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Exciton ionization in transition-metal dichalcogenides

Speaker: 
Thomas G. Pedersen (Aalborg University, Denmark)
Date: 
Wed, 10/02/2016 - 11:00am to 12:00pm
Location: 
Physics Conference Room (S11-02-07)
Host: 
Vitor M. Pereira
Event Type: 
Seminars

Abstract

In photodetectors and solar cells, optically generated excitons must be ionized to separate electrons and holes. If the excitons are strongly bound, thermal ionization is inefficient. A strong electric field, however, can greatly enhance the ionization rate. We study this process theoretically for mono- and multilayer transition-metal dichalcogenides within a modified Wannier exciton model. The effects of dimensionality and screening on the exciton binding energy are discussed. In the presence of a strong electric field, the exciton energies become complex resonances. We extract the ionization (tunnelling) rate using two complementary approaches: complex scaling and hypergeometric resummation [1]. By applying these techniques to Mo and W based compounds we compute the field- dependence of the ionization rate for both monolayer and multilayer photodetectors, thereby obtaining a fundamental limit for the photoresponse rate [2].

1. H. Mera, T.G. Pedersen, and B.K. Nikolic, “Nonperturbative quantum physics from low-order perturbation theory”, Phys. Rev. Lett. 115, 143001 (2015).
2. T.G. Pedersen et al. “Exciton ionization in multilayer transition-metal
dichalcogenides”, submitted.

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