  The Landau spectrum of bismuth is complex and includes many angle-dependent
lines in the extreme quantum limit. The adequacy of single-particle theory to
describe this spectrum in detail has been an open issue. Here, we present a
study of angle-resolved Nernst effect in bismuth, which maps the angle-resolved
Landau spectrum for the entire solid angle up to 28 T. The experimental map is
in good agreement with the results of a theoretical model with parabolic
dispersion for holes and an extended Dirac Hamiltonian for electrons. The
angular dependence of additional lines in the Landau spectrum allows to uncover
the mystery of their origin. They correspond to the lines expected for the hole
Landau levels in a secondary crystal tilted by 108 degrees, the angle between
twinned crystals in bismuth. According to our results, the electron reservoirs
of the two identical tilted crystals have different chemical potentials and
carriers across the twin boundary have different concentrations. An exceptional
feature of this junction is that it separates two electron-hole compensated
reservoirs. The link between this edge singularity and the states wrapping a
three-dimensional electron gas in the quantum limit emerges as an outstanding
open question.
