  Unconventional superconductors have been long sought for their potential
applications in quantum technologies and devices. A key challenge impeding this
effort is the difficulty associated with probing and characterizing candidate
materials and establishing their order parameter. In this Letter, we present a
platform that allows us to spectroscopically probe unconventional
superconductivity in thin-layer materials via the proximity effect. We show
that inducing an s-wave gap in a sample with an intrinsic d-wave instability
leads to the formation of bound-states of quasiparticle pairs, which manifest
as a collective mode in the d-wave channel. This finding provides a way to
study the underlying pairing interactions vicariously through the collective
mode spectrum of the system. Upon further cooling of the system we observe that
this mode softens considerably and may even condense, signaling the onset of
time-reversal symmetry breaking superconductivity. Therefore, our proposal also
allows for the creation and study of these elusive unconventional states.
