[Fwd: Special seminar Wed 10]

[Condensed_Matter_Group]

Special Seminar in Condensed Matter Physics and Statistical Physics


Wednesday 10 February, 11:30 am
Luigi Stasi Seminar Room


Alexandre Reily Rocha
Instituto de Fisica Teorica, Unesp, Sao Paulo, Brazil

Optical properties of two-dimensional materials: From absorption to Raman
spectroscopy with DFT


Abstract:
During the last decade, novel two-dimensional (2D) semiconducting
materials have been synthesized and characterised. As a result, there
have been several theoretical and experimental proposals to incorporate
2D materials for designing next generation electronic and optoelectronic
devices. In particular, it has been demonstrated that light absorption
in phosphorus-based monolayers can span the whole visible spectrum,
suggesting they could be used for optolectronic applications. A key
ingredient for optical applications is the presence of excitons and
their subsequent diffusion along a donor material. This is influenced by
the character of the different excitations taking place, as well as, the
exciton binding energy. At the same time the anisotropic character of
black phosphorus can give rise to interesting optical responses
depending on the polarization, and even more so at the edges of the
sample. This could interesting phenomena such as unusual thermal
conductivity at the edges of the material compared to the bulk.

Therefore, In this work we use accurate density functional theory
calculations to probe the optical response of different phosphorus
allotropes. First, by means of GW-BSE methodology to we elucidate the
most important optical transitions, exciton energy spectrum as well as
exciton extension in di fferent types of phosphorene materials. In
addition, we solve the Schrodinger equation for different 2D screened
potentials in a hydrogenic model and estimate the 2D exciton energy
levels and radius extension. Finally, we also study the Raman spectrum
on the edges of black phosphorene to show the presence of forbidden
Raman modes seen in experiments, which arise from edge reconstruction.