  Bose polarons are mobile impurities dressed by density fluctuations of a
surrounding degenerate Bose gas. These many-body objects have been realized in
ultracold atomic gasses and become a subject of intensive studies. In this
work, we show that excitons in electron-hole bilayers offer new opportunities
for exploring polarons in strongly interacting, highly tunable bosonic systems.
We found that Bose polarons are formed by spatially direct excitons immersed in
degenerate Bose gases of spatially indirect excitons (IXs). We detected both
attractive and repulsive Bose polarons by measuring photoluminescence
excitation spectra. We controlled the density of IX Bose gas by optical
excitation and observed an enhancement of the energy splitting between
attractive and repulsive Bose polarons with increasing IX density, in agreement
with our theoretical calculations.
