  Aims. Moreno-Insertis et al. (2018) recently discovered two types of flux
emergence in their numerical simulations: magnetic loops and magnetic sheet
emergence. Whereas magnetic loop emergence has been documented well in the last
years, by utilising high-resolution full Stokes data from ground-based
telescopes as well as satellites, magnetic sheet emergence is still an
understudied process. We report here on the first clear observational evidence
of a magnetic sheet emergence and characterise its development.
  Methods. Full Stokes spectra from the Hinode spectropolarimeter were inverted
with the SIR code to obtain solar atmospheric parameters such as temperature,
line-of-sight velocities and full magnetic field vector information.
  Results. We analyse a magnetic flux emergence event observed in the quiet-sun
internetwork. After a large scale appearance of linear polarisation, a magnetic
sheet with horizontal magnetic flux density of up to 194 Mx/cm$^{2}$ hovers in
the low photosphere spanning a region of 2 to 3 arcsec. The magnetic field
azimuth obtained through Stokes inversions clearly shows an organised structure
of transversal magnetic flux density emerging. The granule below the magnetic
flux-sheet tears the structure apart leaving the emerged flux to form several
magnetic loops at the edges of the granule.
  Conclusions. A large amount of flux with strong horizontal magnetic fields
surfaces through the interplay of buried magnetic flux and convective motions.
The magnetic flux emerges within 10 minutes and we find a longitudinal magnetic
flux at the foot points of the order of $\sim$$10^{18}$ Mx. This is one to two
orders of magnitude larger than what has been reported for small-scale magnetic
loops. The convective flows feed the newly emerged flux into the pre-existing
magnetic population on a granular scale.
