Multiresonant Multidimensional Spectroscopy of Surface-Trapped Excitons in PbSe Quantum Dots.

Recent work spectrally isolated and measured the quantum states associated with ultrafast relaxation from an initially excited 1S excitonic state to a lower energy state that is present in an inadequately capped PbSe quantum dot sample. The relaxed state was attributed to a surface-trapped exciton (STE). This letter reports the line-narrowed, multiresonant, two-dimensional spectrum of this sample. The multidimensional spectrum is unusual because diagonal peaks are absent, but there is a strong cross-peak between the 1S and STE transitions. Theoretical modeling provided values for the coherent and incoherent dynamics, the relative exciton and biexciton transition moments, the Coulombic coupling, and the homogeneous and inhomogeneous broadening. This work demonstrates the feasibility of using multiresonant methods to probe the quantum state dynamics of interface states in nanostructures.