Optical coherent transient effects in magnetoactive GaAs/AlGaAs quantum well structure

Abstract

The effect of an external magnetic field on optical coherent transient phenomena has been analyzed for semiconductor quantum well structures (QWS). The Lüttinger Hamiltonian is used to incorporate the complex valence band structure which is modified due to the application of the magnetic field. We have considered a GaAs/AlGaAs QWS with magnetic field applied in the direction perpendicular to the plane of the well. We get two quantum levels due to confinement, and doubly degenerate heavy-hole and light-hole bands corresponding to each quantum level, thus leading to eight hole subbands. This results in an 8×8 Hamiltonian in an appropriately chosen basis. Energy eigenvalues and eigenvectors have been calculated by numerically diagonalizing the above Hamiltonian. The absorption characteristics and the optical coherent transient phenomena have been studied by solving the effective semiconductor Bloch equations in the weak excitation regime. The polarization induced in conjunction with the results obtained by solving the modified Lüttinger Hamiltonian has been used to analyze the transient characteristics. We observe a blueshift in transition energy with an increase in magnetic field. The features are changed dramatically when one includes band mixing. The crossing of subbands in the absence of band-mixing effects changes over to anticrossing behavior when band mixing is included. Multiple oscillations are observed in the optical nutation signal that can be attributed to band-mixing effects. Absorption spectra also show a significant blueshift with an increase in magnetic field and additional peaks appear when band mixing is included.

Optical nutation induced by transition between levels inside and outside the well in a core–shell CdSe/ZnS quantum dot

“…It is shown in figure 3 that the nutation signal decays rapidly: it arises due to the transient polarization induced in the QD and decays for the reason that the absorption coefficient is directly proportional to the population difference of the electrons, which is decreasing rapidly. Similar decay behaviour for quantum wires and micro-cavity was reported in [13,14,[23][24][25].…”

“…Optical nutation has been studied in bulk semiconductors using a two-level model by Singh [12]. Sen has studied it in semiconductor QWs and QWRs; even those low-dimensional structures were put into a strong magnetic field [13,14]. However, there has been little work about optical nutation in core-shell QDs.…”

Wavefunction analysis and optical nutation in magnetized semiconductor quantum wires exhibiting multiple valence subbands

“…Photoinduced transitions occur between these 8 hole subbands and the lowest conduction band. Consequently, one finds the Luttinger Hamiltonian as 8 × 8 matrix for a system of GaAs/AlGaAs QWR structure immersed in the moderately strong static magnetic field [18].…”

“…The coherent transient phenomena in presence of magnetic field have been analyzed in GaAs/AlGaAs QWs, with particular emphasis on the effect of bandmixing [18]. In this paper, we use the formalism of Ref.…”

“…In this paper, we use the formalism of Ref. [18] and modify it for application to quantum wires. The calculation of hole wavefunctions in a GaAs/AlGaAs quantum wire structure with multiple valence subbands under the influence of magnetic field is presented.…”