Section: (T T − T ) (15)mentioning

confidence: 99%

“…Such ultrafast excitations in semiconductors have been satisfactorily described by calculating nonequilibrium Green's functions [7,8]. This approach allows one to describe the formation of collective modes [3,9] and even exciton population inversions [10].…”

mentioning

confidence: 99%

“…The femtosecond spectroscopy has opened the exciting possibility to observe directly the formation of collective modes and quasiparticles in interacting many-body systems. This formation is reflected in the time dependence of the dielectric function [1,2,3] or terahertz emission [4]. For an overview over theoretical and experimental work see [5,6].…”

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confidence: 99%

“…In the further analysis we will follow closely the experimental way of analyzing the two-time response function [3]. The pump pulse is creating charge carriers in the conduction band at time t 0 and the probe pulse is sent a time t D later.…”

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confidence: 99%

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Femtosecond formation of collective modes due to mean-field fluctuations

2005

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Starting from a quantum kinetic equation including the mean field and a conserving relaxationtime approximation we derive an analytic formula which describes the time dependence of the dielectric function in a plasma created by a short intense laser pulse. This formula reproduces universal features of the formation of collective modes seen in recent experimental data of femtosecond spectroscopy. The presented formula offers a tremendous simplification for the description of the formation of quasiparticle features in interacting systems. Numerical demanding treatments can now be focused on effects beyond these gross features found here to be describable analytically.PACS numbers: 71.45. Gm, 78.47.+p, 42.65.Re, 82.53.Mj The last ten years have been characterized by an enormous activity about ultrafast excitations in semiconductors, clusters, or plasmas by ultrashort laser pulses. The femtosecond spectroscopy has opened the exciting possibility to observe directly the formation of collective modes and quasiparticles in interacting many-body systems. This formation is reflected in the time dependence of the dielectric function [1, 2, 3] or terahertz emission [4]. For an overview over theoretical and experimental work see [5,6]. Such ultrafast excitations in semiconductors have been satisfactorily described by calculating nonequilibrium Green's functions [7,8]. This approach allows one to describe the formation of collective modes [3,9] and even exciton population inversions [10].The experimental data in semiconductors like GaAs [2] or InP [3] reveal similar features. These features are explained by several numerically demanding calculations. Since some common features are robust, i.e., independent of the actual used material parameters, it should be possible to describe them by a simple theory. The origin of such robust features likely rests in the short-or transienttime behavior itself. At short times higher-order correlations have no time yet to develop, therefore the dynamics is controlled exclusively by mean-field forces.Based on the mean-field character of the short-time evolution we intend to derive a time-dependent response function from the mean-field linear response. We will start from a conserving relaxation-time approximation which dates back to an idea of Mermin [11,12]. Our aim is a simple analytic formula suitable for fits of experimental data.The electron motion is controlled by the kinetic energŷ E, the external perturbationV ext and the induced meanfield potentialV ind . The corresponding kinetic equation for the one-particle reduced density matrixρ readṡwith the relaxation time τ and a local equilibrium density matrixρ l.e. determined in the following. We will calculate the response in the momentum representationwhere |p is an eigenstate of momentum p. For interpretations it is more convenient to transform the reduced density matrix to the Wigner distribution in phase spacewhere R is the spatial coordinate. The relaxation process in Eq.(1) tends to establish a local equilibrium. Following Mermin...

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Section: (T T − T ) (15)mentioning

confidence: 92%

Section: (T T − T ) (15)mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Femtosecond formation of collective modes due to mean-field fluctuations

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Terahertz Photoconductivity

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Excitation and Time‐Evolution of Coherent Optical Phonons

Hase

Misochko

Ishioka

2010

Dynamics at Solid State Surfaces and Interfaces

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Coherent optical phonons are the lattice vibrations of the optical branches excited in-phase over a macroscopic spatial region by ultrashort laser pulses. Their generation and relaxation dynamics have been investigated by optical pump-probe techniques in a broad range of solid materials. When probed with a linear optical process such as reflection, the probing depth is from nanometers to micrometers determined by the absorption coefficient and the laser wavelength. By employing a nonlinear optical process such as second harmonic generation, however, it is possible to monitor coherent phonons at surfaces and interfaces exclusively. When the photoexcitation creates electron-hole plasma, coherent phonons can also serve as an ultrafast probe of nonequilibrium electron-phonon coupling. Using an optical pulse train with a designed repetition rate, coherent phonons can be excited to large amplitudes, which is expected to be a promising strategy toward nonthermal phase transitions in solids. New femtosecond beam sources such as X-ray and THz pulses offer complementary techniques to probe the ultrafast phononic and electronic dynamics under extremely nonequilibrium conditions. Coherent Phonons in Group V SemimetalsBismuth (Bi) and antimony (Sb) have been model systems for optical studies on coherent phonons because of their relatively low frequencies and large amplitudes in the optical reflectivity. They both have an A7 crystalline structure and sustain two Raman-active optical phonon modes shown in Figure 10.1e. The coherent phonons of A 1g and E g symmetries have been detected as periodic modulations of the reflectivity (Figure 10.1a) in the order of DR=R¼ 10 À6 to 10 À2 depending on the excitation density. Recently, the coherent A 1g phonons of Bi have gained a renewed interest as the benchmark for femtosecond X-ray diffraction experiments.

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Femtosecond Formation of Coupled Phonon-Plasmon Modes in InP: Ultrabroadband THz Experiment and Quantum Kinetic Theory

Cited by 95 publications

References 16 publications

Femtosecond formation of collective modes due to mean-field fluctuations

Femtosecond formation of collective modes due to mean-field fluctuations

Terahertz Photoconductivity

Excitation and Time‐Evolution of Coherent Optical Phonons

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