The pseudogap region of the phase diagram is an important unsolved puzzle in the field of high-transition-temperature (high-T(c)) superconductivity, characterized by anomalous physical properties. There are open questions about the number of distinct phases and the possible presence of a quantum-critical point underneath the superconducting dome. The picture has remained unclear because there has not been conclusive evidence for a new type of order. Neutron scattering measurements for YBa(2)Cu(3)O(6+delta) (YBCO) resulted in contradictory claims of no and weak magnetic order, and the interpretation of muon spin relaxation measurements on YBCO and of circularly polarized photoemission experiments on Bi(2)Sr(2)CaCu(2)O(8+delta)(refs 12, 13) has been controversial. Here we use polarized neutron diffraction to demonstrate for the model superconductor HgBa(2)CuO(4+delta) (Hg1201) that the characteristic temperature T* marks the onset of an unusual magnetic order. Together with recent results for YBCO, this observation constitutes a demonstration of the universal existence of such a state. The findings appear to rule out theories that regard T* as a crossover temperature rather than a phase transition temperature. Instead, they are consistent with a variant of previously proposed charge-current-loop order that involves apical oxygen orbitals, and with the notion that many of the unusual properties arise from the presence of a quantum-critical point.

Polarized beam neutron-scattering measurements on a highly perfect crystal of YBa 2 Cu 3 O 6.6 show a distinct magnetic transition to a different phase with an onset at about 235 K, the temperature expected for the pseudogap transition. The moment is found to be about 0.1 B for each sublattice and has a correlation length of at least 75 Å. We found the critical exponent for the magnetic neutron intensity to be 2␤ = 0.37Ϯ 0.12. This is the proper range for the class of transition that has no specific-heat divergence possibly explaining why none is found at the pseudogap transition.Superconductivity produces a gap in the quasiparticle spectrum which for conventional materials disappears as the temperature is increased to T c , where the superconducting electron pairs are no longer bound together. However, for the underdoped cuprate materials a pseudogap measured by a number of techniques appears at a temperature T ‫ء‬ Ͼ T c , with T ‫ء‬ increasing as T c gets smaller. This pseudogap associated with T ‫ء‬ is one of the most puzzling and important attributes of the cuprate superconductors. 1,2 Indeed since superconductivity originates from the pseudogap state, it is this state that has to be understood to determine the mechanism for hightemperature superconductivity. One possible origin of the pseudogap is to postulate that phase incoherent pairs are established as the material is cooled through the pseudogap temperature T ‫ء‬ , with superconductivity developing at a lower temperature T c when phase coherence is established. 3 This picture has been studied by the Nernst effect, 4 which shows the presence of vortexlike excitations in the pseudogap phase. However, upon warming the Nernst effect 4 disappears well before T ‫ء‬ is reached, suggesting that well-defined preformed pairs may not be present at temperatures as high as T ‫ء‬ .Completely different approaches 5-7 to the problem postulated a state with broken symmetry that displayed a pattern of circulating currents ͑CC phase͒ in the a-b plane. As the sample is cooled, this state appears at T ‫ء‬ and for near optimal doping ends at a quantum critical point. The present study considers a magnetic signal found at certain ͑H , K , L͒ positions in the reciprocal lattice. These would correspond to the phases considered by Varma 5,6 which preserve the translational symmetry of the lattice. Since translational symmetry is not broken, the signal to observe the phases occurs at the Bragg positions of the unit cell which means they sit on top of the much more intense nuclear scattering. A very sensitive polarized beam experiment is thus needed to observe them. Fauqué et al. 8 have undertaken polarized neutron-scattering measurements to search for this phase at the expected positions for several underdoped YBa 2 Cu 3 O 6+x ͑YBCO͒ samples. They observed an increase in polarized neutron scattering upon cooling, which represents a magnetic signal, which could be associated with the pseudogap temperature T ‫ء‬ . We have undertaken similar polarized neutron measurements on a well ...

