Hi Everyone,
This Monday at 2:00pm in the Division Room we will have a special group
meeting. Professor Mark T. Lusk from the Colorado School of Mines will be
presenting. You can find a title and abstract for his talk below.
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*Partially Coherent Exciton Transport in Silicon Quantum Dot Mesomaterials*
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Recent progress in understanding electronic wave functions in condensed
matter nanostructures has led to an ability to synthesize isolated, quantum
confined building blocks with a variety of tailored optical properties. No
matter what optical gap is engineered and how cleverly exciton energy is
redistributed, though, novel materials composed of such nanostructures need
to also exhibit efficient carrier dynamics. Transport of energy and charge
is now the central issue in harnessing the true power of quantum dot
materials for solar and many other uses. This is a critical bottleneck in
the science because charge and exciton transport tend to proceed via low
mobility, incoherent hopping associated with weak electronic coupling and
high reorganization energies in these nanostructures.
A number of promising strategies seek to improve energy and charge
transport between quantum dots by focusing on important properties such as
translational symmetry, electronic overlap, matrix encapsulation, and
crystalline orientation. Our approach, though, is to consider the entire
assembly as a *quantum dot mesomaterial* (QDM), wherein entirely new
transport physics may emerge from the complex interactions between
components. For instance, the superb exciton harvesting efficiency of
photosynthetic complexes is at least partly due to conditions that support
an element of coherent character for exciton transport. Here proteins and
pigments are exquisitely structured and combined so that they perform a
number of integrated functions—e.g. proteins serve to correlate electronic
excitations on neighboring pigments, supporting coherence and allowing
exciton transport with a degree of wave-like character.
We seek to design materials composed of quantum dots in which components
may carry out integrated tasks that optimize dynamics ranging from
incoherent random walks to coherent transport. An emphasis is placed on the
robustness of such transport in the face of geometric uncertainties
intrinsic to synthesized systems.
The computational facet of our investigation, emphasized in this talk,
utilizes an open dissipative system approach, wherein a cumulant expansion
strategy is used to approximate the quantum Liouville equation via a
hierarchy of density operators. This has been successfully employed to
scrutinize partially coherent transport in protein/pigment complexes, but
here we focus on silicon quantum dot mesomaterials and use excited state
many-body calculations to populate the associated meta-Hamiltonian. After
an overview of the mesomaterial perspective, this talk will focus on our
computational assessment of the prospects for partially coherent exciton
transport through these silicon quantum dot mesomaterials.
--
Ryan Babbush | PhD Student in Physics
(949) 331-3943 | babbush(a)fas.harvard.edu
Harvard University | Aspuru-Guzik Group
12 Oxford Street | Cambridge, MA 02138
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