  We analyse the transmission spectra of KELT-20b/MASCARA-2b to search for
possible thermal inversion agents. The data consist of three transits obtained
using HARPSN and one using CARMENES. We removed stellar and telluric lines
before cross-correlating the residuals with spectroscopic templates produced
using a 1D plane-parallel model assuming an isothermal atmosphere and chemical
equilibrium at solar metallicity. Using a likelihood-mapping method, we detect
Fe\,{\sc i} at $>$ 13-$\sigma$, Ca\,{\sc ii} H$\&$K at $>$ 6-$\sigma$ and
confirm the previous detections of Fe\,{\sc ii}, Ca\,{\sc ii} IRT and Na\,{\sc
i} D. The detected signal of Fe\,{\sc i} is shifted by -3.4$\pm$0.4 km s$^{-1}$
from the planetary rest frame, which indicates a strong day-night wind. Our
likelihood-mapping technique also reveals that the absorption features of the
detected species extend to different altitudes in the planet's atmosphere.
Assuming that the line lists are accurate, we do not detect other potential
thermal inversion agents (NaH, MgH, AlO, SH, CaO, VO, FeH and TiO) suggesting
that non-chemical equilibrium mechanisms (e.g. a cold-trap) might have removed
Ti- and V-bearing species from the upper atmosphere. Our results, therefore,
shows that KELT-20b/MASCARA-2b cannot possess an inversion layer caused by a
TiO/VO-related mechanism. The presence of an inversion layer would therefore
likely be caused by metal atoms such as Fe\,{\sc i} and Fe\,{\sc ii}. Finally,
we report a double-peak structure in the Fe\,{\sc i} signal in all of our
data-sets that could be a signature of atmospheric dynamics. However, further
investigation is needed to robustly determine the origin of the signal.
