  Ultra-hot Jupiters (UHJs) possess the most extreme environments among various
types of exoplanets, making them ideal laboratories to study the chemical
composition and kinetics properties of exoplanet atmosphere with
high-resolution spectroscopy (HRS). It has the advantage of resolving the tiny
Doppler shift and weak signal from exoplanet atmosphere and has helped to
detect dozens of heavy elements in UHJs including KELT-9b, WASP-76b, WASP-121b.
MASCARA-4b is a 2.8-day UHJ with an equilibrium temperature of $\sim2250$ K,
which is expected to contain heavy elements detectable with VLT. In this
letter, we present a survey of atoms/ions in the atmosphere of the MASCARA-4b,
using the two VLT/ESPRESSO transits data. Cross-correlation analyses are
performed on the obtained transmission spectra at each exposure with the
template spectra generated by petitRADTRANS for atoms/ions from element Li to
U. We confirm the previous detection of Mg, Ca, Cr and Fe and report the
detection of Rb, Sm, Ti+ and Ba+ with peak signal-to-noise ratios (SNRs) $>$ 5.
We report a tentative detection of Sc+, with peak SNRs $\sim$6 but deviating
from the estimated position. The most interesting discovery is the first-time
detection of elements Rb and Sm in an exoplanet. Rb is an alkaline element like
Na and K, while Sm is the first lanthanide series element and is by far the
heaviest one detected in exoplanets. Detailed modeling and acquiring more data
are required to yield abundance ratios of the heavy elements and to understand
better the common presence of them in UHJ's atmospheres.
