  The fractional quantum Hall state (FQHS) observed at a half-filled Landau
level in an interacting two-dimensional electron system (2DES) is among the
most exotic states of matter as its quasiparticles are expected to be Majoranas
with non-Abelian statistics. We demonstrate here the unexpected presence of
such a state in a novel 2DES with a strong band-mass anisotropy. The FQHS we
observe has unusual characteristics. While its Hall resistance is
well-quantized at low temperatures, it exhibits highly-anisotropic in-plane
transport resembling compressible stripe/nematic charge-density-wave phases.
More striking, the anisotropy sets in suddenly below a critical temperature,
suggesting a finite-temperature phase transition. Our observations highlight
how anisotropy modifies the many-body phases of a 2DES, and should further fuel
the discussion surrounding the enigmatic even-denominator FQHS.
