Density matrix theory of coherent ultrafast dynamics

Kuhn, Tilmann

doi:10.1007/978-1-4615-5807-1_6

Cited by 72 publications

(92 citation statements)

References 59 publications

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“…Again the complications vanish under the assumption, that scattering is neglected in the leads. In the same way one obtains (143) where Eqs (139,140,141) have been subsequently applied (partially in the form for advanced functions).…”

Section: Spatial Boundary Conditions and Contactsmentioning

confidence: 99%

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Semiconductor superlattices: a model system for nonlinear transport

2002

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Electric transport in semiconductor superlattices is dominated by pronounced negative differential conductivity. In this report the standard transport theories for superlattices, i.e. miniband conduction, Wannier-Stark-hopping, and sequential tunneling, are reviewed in detail. Their relation to each other is clarified by a comparison with a quantum transport model based on nonequilibrium Green functions. It is demonstrated how the occurrence of negative differential conductivity causes inhomogeneous electric field distributions, yielding either a characteristic sawtooth shape of the current-voltage characteristic or self-sustained current oscillations. An additional ac-voltage in the THz range is included in the theory as well. The results display absolute negative conductance, photon-assisted tunneling, the possibility of gain, and a negative tunneling capacitance. 2 Notation and list of symbolsThroughout this work we consider a superlattice, which is grown in the z direction. Vectors within the (x, y) plane parallel to the interfaces are denoted by bold face letters k, r, while vectors in 3 dimensional space are r, k, . . . . All sums and integrals extend from −∞ to ∞ if not stated otherwise.The following relations are frequently used in this work and are given here for easy reference:

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Section: Spatial Boundary Conditions and Contactsmentioning

confidence: 99%

“…A recent overview can be found in [140]. Density matrix theory has been applied to superlattice transport in [73] for the evaluation of currents between nonequivalent levels.…”

Section: Appendix a Sequential Tunneling With Density Matricesmentioning

confidence: 99%

Semiconductor superlattices: a model system for nonlinear transport

2002

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“…In the model we present, these equations have a similar form to those given in Ref. 8 except that it includes exchange scattering processes in the collisional part and it neglects all intrasubband polarizations as well as contributions to interband polarization from other than the first transition.…”

Section: General Formalismmentioning

confidence: 99%

“…The first is the nonequilibrium Green's function theory using for example the time-loop S-matrix method [1][2][3][4] and the second is the density matrix theory. [5][6][7][8] This paper extends ultrafast carrier dynamics models which address the sub-1-ps time scale where carrier-carrier ͑c-c͒ scattering is the dominant mechanism. We analyze a separate confinement heterostructure ͑SCH͒ quantum well with multiple parabolic subbands in each band using the density matrix formalism while considering all possible nonvanishing Coulomb scattering events within the multiplesubband system.…”

Section: Introductionmentioning

confidence: 95%

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Relaxation of a kinetic hole due to carrier-carrier scattering in multisubband single-quantum-well semiconductors

2003

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We describe a theoretical model for carrier-carrier scattering in an inverted semiconductor quantum well structure using a multisubband diagram. The model includes all possible nonvanishing interaction terms within the static screening approximation, and it enables one to calculate accurately the temporal evolution of the carrier densities and the gain following a perturbation by a short optical pulse. We present a theoretical formalism and detailed numerical calculations. The addition of more than one subband in each band as well as the use of all exchange terms yields several results. First, the degree of gain saturation is reduced while, at the same time, the recovery is faster as scattering events among different subbands take place. Also, carrier transfer between subbands is observed which modifies the overall carrier dynamics.

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