Sterile neutrinos are a well-motivated objective of Beyond Standard Model searches. Extensions
to the Standard Model that include right-handed (sterile) neutrinos pose viable explanations for
the origin of neutrino masses, and they could also solve a variety of additional open questions in
physics, such as neutrino oscillation anomalies, the nature of dark matter, and baryon asymmetry.
Multiple models posit the existence of a GeV-scale sterile neutrino (also called heavy neutral
lepton), which can interact with the Standard Model particles through mixing. The heavy neutral
lepton can therefore be produced from, and decay into known particles. If the production from
up-scattering atmospheric neutrinos and the subsequent decay happen inside the IceCube detector,
it can produce a unique double-cascade signature. This signature can be utilized to search for
GeV-scale heavy neutral leptons at atmospheric neutrino energies. By focusing on the flux of
atmospheric muon neutrinos that oscillate into tau neutrinos, the less constrained tau-sterile mixing space can
be explored. We present an analysis approach to study heavy neutral leptons in the mass range
of 0.1 GeV-2 GeV, where we search for low-energy double-cascade topologies with the IceCube
DeepCore detector.