Intraband Dynamics at the Semiconductor Band Edge: Shortcomings of the Bloch Equation Method

Axt, Vollrath M.; Bartels, G.; Stahl, A.

doi:10.1103/physrevlett.76.2543

Cited by 69 publications

(60 citation statements)

References 12 publications

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“…The dynamical behavior of electrons and holes in BSSLs have been investigated both theoretically [1][2][3][4][5][6][7] and experimentally [7][8][9][10] by a large number of authors. The basic intraband dynamics can be understood in terms of the stationary states of non-interacting electrons in the superlattice potential in the presence of a uniform, along-axis static electric field, F .…”

Section: Resultsmentioning

confidence: 99%

“…There has been considerable interest in recent years in the development of a clear theoretical understanding and treatment of the nonlinear optical response of semiconductor nanostructures to ultrashort optical pulses [1][2][3][4][5][6][7]. One common approach to this problem has been to expand the response in powers of the optical field [2,4,[5][6][7].…”

Section: Introductionmentioning

confidence: 99%

“…One common approach to this problem has been to expand the response in powers of the optical field [2,4,[5][6][7]. This approach has been very successful for the treatment of many different nonlinear effects.…”

Section: Introductionmentioning

confidence: 99%

“…This approach has been very successful in describing a number of phenomena such as the dynamic Stark effect. However, it has been shown [5,8] that it is not suited to structures in which excitonic effects are strong, such as biased semiconductor superlattices (BSSLs), as it underestimates the electron-hole correlations in the intraband response. In this work, we employ the excitonic Bloch equations of Hawton and Dignam [3] to calculate the intraband and interband response of a BSSL to ultrashort optical pulses.…”

Section: Introductionmentioning

confidence: 99%

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The Interplay of Intraband and Interband Polarization in the Ultrafast Response of Biased Semiconductor Superlattices

Dignam¹,

Hawton²,

Yang³

et al. 2005

Acta Phys. Pol. A

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We present the results of a new excitonic formalism for the treatment of ultrafast dynamics in asymmetric semiconductor multiple quantum well structures. The method is infinite order in the optical field, with truncation of the infinite hierarchy of dynamical equations being accomplished via a factorization of six-particle correlation functions into a product of twoand four-particle ones. We use this formalism to calculate the THz emission and degenerate four-wave mixing signals from biased semiconductor superlattices under different excitation conditions. We present a number of density-dependent effects that demonstrate the central role that the intraband polarization plays in determining and modifying the nonlinear ultrafast response of the system.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Interplay of Intraband and Interband Polarization in the Ultrafast Response of Biased Semiconductor Superlattices

Dignam¹,

Hawton²,

Yang³

et al. 2005

Acta Phys. Pol. A

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“…Secondly, the doubly resonant condition can always be accomplished by adjusting the static electric field and tuning the input light. And thirdly, the problem of signal absorption can also be avoided in undoped superlattices.Though it has been well-known that the exciton correlation plays an essential role in THz emission from Bloch oscillation in optically excited superlattices [12], its effect on difference-frequency in biased superlattices is still unclear. This question will be addressed in this Letter, and it will be shown that the excitonic effect can enhance the emission power by at least two orders of magnitude, which, however, is absent in, e.g., difference-frequency in doped quantum wells [7].…”

mentioning

confidence: 99%

Tunable terahertz emission from difference frequency in biased superlattices

Liu

Zhu

2004

Applied Physics Letters

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The terahertz emission from difference-frequency in biased superlattices is calculated with the excitonic effect included. Owing to the doubly resonant condition and the excitonic enhancement, the typical susceptibility is larger than 10 −5 m/V. The doubly resonant condition can always be realized by adjusting the bias voltage and the laser frequencies, thus the in-situ tunable emission is efficient in the range of 0.5-6 terahertz. Continuous wave operation with 1% quantum efficiency and µW output power is feasible while the signal absorption in undoped superlattices is negligible. [7]. With state-of-the-art design of superlattices, a prototype of quantum-cascade THz lasers has been demonstrated recently [8]. Among these mechanisms for THz emission, the difference-frequency process is of special interest because of its in-situ tunability, intense output under phasematching condition, and flexibility of operating at both continuous wave and pulse modes [9]. Furthermore, doubly resonant condition, in which both the input and output are near resonant with transitions in the system, can also be exploited to enhance the difference-frequency [7]. Doubly resonant difference-frequency in biased superlattices was also proposed for THz emission [10,11]. Under doubly resonant condition, the Bloch oscillation is sustained and amplified by the effective THz potential resulting from the dipole interaction of excitons and the bichromatic input light, generating efficient THz radiation [10]. Several advantages of this method over other difference-frequency schemes can be expected: First, the applied electric field breaks the inversion symmetry of the system, leading to a large intraband dipole matrix element. Secondly, the doubly resonant condition can always be accomplished by adjusting the static electric field and tuning the input light. And thirdly, the problem of signal absorption can also be avoided in undoped superlattices.Though it has been well-known that the exciton correlation plays an essential role in THz emission from Bloch oscillation in optically excited superlattices [12], its effect on difference-frequency in biased superlattices is still unclear. This question will be addressed in this Letter, and it will be shown that the excitonic effect can enhance the emission power by at least two orders of magnitude, which, however, is absent in, e.g., difference-frequency in doped quantum wells [7].The second-order difference-frequency susceptibility is the key quantity determining the emission intensity. In principle, it can be evaluated from the textbook formula derived with the double-line Feynman diagrams [13]. Under the doubly resonant condition, the differencefrequency susceptibility [13]where Ω i is the frequency of the input light polarized at e ji direction, ε αα ′ (α, α ′ = a, b, or 0) is the transition energy between the exciton states |a , |b , and the semiconductor ground state |0 , d αα ′ is the dipole matrix element, γ 2 and γ 1 are the interband and intraband dephasing rates, respectively, V is the vol...

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