Zone-Edge Lasing in Micro-Assembled Polaritonic Crystals
Long Zhang, Wei Xie, Jian Wang, Wenhui Liu, Dan Xu, Yinglei Wang, Jie Gu, Xuechu Shen, Zhanghai Chen
State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structure (Ministry of Education),
Department of Physics, Fudan University, Shanghai 200433, China
Abstract:
Band engineering in strongly coupled light-matter systems opens new horizons of photonics and crystal physics. ‘Polaritonic
crystal’ based on the half-light half-matter quasi-particles is expected to possess unique properties such as enhanced optical nonlinearity and
macroscopic quantum coherence, etc.. Here, we realize the room-temperature polaritonic crystals by simple micro-assembling. Folded
energy dispersion and band gap are revealed distinctly in the momentum space, which undoubtedly demonstrate the realization of
polaritonic crystal. Moreover, under intense excitation, condensate behavior appears at the edges of reduced Brillouin zones. The
corresponding periodical intensity distribution in real space demonstrates the condensation of meta-stable states in our system.
Experiment and Discussion
Figure 1  Illustration of the assembled polaritonic crystal based on ZnO-Si
microstructure. a, Schematic representation of the 1D polaritonic crystal. b,
Scanning electron microscope image (top-view) of a single ZnO microrod with
hexagonal cross section lying on a silicon slice with periodic structure. c,d, The
angle-resolved photoluminescence (PL) spectral (k-space) mapping under cw
excitation. c, Emission from a free standing ZnO microrod. d, Emission from
the same ZnO microwire lying on a silicon slice.
Figure 2  The energy band measured in momentum space demonstrating the formation of
polaritonic crystal. a, PL mapping (second derivative) in k-space under non-resonant excitation at
room temperature. Dashed curves display the calculated dispersion (mode N=105) with band gap (
 0.7 meV). b,c, Enlarged figures corresponding to the two regions labeled by white dashed rectangle
in (a) respectively, displaying the well-resolved energy gap induced by the anti-crossed dispersion.
Figure 3  the condensate behavior of polaritons in the nonlinear regime. a, The evolution
of polariton condensates in momentum space with the pumping power increasing. b,
Schematic picture for the polaritons condensate behavior in polaritonic crystal (the adjacent
two polariton modes are shown). c, The integrated intensities of polaritons A-state emission
as a function of pump power, corresponding to modes N=106 and N=105, respectively. The
intensity of these states shows obvious threshold behavior.
Conclusion
Figure 4  The real-space distribution of the polariton condensate. a, Schemetic
Bloch-wave functions for states labeled as A and A in Fig. 3a. b,c, Spatially resolved
PL mapping along the c-axis of the microrod with the modulation periods a=2 m
and a=4 m, respectively. d,e, Simulated intensity distribution of polariton
condensate at state
In summary, we have achieved 1D polaritonic crystals based on simply assembled ZnO-Si microstructure. Thanks to the
periodical potential introduced by the silicon grating, this artificial crystal exhibits folded dispersion of exciton-polariton and well resolved
band gaps at the edges of the MBZs at room temperature. Above the polariton condensate threshold, the polaritonic crystal shows strong
nonlinearity and massive polaritons accumulate at the meta-stable states. By using the spatially resolved micro-photoluminescence technique,
these unique condensates manifest themselves as the periodic emission patterns along the modulated direction of the rod. The results indicate
that the spatially modulated ZnO microcavity is an ideal candidate for the study of polariton superlattice physics.