Franck-Condon Factors as Spectral Probes of Polaron Structure

We apply the Merrifield variational method to the Holstein molecular crystal model in D dimensions to compute non-adiabatic polaron band energies and Franck-Condon factors at general crystal momenta. We analyze these observable properties to extract characteristic features related to polaron self-trapping and potential experimental signatures. These results are combined with others obtained by the Global-Local variational method in 1D to construct a polaron phase diagram encompassing all degrees of adiabaticity and all electron-phonon coupling strengths. The polaron phase diagram so constructed includes disjoint regimes occupied by "small" polarons, "large" polarons, and a newly-defined class of "compact" polarons, all mutually separated by an intermediate regime occupied by transitional structures

Rearrangement collisions between gold clusters

Collision processes between two gold clusters are investigated using classical molecular dynamics in combination with embedded atom (EA) potentials, after checking the reliability of EA results by contrasting them with first principles calculations. The Au projectiles considered are both single atoms (N=1) and clusters of N=2, 12, 13 and 14 atoms. The targets contain N= 12, 13 and 14 gold atoms. The initial projectile energy E is in the range 0 < E < 1.5 eV/atom. The results of the collision processes are described and analyzed in detail.Comment: LATeX file, 8 figures, uses svjour.cl

On the Generalized Kramers Problem with Oscillatory Memory Friction

The time-dependent transmission coefficient for the Kramers problem exhibits different behaviors in different parameter regimes. In the high friction regime it decays monotonically ("non-adiabatic"), and in the low friction regime it decays in an oscillatory fashion ("energy-diffusion-limited"). The generalized Kramers problem with an exponential memory friction exhibits an additional oscillatory behavior in the high friction regime ("caging"). In this paper we consider an oscillatory memory kernel, which can be associated with a model in which the reaction coordinate is linearly coupled to a nonreactive coordinate, which is in turn coupled to a heat bath. We recover the non-adiabatic and energy-diffusion-limited behaviors of the transmission coefficient in appropriate parameter regimes, and find that caging is not observed with an oscillatory memory kernel. Most interestingly, we identify a new regime in which the time-dependent transmission coefficient decays via a series of rather sharp steps followed by plateaus ("stair-like"). We explain this regime and its dependence on the various parameters of the system

Proximity-induced topological transition and strain-induced charge transfer in graphene/MoS2 bilayer heterostructures

Graphene/MoS2 heterostructures are formed by combining the nanosheets of graphene and monolayer MoS2. The electronic features of both constituent monolayers are rather well-preserved in the resultant heterostructure due to the weak van der Waals interaction between the layers. However, the proximity of MoS2 induces strong spin orbit coupling effect of strength ~1 meV in graphene, which is nearly three orders of magnitude larger than the intrinsic spin orbit coupling of pristine graphene. This opens a bandgap in graphene and further causes anticrossings of the spin-nondegenerate bands near the Dirac point. Lattice incommensurate graphene/MoS2 heterostructure exhibits interesting moire' patterns which have been observed in experiments. The electronic bandstructure of heterostructure is very sensitive to biaxial strain and interlayer twist. Although the Dirac cone of graphene remains intact and no charge-transfer between graphene and MoS2 layers occurs at ambient conditions, a strain-induced charge-transfer can be realized in graphene/MoS2 heterostructure. Application of a gate voltage reveals the occurrence of a topological phase transition in graphene/MoS2 heterostructure. In this chapter, we discuss the crystal structure, interlayer effects, electronic structure, spin states, and effects due to strain and substrate proximity on the electronic properties of graphene/MoS2 heterostructure. We further present an overview of the distinct topological quantum phases of graphene/MoS2 heterostructure and review the recent advancements in this field.Comment: 31 pages, 12 figure