Superconductivity in cuprates emerges out of a complex normal state that hosts density waves, pseudogap physics, and strange metal properties. Here, we access this normal state by synchronizing free-electron laser x-rays with high-magnetic-field pulses up to 44 T. We observe a linear increase in charge order amplitude and correlation length that persists far above the vortex melting transition. This behavior is incompatible with standard phase competition between charge order and superconductivity. By means of conventional hard x-ray diffraction and magnetostriction, we show that applied fields also enhance monoclinic lattice distortions. However, this magnetoelastic response is weaker and an epiphenomenon of the stripe order enhancement. Combined with recent observations of field-linear spin freezing, our results point to a direct coupling between magnetic field and the spin component of stripe order in the high-field normal state – a mechanism independent of superconductivity suppression that has so far remained hidden from scattering probes.

The magnetic structure of a magnetic topological semimetal EuMnSb_2 is investigated in fields up to 30 T using polarized and unpolarized neutron diffraction, pulsed-field x-ray magnetic circular dichroism and pulsed-field magnetometry. We determine the zero-field magnetic structures of the Eu and Mn sublattices, and find that magnetic transitions induced by applied fields below 2 T correspond to changes in the magnetic order of the Eu spins alone without detectable perturbation to the order of the Mn spins. An additional magnetic transition is observed at fields close to the saturation field for the Eu spins. We present a mean-field model which describes key features of the magnetic behavior and allows us to estimate the dominant Eu–Eu and Eu–Mn exchange interactions responsible for the coupling between magnetism and electronic topology.

The simultaneous application of high magnetic fields and high pressures for controlling magnetic ground states is important for testing our understanding of many-body quantum theory. However, the implementation for neutron scattering experiments presents a technical challenge. To overcome this challenge we present an optimized pressure-cell design with a novel bullet shape, which is compatible with horizontal-field magnets, in particular the high-field magnet operating at the Helmholtz-Zentrum Berlin. The cell enabled neutron diffraction and spectroscopy measurements with the combination of three extreme conditions: high pressures, high magnetic fields, and dilution temperatures, simultaneously reaching 0.7 GPa, 25.9 T, and 200 mK. Our results demonstrate the utility of informed material choices and the efficiency of finite-element analysis for future pressure-cell designs to be used in combination with magnetic fields and dilution temperatures for neutron scattering purposes.

In quantum magnetic materials, ordered phases induced by an applied magnetic field can be described as the Bose-Einstein condensation (BEC) of magnon excitations. In the strongly frustrated system SrCu2(BO3)(2), no clear magnon BEC could be observed, pointing to an alternative mechanism, but the high fields required to probe this physics have remained a barrier to detailed investigation. Here we exploit the first purpose-built high-field neutron scattering facility to measure the spin excitations of SrCu2(BO3)(2) up to 25.9 T and use cylinder matrix-product-states (MPS) calculations to reproduce the experimental spectra with high accuracy. Multiple unconventional features point to a condensation of S = 2 bound states into a spin-nematic phase, including the gradients of the one-magnon branches and the persistence of a one-magnon spin gap. This gap reflects a direct analogy with superconductivity, suggesting that the spin-nematic phase in SrCu2(BO3)(2) is best understood as a condensate of bosonic Cooper pairs.

The extremely overdoped cuprates are generally considered to be Fermi liquid metals without exotic orders, whereas the underdoped cuprates harbor intertwined states. Contrary to this conventional wisdom, using Cu L-3-edge and O K-edge resonant x-ray scattering, we reveal a charge order (CO) correlation in overdoped La2-xSrxCuO4 (0.35 <= x <= 0.6) beyond the superconducting dome. This CO has a periodicity of -6 lattice units with correlation lengths of similar to 20 lattice units. It shows similar in-plane momentum and polarization dependence and dispersive excitations as the CO of underdoped cuprates, but its maximum intensity differs along the c direction and persists up to 300 K. This CO correlation cannot be explained by the Fermi surface instability and its origin remains to be understood. Our results suggest that CO is prevailing in the overdoped metallic regime and requires a reassessment of the picture of overdoped cuprates as weakly correlated Fermi liquids.

