Fig. 3: Comparison of nonlinearity of the IE polariton with A exciton polariton.

a Energy of the lower and upper branch of the IE polariton as a function of the polariton density at zero-detuning k_∥. The movement of the lower branch is more than the upper branch due to the combined effect of exciton-exciton interaction and saturation. The error bars in energy represent the uncertainty in determining the peak of the Lorentzian fit (polariton energy) to the reflection data. b g\({}_{{{{{{{{\rm{LP}}}}}}}}}^{{{{{{{{\rm{IE}}}}}}}}}\) (g\({}_{{{{{{{{\rm{LP}}}}}}}}}^{{{{{{{{\rm{A}}}}}}}}}\)) as a function of the IE (A) lower branch polariton density at zero-detuning k_∥. g_LP is defined as the local slope of the polariton energy vs. polariton density graph. g\({}_{{{{{{{{\rm{LP}}}}}}}}}^{{{{{{{{\rm{A}}}}}}}}}\) and g\({}_{{{{{{{{\rm{LP}}}}}}}}}^{{{{{{{{\rm{IE}}}}}}}}}\) are calculated from the lower branch of A polariton and IE polariton, respectively. Note that the g_LP of IE polariton ~(100 ± 2) μeV μm² is almost 10 times larger than the g_LP of A exciton polariton ~(10 ± 0.2) μeV μm². All the power-dependent nonlinear measurements were carried out using a pulsed supercontinuum laser (20 ps pulsewidth) with proper bandpass filter in the input to excite only one polariton species. The polariton density corresponds to the specific branch being excited. The density error bars take into account the error in measuring power and determining the energy of the polariton and linewidth from the Lorentzian fits. The error bars in g_LP consider the error in determining the density and the energy of the polariton.