  HgCdTe alloys are unique because by increasing the Cd content x, one modifies
the band structure from inverted to normal, which fundamentally modifies the
dispersion of bulk and surface or edge (in the case of quantum wells) energy
states. Using alloys with x close to the concentration x_c at which the band
inversion transition is observed and with additional application of hydrostatic
pressure (p), one creates a favorable playground for studying the evolution of
Dirac matter and its topological properties. In this work, cryogenic
magnetospectroscopy in quantizing magnetic fields (B) at the far-infrared is
used to study inter-Landau-level transitions in high-quality HgCdTe MBE-grown
epitaxial layers with x ~ x_c as a function of p up to 4.2 kbar. Special
attention is paid to elucidate the role of the substrate and buffer layers,
which usually modify the pressure coefficients of epitaxial layers. For this
purpose, comparative measurements were carried out on as-grown epilayers with a
GaAs substrate and on free-standing layers obtained by etching off the
substrate. Spectra registered as a function of B (at given p) were analyzed
with the help of the Kane model modified to include magnetic field. The
pressure coefficient as well as the difference between conduction and valence
band deformation potentials of the free-standing layer were determined at 2 K.
Surprisingly, the deformation potentials and pressure coefficients of the
epitaxial layer and those of the free-standing layer differed by no more than
10 % in the pressure range up to 4.2 kbar. This finding questions the common
belief of a dominant influence of the substrate on the pressure coefficients of
epitaxial layers...
