  Strongly interacting electrons can exhibit novel collective phases, among
which the electronic nematic phases are perhaps the most surprising as they
spontaneously break rotational symmetry of the underlying crystal lattice. The
electron nematicity has been recently observed in the iron-pnictide and cuprate
high-temperature superconductors. Whether such a tendency of electrons to
self-organise unidirectionally has a common feature in these superconductors
is, however, a highly controversial issue. In the cuprates, the nematicity has
been suggested as a possible source of the pseudogap phase, whilst in the
iron-pnictides, it has been commonly associated with the
tetragonal-to-orthorhombic structural phase transition at $T_s$. Here, we
provide the first thermodynamic evidence in BaFe2(As1-xPx)2 that the nematicity
develops well above the structural transition and persists to the nonmagnetic
superconducting regime, resulting in a new phase diagram strikingly similar to
the pseudogap phase diagram in the cuprates. Our highly sensitive magnetic
anisotropy measurements using microcantilever torque-magnetometry under
in-plane field rotation reveal pronounced two-fold oscillations, which break
the tetragonal symmetry. Combined with complementary high-resolution
synchrotron X-ray and resistivity measurements, our results consistently
identify two distinct temperatures - one at $T^{\ast}$, signifying a true
nematic transition, and the other at $T_s (< T^{\ast})$, which we show to be
not a true phase transition, but rather what we refer to as a "meta-nematic
transition", in analogy to the well-known metamagnetic transition in the theory
of magnetism. Our observation of the extended nematic phase above the
superconducting dome establishes that the nematicity has primarily an
electronic origin, inherent in the normal state of high-temperature
superconductors.
