A recent addition to low-dimensional materials are monolayer
transition metal dichalcogenides
(TMDs), such as WSe2, with an atomically thin, honeycomb lattice and
optical band gaps. In
addition to spin, charge carriers in TMDs exhibit a “valley” degree of
freedom, which can be
optically addressed using circularly polarized light, opening up exciting
“valleytronics". Another curious aspect of TMDs lies in the non-trivial
geometry of their band
structure which gives rise to equal but opposite Berry curvature, an
effective magnetic field in
the momentum space. Owing to unusually strong Coulomb interactions in
truly 2D limit, optical
spectra of monolayer TMDs is dominated by tightly bound excitons that are
expected to strongly
couple to light and form stable polaritons - half light, half matter
In this talk, I will begin by presenting our recent results on valley
Zeeman effect, where in
analogy to spins, valleys shift in energy with magnetic field. Next, I
will discuss our theoretical
results on how the non-trivial geometry of Bloch bands modifies the
excitonic fine structure of
TMDs resulting in an orbital Zeeman effect in reciprocal space and a
Lamb-like shift of levels.
Finally, I will present our recent results on the observation of
microcavity polaritons confirming
the strong light-matter interactions in these materials. The presence of
valley degree of freedom,
non-trivial geometry of bands, and the possibility of introducing
non-linearities in form of
quantum emitters makes polaritons in TMDs particularly appealing for
many-body physics and topological states of matter.
Dr. Ajit Srivastava is a physicist working in the field of light-matter
at nanoscale with a special focus on the role of geometry and topology in
solid-state. He is an Assistant Professor in the Department of Physics at
University, Atlanta, USA.
He completed his Bachelors degree from Indian Institute of Technology,
and subsequently he obtained Masters degree from Rice University in 2003.
a PhD degree in Applied Physics from the Solid State Optical Spectroscopy
Rice University in 2008. He worked as Postdoctoral Fellow (2009-2013) and
later as a
Senior Scientist (2013-2015) in Professor Atac Imamoglu’s Quantum
Photonics Group at
the Institute of Quantum Electronics, ETH Zurich, where he was one of the
person working on 2D materials. In 2016, he was appointed as Assistant
Emory University where he now runs the Quantum Light-Matter Lab.
Dr. Srivastava’s expertise in quantum optics, strong light-matter interactions, physics of atomically thin 2D materials, role of geometry and topology in low-dimensions, Berry phase and artificial gauge fields.