Signatures of many-particle correlations in two-dimensional Fourier-transform spectra of semiconductor nanostructures

Abstract

On the basis of a microscopic theory, the signatures of many-particle correlations in Two-Dimensional Fourier-Transform Spectra (2D-FTS) of semiconductor nanostructures are identified and compared to experimental data. Spectra in the photon energy range of the heavy-hole and light-hole excitonic resonances show characteristic features due to correlations, which depend on the relative polarization directions of the excitation pulses.Recent reports illustrate the potential of a novel method, known as "Two-Dimensional Fourier-Transform Spectroscopy" (2D-FTS), for the investigation of many-particle induced correlations in semiconductor structures [1,2,3]. 2D-FTS is based on a four-wave-mixing experiment, where three excitation pulses are separated in time and is heterodyne detected to fully characterize its phase. The signal is transformed into frequency domain ω t (emission frequency) and ω τ (excitation frequency), both with respect to real time t and time separation τ of the first two pulses, respectively. The third pulse is delayed with respect to the second one by T . 2D-FTS is widely used to study vibrational [4,5,6] and electronic excitations [7,8,9] in molecules. Applying 2D-FTS in the optical regime we investigate the complex interplay between exciton, biexciton and continuum excitations, in semiconductor nanostructures.In previous publications demonstrating 2D-FTS of semiconductors [1, 2, 3], the experimental results were compared to a phenomenological theory based on extending the Optical Bloch Equations to include terms that describe excitation induced dephasing (EID) [10,11] and excitation induced shift (EIS) [12]. Here, we use a microscopic theory to calculate 2D-FTS. Furthermore, the model predicts that the 2D-FTS qualitatively depend on the polarizations directions of the excitation pulses. Our results demonstrate that for 2D-FTS, the influence of many-particle correlations on the spectra can clearly be identified and are in agreement with the experimental findings.For the qualitative modeling of 2D-FTS in such systems and in order to keep the numerical requirement within reasonable limits we use a microscopic many-body theory and apply it to a one-dimensional tight-binding model. Therefore, a quantitative agreement between theory and experiment can not be expected. It has, however, been shown that many important signatures of nonlinear optical experiments performed on quantum wells can qualitatively well be reproduced by this model [13,14,15,16,17,18,19].The optical nonlinearities are treated up to third order in the coherent χ (3) -limit beyond the Hartree-Fock level. In order to separate the correlation effects from those due to the first-order Coulomb interaction (i.e., Hartree-Fock) we use a set of equations for the interband coherence P and two-exciton amplitudeB which in symbolic form reads [14,15,20,21] In fact, all terms in the microscopic version of the equations depend on the spatial indices of the tight-binding model as well as band indices, referring to electron, heavy-hole (h) and light-...

Signatures of four-particle correlations associated with exciton-carrier interactions in coherent spectroscopy on bulk GaAs

“…2(d) was observed previously in rephasing 2DFTS experiments on GaAs systems but the variation in the spectral structure for absorption energies within the continuum in Fig. 2(d) was not evident either because only the amplitude spectrum was detected 14,47 or the signal was measured over a narrower range of energies 15,22 . The dispersive lineshapes we observe for absorption at high energies within the continuum in this work were also not seen in recent experiments on InSe films 24 .…”

“…A strong enhancement of the exciton response in TFWM is observed, and the 2DFTS results indicate separate contributions to the exciton signal tied to degenerate and nondegenerate many-body interactions, consistent with previous reports 10,14,23,24 . The real part of the rephasing 2DFTS signal reveals a rich dispersive structure that was not evident in earlier 2DFTS studies of the exciton-continuum coupling because only the amplitude spectra were detected 14,47 or the signal was measured over a narrower range of energies 15,22 . This complex spectral structure prevents a simple assignment of EID and EIS effects to different parts of the spec-tra, as has been done in previous experiments under resonant excitation of the exciton 5 .…”

Polarization-dependent optical 2D Fourier transform spectroscopy of semiconductors

“…Calculations are performed by using a microscopic many-body theory (24). A 1D tight-binding model is used to make the numerical computations tractable.…”

“…The theoretical results are based on a many-body theory including correlations at a microscopic level with parameters chosen to match the experiments. Previous experimental results were compared with a phenomenological theory (11,23), or only the magnitude spectra were considered (24). Theoretical results without comparison to experiment have also recently been presented (25).…”

Coherent manipulation of quadrupole biexcitons in cuprous oxide by 2D femtosecond spectroscopy

“…3 Correlation spectroscopy of quadrupole biexcitons In analogy with nuclear magnetic resonance [20], 2D-spectroscopy has recently been implemented to study electronic and vibrational coupling in molecules [21][22][23] and in semiconductors [24][25][26]. In this section we utilize the unique sensitivity of this spectroscopy to couplings among various exciton resonances to predict the spectral signatures of biexcitons in cuprous oxide.…”