Giant third-order nonlinear susceptibilities for in-plane far-infrared excitation of single InAs quantum wells

Abstract

Third-order, free-carrier nonlinear susceptibilities, χ (3), have been measured between 19 and 23 cm −1 for three InAs/AlSb quantum wells with sheet densities between 2.5 × 10 12 cm −2 and 8 × 10 12 cm −2. We find that these wells are strongly nonlinear at far-infrared frequencies: odd harmonics ninth order have been observed at high incident intensities, and the peak value of χ (3) reaches ∼ 1 esu. This is several orders of magnitude larger than previously reported values for χ (3) in bulk n-GaAs (10 −4 esu)[1] and in polyacetylen (10 −7 esu)[2]. The large magnitude of χ (3) is attributed to the high carrier density in the InAs wells, and to the strong non-parabolicity of the conduction band in InAs. However, the free-carrier χ (3) for bulk InAs predicts a density-dependence different from that observed, and the measured decrease in χ (3) with increasing intensity indicates non-perturbative response. We find that the anisotropy of χ (3) displays the expected 4-fold symmetry.