The extremely overdoped cuprates are generally considered to be Fermi liquid metals without exotic orders, whereas the underdoped cuprates harbor intertwined states. Contrary to this conventional wisdom, using Cu L-3-edge and O K-edge resonant x-ray scattering, we reveal a charge order (CO) correlation in overdoped La2-xSrxCuO4 (0.35 <= x <= 0.6) beyond the superconducting dome. This CO has a periodicity of similar to 6 lattice units with correlation lengths of similar to 20 lattice units. It shows similar in-plane momentum and polarization dependence and dispersive excitations as the CO of underdoped cuprates, but its maximum intensity differs along the c direction and persists up to 300 K. This CO correlation cannot be explained by the Fermi surface instability and its origin remains to be understood. Our results suggest that CO is prevailing in the overdoped metallic regime and requires a reassessment of the picture of overdoped cuprates as weakly correlated Fermi liquids.

Bose-Einstein condensation (BEC) underpins exotic forms of order ranging from superconductivity to superfluid 4 He. In quantum magnetic materials, ordered phases induced by an applied magnetic field can be described as the BEC of magnon excitations. With sufficiently strong magnetic frustration, exemplified by the system SrCu$_2$(BO$_3$)$_2$ , no clear magnon BEC is observed and the complex spectrum of multi-magnon bound states may allow a different type of condensation, but the high fields required to probe this physics have remained a barrier to detailed investigation. Here we exploit the first purpose-built high-field neutron scattering facility to measure the spin excitations of SrCu$_2$(BO$_3$)$_2$ up to 25.9 T and use cylinder matrix-product-states (MPS) calculations to reproduce the experimental spectra with high accuracy. Multiple unconventional features point to a condensation of $S = 2$ bound states into a spin-nematic phase, including the gradients of the one-magnon branches, the presence of many novel composite two- and three-triplon excitations and the persistence of a one-magnon spin gap. This gap reflects a direct analogy with superconductivity, suggesting that the spin-nematic phase in SrCu$_2$(BO$_3$)$_2$ is best understood as a condensate of bosonic Cooper pairs. Our results underline the wealth of unconventional states yet to be found in frustrated quantum magnetic materials under extreme conditions.

Bragg diffracted intensities and q values for crystalline structures with long repeat distances may be obtained by small-angle neutron scattering (SANS) investigations. An account is given of the methods, advantages and disadvantages of obtaining such data by the multichromatic time-of-flight method, compared with the more traditional quasi-monochromatic SANS method. This is illustrated with data obtained from high-magnetic-field measurements on magnetic vortex line lattices in superconductors on the former HFM/EXED instrument at Helmholtz-Zentrum Berlin. The methods have application to other mesoscopic crystalline structures investigated by SANS instruments at pulsed sources.

Complex bound states of magnetic excitations, known as Bethe string, were predicted almost a century ago to exist in one-dimensional quantum magnets 1. The dispersions of the string states have so far remained the subject of intensive theoretical studies 2-7. By performing neutron scattering experiments on the one-dimensional Heisenberg-Ising antiferromagnet SrCo2V2O8 in high longitudinal magnetic fields, we reveal in detail the dispersion relations of the string states over the full Brillouin zone, as well as their magnetic field dependences. Furthermore the characteristic energy, the scattering intensity and linewidth of the observed string states exhibit excellent agreement with our precise Bethe Ansatz calculations. Our results establish the important role of string states in the quantum spin dynamics of one-dimensional systems, and will invoke studies of their dynamical properties in more general many-body systems.

Ellen Fogh ,1,2,* Takumi Kihara,3 Rasmus Toft-Petersen ,1 Maciej Bartkowiak ,4 Yasuo Narumi,3 Oleksandr Prokhnenko,4 Atsushi Miyake,5 Masashi Tokunaga,5 Kenichi Oikawa ,6 Michael Korning Sørensen ,1 Julia Cathrine Dyrnum,1 Hans Grimmer ,7 Hiroyuki Nojiri,3 and Niels Bech Christensen1 1Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark 2Laboratory for Quantum Magnetism, Institute of Physics, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland 3Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan 4Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany 5The Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan 6Materials and Life Science Division, J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan 7Research with Neutrons and Muons, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland

The Extreme Environment Diffractometer was a neutron time-of-flight instrument equipped with a constant-field hybrid magnet providing magnetic fields up to 26 T. The magnet infrastructure and sample environment imposed limitations on the geometry of the experiment, making it necessary to plan the experiment with care. EXEQ is the software tool developed to allow users of the instrument to find the optimal sample orientation for their diffraction experiment. InEXEQ fulfilled the same role for the inelastic neutron scattering experiments. The source code of the software is licensed under the GNU General Public Licence 3, allowing it to be used by other facilities and adapted for use on other instruments.

