Title: Valley polarized relaxation and upconversion luminescence from Tamm-Plasmon Trion-Polaritons with a MoSe2 monolayer,
Abstract: Transition metal dichalcogenides represent an ideal testbed to study
excitonic effects, spin-related phenomena and fundamental light-matter coupling
in nanoscopic condensed matter systems. In particular, the valley degree of
freedom, which is unique to such direct band gap monolayers with broken
inversion symmetry, adds fundamental interest in these materials. Here, we
implement a Tamm-plasmon structure with an embedded MoSe2 monolayer and study
the formation of polaritonic quasi-particles. Strong coupling conditions
between the Tamm-mode and the trion resonance of MoSe2 are established,
yielding bright luminescence from the polaritonic ground state under
non-resonant optical excitation. We demonstrate, that tailoring the
electrodynamic environment of the monolayer results in a significantly
increased valley polarization. This enhancement can be related to change in
recombination dynamics shown in time-resolved photoluminescence measurements.
We furthermore observe strong upconversion luminescence from resonantly excited
polariton states in the lower polariton branch. This upconverted polariton
luminescence is shown to preserve the valley polarization of the
trion-polariton, which paves the way towards combining spin-valley physics and
exciton scattering experiments.