191 research outputs found
Spin wave Hamiltonian and anomalous scattering in NiPS
We report a comprehensive spin wave analysis of the semiconducting honeycomb
van der Waal antiferromagnet NiPS. Using single crystal inelastic neutron
scattering, we map out the full Brillouin zone and fit the observed modes to a
spin wave model with rigorously defined uncertainty. We find that the third
neighbor exchange dominates the Hamiltonian, a feature which we fully
account for by ab-initio density functional theory calculations. We also
quantify the degree to which the three-fold rotation symmetry is broken and
account for the excitations observed in other measurements, yielding a
spin exchange model which is consistent across multiple experimental probes. We
also identify a strongly reduced static ordered moment and reduced low-energy
intensity relative to the linear spin wave calculations, signaling unexplained
features in the magnetism which requires going beyond the linear spin wave
approximation.Comment: 7 pages, 8 figures; 5 pages and 6 additional figures of appendice
Hidden low-temperature magnetic order revealed through magnetotransport in monolayer CrSBr
Magnetic semiconductors are a powerful platform for understanding, utilizing
and tuning the interplay between magnetic order and electronic transport.
Compared to bulk crystals, two-dimensional magnetic semiconductors have greater
tunability, as illustrated by the gate modulation of magnetism in exfoliated
CrI and CrGeTe, but their electrically insulating properties
limit their utility in devices. Here we report the simultaneous electrostatic
and magnetic control of electronic transport in atomically-thin CrSBr, an
A-type antiferromagnetic semiconductor. Through magnetotransport measurements,
we find that spin-flip scattering from the interlayer antiferromagnetic
configuration of multilayer flakes results in giant negative magnetoresistance.
Conversely, magnetoresistance of the ferromagnetic monolayer CrSBr vanishes
below the Curie temperature. A second transition ascribed to the ferromagnetic
ordering of magnetic defects manifests in a large positive magnetoresistance in
the monolayer and a sudden increase of the bulk magnetic susceptibility. We
demonstrate this magnetoresistance is tunable with an electrostatic gate,
revealing that the ferromagnetic coupling of defects is carrier mediated
Brain tumour diagnostics using a DNA methylation-based classifier as a diagnostic support tool
Aims: Methylation profiling (MP) is increasingly incorporated in the diagnostic process of central nervous system (CNS) tumours at our centres in The Netherlands and Scandinavia. We aimed to identify the benefits and challenges of MP as a support tool for CNS tumour diagnostics. Methods: About 502 CNS tumour samples were analysed using (850 k) MP. Profiles were matched with the DKFZ/Heidelberg CNS Tumour Classifier. For each case, the final pathological diagnosis was compared to the diagnosis before MP. Results: In 54.4% (273/502) of all analysed cases, the suggested methylation class (calibrated score ≥0.9) corresponded with the initial pathological diagnosis. The diagnosis of 24.5% of these cases (67/273) was more refined after incorporation of the MP result. In 9.8% of cases (49/502), the MP result led to a new diagnosis, resulting in an altered WHO grade in 71.4% of these cases (35/49). In 1% of cases (5/502), the suggested class based on MP was initially disregarded/interpreted as misleading, but in retrospect, the MP result predicted the right diagnosis for three of these cases. In six cases, the suggested class was interpreted as ‘discrepant but noncontributory’. The remaining 33.7% of cases (169/502) had a calibrated score <0.9, including 7.8% (39/502) for which no class indication was given at all (calibrated score <0.3). Conclusions: MP is a powerful tool to confirm and fine-tune the pathological diagnosis of CNS tumours, and to avoid misdiagnoses. However, it is crucial to interpret the results in the context of clinical, radiological, histopathological and other molecular information
Non-linear magnons and exchange Hamiltonians of delafossite proximate quantum spin liquids
Quantum spin liquids (QSL) are theoretical states of matter with long-range
entanglement and exotic quasiparticles. However, they generally elude
quantitative theory, rendering their underlying phases mysterious and hampering
efforts to identify experimental QSL states. Here we study triangular lattice
resonating valence bond QSL candidate materials KYbSe and NaYbSe. We
measure the magnon modes in their 1/3 plateau phase, where quantitative theory
is tractable, using inelastic neutron scattering and fit them using nonlinear
spin wave theory. We also fit the KYbSe heat capacity using high
temperature series expansion. Both KYbSe fits yield the same magnetic
Hamiltonian to within uncertainty, confirming previous estimates and showing
the Heisenberg to be an accurate model for these materials. Most
importantly, comparing KYbSe and NaYbSe shows that smaller -site
Na ion has a larger ratio. However, hydrostatic pressure applied
to KYbSe increases the ordering temperature (a result consistent with
density functional theory calculations), indicating that pressure decreases
. These results show how periodic table and hydrostatic pressure can
tune the YbSe materials in a controlled way.Comment: 7 pages, 7 figures; 4 pages and 7 additional figures of supplemental
informatio
Corticotroph Aggressive Pituitary Tumors and Carcinomas Frequently Harbor ATRX Mutations
Context: Aggressive pituitary tumors (APTs) are characterized by unusually rapid growth and lack of response to standard treatment. About 1% to 2% develop metastases being classified as pituitary carcinomas (PCs). For unknown reasons, the corticotroph tumors are overrepresented among APTs and PCs. Mutations in the alpha thalassemia/mental retardation syndrome X-linked (ATRX) gene, regulating chromatin remodeling and telomere maintenance, have been implicated in the development of several cancer types, including neuroendocrine tumors. Objective: To study ATRX protein expression and mutational status of the ATRX gene in APTs and PCs. Design: We investigated ATRX protein expression by using immunohistochemistry in 30 APTs and 18 PCs, mostly of Pit-1 and T-Pit cell lineage. In tumors lacking ATRX immunolabeling, mutational status of the ATRX gene was explored. Results: Nine of the 48 tumors (19%) demonstrated lack of ATRX immunolabelling with a higher proportion in patients with PCs (5/18; 28%) than in those with APTs (4/30;13%). Lack of ATRX was most common in the corticotroph tumors, 7/22 (32%), versus tumors of the Pit-1 lineage, 2/24 (8%). Loss-of-function ATRX mutations were found in all 9 ATRX immunonegative cases: nonsense mutations (n = 4), frameshift deletions (n = 4), and large deletions affecting 22-28 of the 36 exons (n = 3). More than 1 ATRX gene defect was identified in 2 PCs. Conclusion: ATRX mutations occur in a subset of APTs and are more common in corticotroph tumors. The findings provide a rationale for performing ATRX immunohistochemistry to identify patients at risk of developing aggressive and potentially metastatic pituitary tumors.Peer reviewe
The Future of the Correlated Electron Problem
The understanding of material systems with strong electron-electron
interactions is the central problem in modern condensed matter physics. Despite
this, the essential physics of many of these materials is still not understood
and we have no overall perspective on their properties. Moreover, we have very
little ability to make predictions in this class of systems. In this manuscript
we share our personal views of what the major open problems are in correlated
electron systems and we discuss some possible routes to make progress in this
rich and fascinating field. This manuscript is the result of the vigorous
discussions and deliberations that took place at Johns Hopkins University
during a three-day workshop January 27, 28, and 29, 2020 that brought together
six senior scientists and 46 more junior scientists. Our hope, is that the
topics we have presented will provide inspiration for others working in this
field and motivation for the idea that significant progress can be made on very
hard problems if we focus our collective energies.Comment: 55 pages, 19 figure
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