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.1 The electron nematicity has been recently observed in the iron-pnictide 2-6 and cuprate 7-9 hightemperature 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, 7-9 whilst in the iron-pnictides, it has been commonly associated with the tetragonalto-orthorhombic structural phase transition at T s . Here, we provide the first thermodynamic evidence in BaFe 2 (As 1−x P x ) 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.9,10 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 temperaturesone at T * , signifying a true nematic transition, and the other at T s (< T * ), 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.In the iron pnictides, the antiferromagnetic transition is closely intertwined with the structural phase transition from tetragonal (T) to orthorhombic (O) crystal symmetry. Although recent experiments, including neutron scattering, 2 ARPES, 3,11 STM, 4 and transport measurements, 5,6 have provided evidence for electronic anisotropy, these measurements were carried out either in the low-temperature orthorhombic phase, 2,4,11 where the crystal lattice structure has already broken C 4 symmetry, or in the tetragonal phase under uniaxial strain 3,5,6 that also breaks this symmetry. Therefore, the question remains open whether the electronic anisotropy can exist above the structural transition without an external driving force, including under the superconducting (SC) dome. In the past, the nematic transition in the pnictides has been associated either with the orbital ordering, [12][13][14][15][16][17][18] or with the spontaneous breaking of the Z 2 Ising symmetry between two collinear magnetic ordering wave-vectors Q = (π, 0) and (0, π).19-22 Therefore determining the nature of the nematicity is a key to understanding the microscopic origin of the lattice and magnetic...

Chemosensors detect a single target molecule from among several molecules, but cannot differentiate targets from one another. In this study, we report a molecular decoding strategy in which a single host domain accommodates a class of molecules and distinguishes between them with a corresponding readout. We synthesized the decoding host by embedding naphthalenediimide into the scaffold of an entangled porous framework that exhibited structural dynamics due to the dislocation of two chemically non-interconnected frameworks. An intense turn-on emission was observed on incorporation of a class of aromatic compounds, and the resulting luminescent colour was dependent on the chemical substituent of the aromatic guest. This unprecedented chemoresponsive, multicolour luminescence originates from an enhanced naphthalenediimide–aromatic guest interaction because of the induced-fit structural transformation of the entangled framework. We demonstrate that the cooperative structural transition in mesoscopic crystal domains results in a nonlinear sensor response to the guest concentration.