Dynamics of optical injection of charge and spin currents in quantum wells

Abstract

We develop a dynamical theory for the optical injection of charge and spin current originating from the interferences between two coherent laser pulses of frequencies and 2. Multiband Bloch equations which include one-and two-photon interband transitions are derived. They also account for ac Stark shifts and intersubband two-photon transitions. The model is used to describe the case of time-dependent charge and spin current injection in a symmetric GaAs/AlGaAs quantum well. A comparison to the bulk case is also made. The separate contributions of the populations and intersubband coherences to the charge current and THz emission are identified. The influence of the Stark shifts and the inter-valence-band two-photon transitions are calculated and discussed.

Excitonic effects on the two-color coherent control of interband transitions in bulk semiconductors

“…10 Interband '1 + 2' interference in unbiased semiconductors, which is our interest here, allows independent control of electrical current injection 11,12 and spin current injection. 13,14,15,16,17,18 Furthermore, in noncentrosymmetric semiconductors, it allows independent control of carrier populations (i.e., absorption) 19,20 and carrier spin polarization. 21, 22 In each scenario, the experimenter can control the interference by adjusting the phases of the two colors.…”

Optical injection of charge current in quantum wires: Oscillations induced by excitonic effects

“…5,6 The matrix elements of the momentum operator x including spin-orbit coupling are defined by mn,k x = ͗m , k͉ x ͉n , k͘ and ⍀ mn,k denotes the interband frequency between the bands m and n at wave vector k. Under the spatial symmetry operations, the linear operator x transforms like the Cartesian component x, whereas the quadratic operator ͚ n x ͉n , k͗͘n , k͉ x / ͑⍀ nv,k − ͒ transforms like the product of two Cartesian components xx. Taking into account these symmetries, the excitonic selection rules can be derived.…”

“…5 However, it remains an open question how such processes may be affected by the Coulomb interaction. Interesting phenomena may be expected, as it will be shown in this paper.…”

Pure spin photocurrents

“…The energyĒ equals to E F /2 for a two-dimensional degenerate gas with the Fermi energy E F and k B T for a non-degenerate gas at the temperature T . The spin photocurrents (16) and (17) are contributed by spin-conserving optical transitions and, therefore, are proportional to the difference of subband splitting constants. The spectral behavior of the pure spin currents in both subbands repeats the derivative of the light absorption spectrum dη 21 (hω)/hω provided the intersubband absorption line is narrow enough.…”

“…Theoretically, the two-color generation and control of spin currents have been extensively analyzed [12,15,16,17]. Here we will consider, in order, the one-photon generation of pure spin currents in unbiased structures under interband, intersubband and intraband absorption of linearly polarized or unpolarized light and derive equations for the corresponding currents.…”