(2008)], this establishes the universal existence of a genuine novel magnetic phase in underdoped cuprates with high maximal Tc (above 90 K at optimal doping). Here we report a systematic study of an underdoped Hg1201 sample (Tc = 75 K), the result of which is consistent with the previously established doping dependence of the magnetic signal. We present an assumption-free analysis of all the data available for Hg1201. Depending on how the hole concentration is estimated, comparison with the results for YBCO leads to different competition scenarios between the q = 0 magnetic order and the spin-density-wave order found in heavily underdoped YBCO.

The GALAXIES beamline at the SOLEIL synchrotron is dedicated to inelastic X-ray scattering (IXS) and photoelectron spectroscopy (HAXPES) in the 2.3-12 keV hard X-ray range. These two techniques offer powerful complementary methods of characterization of materials with bulk sensitivity, chemical and orbital selectivity, resonant enhancement and high resolving power. After a description of the beamline components and endstations, the beamline capabilities are demonstrated through a selection of recent works both in the solid and gas phases and using either IXS or HAXPES approaches. Prospects for studies on liquids are discussed.

In high-temperature copper oxide superconductors, a novel magnetic order associated with the pseudogap phase has been identified in two different cuprate families over a wide region of temperature and doping. We report here the observation below 120 K of a similar magnetic ordering in the archetypal cuprate La(2-x)Sr(x)CuO4 (LSCO) system for x=0.085. In contrast with the previous reports, the magnetic ordering in LSCO is only short range with an in-plane correlation length of ∼10  A and is bidimensional (2D). Such a less pronounced order suggests an interaction with other electronic instabilities. In particular, LSCO also exhibits a strong tendency towards stripes ordering at the expense of the superconducting state.

The elucidation of the pseudogap phenomenon of the cuprates, a set of anomalous physical properties below the characteristic temperature T * and above the superconducting transition temperature T c , has been a major challenge in condensed matter physics for the past two decades [1]. Following initial indications of broken time-reversal symmetry in photoemission experiments [2], recent polarized neutron diffraction work demonstrated the universal existence of an unusual magnetic order below T * [3,4]. These findings have the profound implication that the pseudogap regime constitutes a genuine new phase of matter rather than a mere crossover phenomenon. They are furthermore consistent with a particular type of order involving circulating orbital currents, and with the notion that the phase diagram is controlled by a quantum critical point [5]. Here we report inelastic neutron scattering results for HgBa 2 CuO 4+δ (Hg1201) that reveal a fundamental collective magnetic mode associated with the unusual order, and that further support this picture. The mode's intensity rises below the same temperature T * and its dispersion is weak, as expected for an Ising-like order parameter [6]. Its energy of 52-56 meV and its enormous integrated spectral weight render it a new candidate for the hitherto unexplained ubiquitous electron-boson coupling features observed in spectroscopic studies [7][8][9][10].Inelastic neutron scattering (INS) is the most direct probe of magnetic excitations in solids. In the present work, we employed both spin-polarized and unpolarized INS measurements. The use of spin-polarized neutrons was crucial to unambiguously identify the magnetic response reported here, because such neutrons are separately collected according to whether their spins have or have not been flipped in the scattering process, which renders magnetic and nuclear scattering clearly distinguishable (Supplementary Information Section 1). Our measurements were carried out on three samples made of co-aligned crystals, which were grown by a self-flux method [11] and free from substantial macroscopic impurity phases and inhomogeneity (SI Section 2). Hg1201 exhibits the highest value of T c of all cuprates with one copper-oxygen plane per unit cell, has a simple tetragonal structure, and is furthermore thought to be relatively free of disorder effects [12,13]. The scattering wave vector is quoted as Q = Ha* + Kb* + Lc* ≡ (H,K,L) in reciprocal lattice units (r.l.u.). Neutron intensities are presented in normalized units in most figures to facilitate a direct comparison of the intensity among the measurements (SI Section 3).Spin-polarized INS data ( Fig. 1) demonstrate the existence of a magnetic excitation throughout the two-dimensional (2D) Brillouin zone in a nearly-optimally-doped sample (T c = 94.5 ± 2 K, denoted as OP95). Energy scans in the spin-flip channel reveal a resolution-limited feature at low temperatures, with a weak dispersion and a maximum of 56 meV at the 2D zone-corner q AF (H = K = 0.5). The feature cannot be due to a p...