33 research outputs found
Field-induced bound-state condensation and spin-nematic phase in SrCu(BO) revealed by neutron scattering up to 25.9 T
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(BO) , 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(BO) 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 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(BO) 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
Structure, spin correlations and magnetism of the square-lattice antiferromagnet SrCuTeWO ()
Quantum spin liquids are highly entangled magnetic states with exotic
properties. The square-lattice Heisenberg model is one of the
foundational models in frustrated magnetism with a predicted, but never
observed, quantum spin liquid state. Isostructural double perovskites
SrCuTeO and SrCuWO are physical realizations of this model, but
have distinctly different types magnetic order and interactions due to a
effect. Long-range magnetic order is suppressed in the solid
solution SrCuTeWO in a wide region of , where
the ground state has been proposed to be a disorder-induced spin liquid. Here
we show that the spin-liquid-like and samples have
distinctly different local spin correlations, which suggests they have
different ground states. Furthermore, the previously ignored interlayer
coupling between the square-planes is likely to play a role in the suppression
of magnetic order on the W-rich side at . These results
highlight the complex magnetism of SrCuTeWO and hint at a
new quantum critical point at .Comment: 19+8 pages, 6+8 figure
Structure, Spin Correlations, and Magnetism of the S = 1/2 Square-Lattice Antiferromagnet Sr2CuTe1-xWxO6 (0 ≤ x ≤ 1)
Quantum spin liquids are highly entangled magnetic states with exotic properties. The S = 1/2 square-lattice Heisenberg model is one of the foundational models in frustrated magnetism with a predicted, but never observed, quantum spin liquid state. Isostructural double perovskites Sr2CuTeO6 and Sr2CuWO6 are physical realizations of this model but have distinctly different types of magnetic order and interactions due to a d10/d0 effect. Long-range magnetic order is suppressed in the solid solution Sr2CuTe1-xWxO6 in a wide region of x = 0.05-0.6, where the ground state has been proposed to be a disorder-induced spin liquid. Here, we present a comprehensive neutron scattering study of this system. We show using polarized neutron scattering that the spin liquid-like x = 0.2 and x = 0.5 samples have distinctly different local spin correlations, which suggests that they have different ground states. Low-temperature neutron diffraction measurements of the magnetically ordered W-rich samples reveal magnetic phase separation, which suggests that the previously ignored interlayer coupling between the square planes plays a role in the suppression of magnetic order at x ≈ 0.6. These results highlight the complex magnetism of Sr2CuTe1-xWxO6 and hint at a new quantum critical point between 0.2 < x < 0.4.</p
High-field re-entrance of the magnetoelectric effect in LiNiPO<sub>4</sub> investigated in pulsed fields
Common and rare variant association analyses in amyotrophic lateral sclerosis identify 15 risk loci with distinct genetic architectures and neuron-specific biology
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with a lifetime risk of one in 350 people and an unmet need for disease-modifying therapies. We conducted a cross-ancestry genome-wide association study (GWAS) including 29,612 patients with ALS and 122,656 controls, which identified 15 risk loci. When combined with 8,953 individuals with whole-genome sequencing (6,538 patients, 2,415 controls) and a large cortex-derived expression quantitative trait locus (eQTL) dataset (MetaBrain), analyses revealed locus-specific genetic architectures in which we prioritized genes either through rare variants, short tandem repeats or regulatory effects. ALS-associated risk loci were shared with multiple traits within the neurodegenerative spectrum but with distinct enrichment patterns across brain regions and cell types. Of the environmental and lifestyle risk factors obtained from the literature, Mendelian randomization analyses indicated a causal role for high cholesterol levels. The combination of all ALS-associated signals reveals a role for perturbations in vesicle-mediated transport and autophagy and provides evidence for cell-autonomous disease initiation in glutamatergic neurons. A cross-ancestry genome-wide association meta-analysis of amyotrophic lateral sclerosis (ALS) including 29,612 patients with ALS and 122,656 controls identifies 15 risk loci with distinct genetic architectures and neuron-specific biology