The dynamics of exciton tunneling and trapping in condensed xenon on ultrafast time scales

Reaction dynamics within a cluster environment

This perspective article reviews experimental and theoretical works where rare gas clusters and helium nanodroplets are used as a nanoreactor to investigate chemical dynamics in a solvent environment. A historical perspective is presented first followed by specific considerations on the mobility of reactants within these reaction media. The dynamical response of pure clusters and nanodroplets to photoexcitation is shortly reviewed before examining the role of the cluster (or nanodroplet) degrees of freedom in the photodynamics of the guest atoms and molecules.

Tunneling and reflection of an exciton incident upon a quantum heterostructure barrier

We investigate, in one spatial dimension, the quantum mechanical tunneling of an exciton incident upon a heterostructure barrier. We model the relative motion eigenstates of the exciton using a form of the one-dimensional hydrogen atom which avoids difficulties previously associated with 1D hydrogenic states. We obtain probabilities of reflection and transmission using the method of variable transmission and reflection amplitudes. Our calculations may be broadly divided into two sets. In the first set, we consider general qualitative aspects of exciton tunneling, such as the effect of different effective masses for electrons and holes and a relative difference in electron and hole barrier strengths. The second set models the tunneling of an exciton in a GaAs/Al(x)Ga(1-x)As heterostructure. In these calculations we find that, for energies such that the two lowest exciton states are coupled, the probability spectrum for transition from the ground state to the first excited state is identical to that for transition from the first excited state to the ground state. In addition, narrow peaks in the probability spectrum for transition are observed across this energy range for low dopant concentration x. Other interesting phenomena correlated with these peaks in the transition probability are reported.

Electron-vibron-breather interaction

We study the interaction of breathers in the context of a coupled electron-vibron lattice system. Starting with single-site excitations, it is demonstrated that constellations exist for which the coexistence of electronic and vibronic breathers is assured. The energy exchange between the vibrational and electronic subsystems and its impact on the breather formation are discussed in detail. The coupled electron-vibron dynamics shows a tendency toward energy redistribution into the vibronic degrees of freedom at the expense of the electronic energy content. Attention is paid to the relaxation dynamics in the energy exchange and we discuss the attainment of a steady regime for the coupled electron-vibron dynamics starting from a nonequilibrium state. It is demonstrated that the presence of breathers has a strong impact on the relaxation dynamics. Breathers can assist the relaxation process. With the help of a linear stability analysis, we show why the electronic subsystem acts as an energy donor while the vibron system serves as the energy acceptor. To this end we investigate the existence and stability of localized breathing eigenmodes capable of energy trapping. A frequency analysis reveals that strong exchange also occurs due to a temporal transition from single-frequency breathers to those oscillating with two frequencies and their temporal resonance interaction. Finally, the self-stabilized electron-vibron system relaxes to a combined electron-vibron breather. On increasing the electron-vibron coupling strength, only a vibronic phonobreather of large amplitude survives, whereas the electronic subsystem tends to energy equipartition.