Two-quantum many-body coherences in two-dimensional fourier-transform spectra of exciton resonances in semiconductor quantum wells.
Karaiskaj D, Bristow AD, Yang L, Dai X, Mirin RP, Mukamel S, Cundiff ST. Two-quantum many-body coherences in two-dimensional fourier-transform spectra of exciton resonances in semiconductor quantum wells. Phys Rev Lett. 2010 Mar 19; 104(11):117401.