Neutron diffraction with static and pulsed magnetic fields is used to directly probe the magnetic structures in LiNiPO4 up to 25 T and 42 T, respectively. By combining these results with magnetometry and electric polarization measurements under pulsed fields, the magnetic and magnetoelectric phases are investigated up to 56 T applied along the easy c axis. In addition to the already known transitions at lower fields, three new ones are reported at 37.6, 39.4, and 54 T. Ordering vectors are identified with Q(VI) = (0, 1/3, 0) in the interval 37.6 - 39.4 T and Q(VII) = (0, 0, 0) in the interval 39.4 - 54 T. A quadratic magnetoelectric effect is discovered in the Q(VII) = (0, 0, 0) phase and the field dependence of the induced electric polarization is described using a simple mean-field model. The observed magnetic structure and magnetoelectric tensor elements point to a change in the lattice symmetry in this phase. We speculate on the possible physical mechanism responsible for the magnetoelectric effect in LiNiPO4.

The adsorption of water in one-dimensional channels in porous aluminophosphate material AlPO4-5 has been studied by a combination of gravimetric analysis techniques, neutron and X-ray diffraction and neutron spectroscopy. Molecular structure of AlPO4-5 consists of 12-membered rings of alternating, corner-sharing AlO4 and PO4 tetrahedra connected by oxygen bridges into sheets in the (a, b) plane. The sheets are connected by oxygen bridges along the c crystal axis and form one-dimensional channels of which the largest, formed by the 12-membered rings, have a van der Waals diameter of about 8.3 angstrom. Gradually increasing the amount of adsorbed water we could follow the evolution of the confined water mobility in a systematic way and identify the molecular mechanism of water adsorption. We focused particularly on the range of low and medium relative pressures up to p/p(0) = 0.32, where a change from a hydrophobic behavior to a steep, capillary condensation like water intake has been observed. At the initial adsorption stages water occupies positions close to the pore walls causing the contraction of channels in the (a, b) plane and the prolongation of the channels along c axis in AlPO4-5. With the progressing intake water molecules form chains along the main channels. The cooperative interactions between water molecules lead to the onset of phonon-like cooperative modes and, surprisingly, to the increase of diffusive-like motion, which slow down only in the final adsorption stages when AlPO4-5 channels are completely filled.

A detailed diffraction study of Ca10Cr7O28 is presented which adds significant new insights into the structural and magnetic properties of this compound. A new crystal structure type was used where the a and b axes are doubled compared to previous models providing a more plausible structure where all crystallographic sites are fully occupied. The presence of two different valences of chromium was verified and the locations of the magnetic Cr5+ and non-magnetic Cr6+ ions were identified. The Cr5+ ions have spin-12 and form distorted kagome bilayers which are stacked in an ABC arrangement along the c axis. These results lay the foundation for understanding of the quantum spin liquid behavior in Ca10Cr7O28 which has recently been reported in Balz et al (2016 Nat. Phys. 12 942).

An overview of the high magnetic field facility for neutron scattering at Helmholtz Zentrum Berlin (HZB) is given. The facility enables elastic and inelastic neutron scattering experiments in continuous magnetic fields up to 26.3 T combined with temperatures down to 0.6 K.

