Non-Markovian Exciton-Phonon Interactions in Core-Shell Colloidal Quantum Dots at Femtosecond Timescales

Abstract

We perform two-dimensional coherent spectroscopy on CdSe/CdZnS core/shell colloidal quantum dots at cryogenic temperatures. In the two-dimensional spectra, sidebands due to electronic coupling with CdSe lattice LO-phonon modes are observed to have evolutions deviating from the exponential dephasing expected from Markovian spectral diffusion, which is instantaneous and memory-less.Comparison to simulations provides evidence that LO-phonon coupling induces energy-gap fluctuations on the finite timescales of nuclear motion. The femtosecond resolution of our technique probes exciton dynamics directly on the timescales of phonon coupling in nanocrystals.

Room Temperature Inter-Dot Coherent Dynamics in Multilayers Quantum Dot Materials

“…24,27,30,33,34 The dephasing dynamics of this phonon mode and its coupling with electronic degrees of freedom has been the focus of several theoretical and experimental investigations, and it is still under scrutiny. [35][36][37][38][39] However, it affects the coherent dynamics on timescales much longer than the one investigated here. Thus, an in-depth analysis of this mode goes beyond the scope of this work.…”

Investigating the electronic structure of confined multiexcitons with nonlinear spectroscopies

“…29,30,32,33,104,107 The recent low-temperature 2D experiment reports impressive line narrowing which should, in principle, reveal fine structure states. 108,109 Another common approach consists in isolating the response from single nanocrystals. 23,84,85,[110][111][112][113] Performing a spatially resolved version of the current experiments should enable the observation of the electronic structure in the absence of ensemble broadening.…”

Perspective: multi-dimensional coherent spectroscopy of perovskite nanocrystals

“…Indeed, much of the physics of colloidal nanocrystals is inherited from their bulk parent compounds. Acoustic [30] and optical phonon modes [31] of a crystal lattice couple to excitons in nanocrystals, just as in bulk semiconductors. Especially for colloidal nanocrystals of extended dimensions such as nanoplatelets, many-body effects can also play a primary role in their optical properties [32].…”

“…The dynamics that evolve along the T time-delay also include incoherent processes such as spectral diffusion and population relaxation. Spectral diffusion dynamics, which refer to resonance energy fluctuations in time [11], are of particular interest on the ultrafast timescale as a microscopic origin of coherence dephasing [31] and spectral line-broadening. In an interesting report from Seiler et al [51] the spectral dynamics of CsPbI 3 nanocrystals were resolved as a function of T and compared with those of conventional CdSe nanocrystals and a molecular dye (shown in figure 5).…”