arXiv subjects

Bernd Hönerlage

Publications and source records attributed to Bernd Hönerlage.

3 recordsLinked to original sources

arXiv2019

On the Exciton Fine-Structure of Transition-Metal Dichalcogenides Mono-Layers

In order to discuss the exciton fine-structure of transition-metal dichalcogenides mono-layers, excitons are first defined in the subspace of electron- and hole states, including the lowest conduction band (LCB) and the uppermost valence band (UVB). Both bands are spin degenerate at the Gamma-point. All other states are neglected. The resulting exciton states are analyzed in the framework of an invariant expansion of a model Hamiltonian: The spin-orbit coupling in the conduction- and valence band is simulated by introducing a fictive magnetic field, giving rise to a splitting of the electron- and hole states outside the $Γ$-point. Then the electron-hole exchange-interaction is introduced into the exciton Hamiltonian. It is due to the fact that electron and hole are indistinguishable particles in the exciton problem. In D3h crystal symmetry this electron-hole exchange-interaction has two different contributions: While a first term accounts for an energy re-normalization of all exciton states, a second term does not influence the optical active (spin-singlet) states but affects only the optical inactive (spin-triplet) states, which become mixed in-between the different exciton series.

cond-mat.mes-hall↗

arXiv2016

Nonlinear strong coupling between sub-band excitons: a new coherent path for ultrafast relaxation

We demonstrate theoretically and experimentally that the nonlinear interaction between excitations whose harmonic energies coincide gives rise to a strong coupling that opens a new coherent ultrafast energy relaxation path. Instead of an incoherent decay of excitations, that should take a finite time that depends on the energy difference between the initial state and the final state, the nonlinear interaction allows their coherent superposition and thus an instantaneous transfer of the excitation over energies as large as the electron-volt. Such a situation should be encountered in many systems. We demonstrate that such a model applies also for excitons in single-wall carbon nanotubes (SWCNT) where a strong nonlinear Coulomb interaction occurs between $\rm E_{11}$ and $\rm E_{22}$ states. This explains a wide panel of observations about optoelectronic properties of the SWCNT and gives a coherent picture of their features like the exciton-line spectral positions, exciton collisions and their ultrafast relaxation, as well as the low light-emission efficiency of the nanotubes.

cond-mat.mes-hall↗

arXiv2013

Biexciton, single carrier, and trion generation dynamics in single-walled carbon nanotubes

We present a study of free carrier photo-generation and multi-carrier bound states, such as biexcitons and trions (ionized excitons), in semiconducting single-walled carbon nanotubes. Pump-and-probe measurements performed with fs pulses reveal the effects of strong Coulomb interactions between carriers on their dynamics. Biexciton formation by optical transition from exciton population results in an induced absorption line (binding energy 130 meV). Exciton-exciton annihilation process is shown to evolve at high densities towards an Auger process that can expel carriers from nanotubes. The remaining carriers give rise to an induced absorption due to trion formation (binding energy 190 meV). These features show the dynamics of exciton and free carriers populations.

cond-mat.mes-hall↗