The magnetic phase diagram of magnetoelectric LiCoPO4 is established using neutron diffraction and magnetometry in fields up to 25.9 T applied along the crystallographic b axis. For fields greater than 11.9 T, the magnetic unit cell triples in size with propagation vector Q = (0, 1/3,0). A magnetized elliptic cycloid is formed with spins in the (b, c) plane and the major axis oriented along b. Such a structure allows for the magnetoelectric effect with an electric polarization along c induced by magnetic fields applied along b. Intriguingly, additional ordering vectors Q approximate to (0, 1/4,0) and Q approximate to (0, 1/2,0) appear for increasing fields in the hysteresis region below the transition field. Traces of this behavior are also observed in the magnetization. A simple model based on a mean-field approach is proposed to explain these additional ordering vectors. In the field interval 20.5-21.0 T, the propagation vectorQ = (0, 1/3,0) remains but the spins orient differently compared to the cycloid phase. Above 21.0 T and up until saturation, a commensurate magnetic structure exists with a ferromagnetic component along b and an antiferromagnetic component along c.

Helmholtz-Zentrum Berlin (HZB) operates the medium flux research reactor BER II and the third generation synchrotron source BESSY II.HZB is known for providing an outstanding sample environment, especially high magnetic fields and low temperatures, which is available for both internal and external users.In this contribution we present the latest achievement in this field -High Magnetic Field Facility for Neutron Scattering, which was recently launched at HZB.This facility allows combining neutron scattering with continuous magnetic fields as high as 26 T and temperatures down to 0.65 K (at present) and 0.1 K (in near future).The application of high magnetic fields is a powerful method for revealing the complex behavior in modern materials.In combination with microscopic probe such as neutrons it provides a direct access to static and dynamic correlations in matter.Recently HZB in collaboration with the National High Magnetic Field Laboratory (USA) built a unique horizontal solenoid High Field Magnet (HFM) [1].The magnet utilizes hybrid (resistive insert and superconducting outsert) technology and reaches 26 T at full power of 4 MW.The tapered inner coil allows neutron-scattering to detectors up to +/-15° off the beam axis.Furthermore the magnet can be rotated by an additional 15° to access a larger reciprocal space region.Neutron scattering in high fields is performed using the dedicated Extreme Environment Diffractometer (EXED) [2].EXED uses time-of-flight (TOF) polychromatic technique which compensates very limited angular access available in the HFM.TOF technique combined with 15° magnet rotation provides a gapless coverage of Q-range from 0.1 up to 12 Å-1 for diffraction experiments.The low-Q range can be extended beyond 10-2 Å-1 using a pin-hole TOF Small Angle Scattering mode implemented on the instrument.In addition to the existing elastic capabilities, a direct TOF spectrometer mode was built in this year.The latter will enable inelastic neutron scattering experiments over a limited Q-range < 1.8 Å-1 with an energy resolution of a few percent and incident energies below 25 meV [3].Since the magnet has room temperature bore, several low-temperature inserts have been developed at HZB.They include 4He-cryostat (1.5 K) with a sample rotation stage, 3He cryostat (0.65 K) and a dilution fridge (0.1 K, in fabrication).In this contribution the overview and capabilities of the HFM-EXED facility will be presented together with the selected experimental results.

Helmholtz-Zentrum Berlin (HZB) operates two large-scale facilities: the research reactor BER 2 and the synchrotron source for soft X-rays BESSY 2. This year HZB's neutron instrument suite around BER 2 has been strengthened by a unique high-magnetic-field facility for neutron scattering. Its main components are the High Field Magnet (HFM), which is the most powerful dc magnet for neutron scattering worldwide, and the Extreme Environment Diffractometer (EXED), which is a dedicated neutron instrument for time-of-flight technique. The hybrid magnet system is projected according to the special geometric constraints of analyzing samples by neutron scattering in a high field magnet. Following our past experience, only steady-state fields are adequate to achieve the goals of the project. In particular, inelastic scattering studies would virtually be excluded when using pulsed magnets. The new series-connected hybrid magnet with a horizontal field orientation was designed and constructed in collaboration with the National High Magnetic Field Laboratory (NHMFL), Tallahassee, FL, USA. With a set consisting of a superconducting cable-in-conduit coil and different resistive coils of conical shape, maximum fields between 26-31 T are possible with cooling power between 4 and 8 MW for the resistive part. A series of commissioning activities of the magnet components and the technical infrastructure systems (20-kA power supply, water cooling, and 4-K Helium refrigerator) was completed at HZB. The maximum field achieved with a 4-MW resistive coil was 26 T.