Fig. 4: Linearised dispersion relation.
From: Directional Goldstone waves in polariton condensates close to equilibrium
Experimental data of the excitation spectrum from Fig. 3d, zoomed in close to the condensate energy and momentum. The diagonal dashed-black line is the sound dispersion obtained from the same fitting parameters as used in Fig. 3d. Parabolic dispersion relations associated with the condensate energy and the high-momentum part of the spectrum are reported for clarity using dashed blue and grey lines, respectively. The vertical dashed line is the cutoff wavevector \(\frac{1}{\xi }\) above which the dispersion is almost parabolic.
