  The Shastry-Sutherland compound SrCu$_2$(BO$_3$)$_2$ constituting
orthogonally coupled dimers harbors a $S=0$ singlet ground state. The
confluence of strong interdimer interaction and frustration engenders a
spectrum of low-energy excitations including localized triplons as well as
singlet and triplet bound states. Their dynamics are controlled by an external
magnetic field and temperature. Here, we employ high-field Raman spectroscopy
to map the field and temperature evolution of such bosonic composite
quasiparticles on approaching the 1/8 magnetization plateau. Our study unveils
that the magnetic field and thermal fluctuations show remarkably similar
effects in melting the singlet bound states, but are disparate in their effects
on the fine spectral shapes. This, together with the anti-crossing of two
singlet bound states in the intermediate field $B=10-16$ T, is discussed in
terms of the correlated dynamics of frustrated, interacting bosons.
