Real-space investigation of short-range magnetic correlations in fluoride pyrochlores NaCaCo2_2F7_7 and NaSrCo2_2F7_7 with magnetic pair distribution function analysis

We present time-of-flight neutron total scattering and polarized neutron scattering measurements of the magnetically frustrated compounds NaCaCo$_2$F$_7$ and NaSrCo$_2$F$_7$, which belong to a class of recently discovered pyrochlore compounds based on transition metals and fluorine. The magnetic pair distribution function (mPDF) technique is used to analyze and model the total scattering data in real space. We find that a previously-proposed model of short-range XY-like correlations with a length scale of 10-15 \AA, combined with nearest-neighbor collinear antiferromagnetic correlations, accurately describes the mPDF data at low temperature, confirming the magnetic ground state in these materials. This model is further verified by the polarized neutron scattering data. From an analysis of the temperature dependence of the mPDF and polarized neutron scattering data, we find that short-range correlations persist on the nearest-neighbor length scale up to 200 K, approximately two orders of magnitude higher than the spin freezing temperatures of these compounds. These results highlight the opportunity presented by these new pyrochlore compounds to study the effects of geometric frustration at relatively high temperatures, while also advancing the mPDF technique and providing a novel opportunity to investigate a genuinely short-range-ordered magnetic ground state directly in real space

The low-temperature highly correlated quantum phase in the charge-density-wave 1T-TaS_2 compound

A prototypical quasi-2D metallic compound, 1T-TaS_2 has been extensively studied due to an intricate interplay between a Mott-insulating ground state and a charge density-wave (CDW) order. In the low-temperature phase, 12 out of 13 Ta_{4+} 5\textit{d}-electrons form molecular orbitals in hexagonal star-of-David patterns, leaving one 5\textit{d}-electron with \textit{S} = 1/2 spin free. This orphan quantum spin with a large spin-orbit interaction is expected to form a highly correlated phase of its own. And it is most likely that they will form some kind of a short-range order out of a strongly spin-orbit coupled Hilbert space. In order to investigate the low-temperature magnetic properties, we performed a series of measurements including neutron scattering and muon experiments. The obtained data clearly indicate the presence of the short-ranged phase and put the upper bound on ~ 0.4 \textit{\mu}_B for the size of the magnetic moment, consistent with the orphan-spin scenario.Comment: 11 pages, 4 figures + supplemental material. Accepted by npj Quantum Material

The thermal denaturation of DNA studied with neutron scattering

The melting transition of deoxyribonucleic acid (DNA), whereby the strands of the double helix structure completely separate at a certain temperature, has been characterized using neutron scattering. A Bragg peak from B-form fibre DNA has been measured as a function of temperature, and its widths and integrated intensities have been interpreted using the Peyrard-Bishop-Dauxois (PBD) model with only one free parameter. The experiment is unique, as it gives spatial correlation along the molecule through the melting transition where other techniques cannot.Comment: accepted for publication in Physical Review Letter

The elevated Curie temperature and half-metallicity in the ferromagnetic semiconductor Lax_{x}Eu1−x_{1-x}O

Here we study the effect of La doping in EuO thin films using SQUID magnetometry, muon spin rotation ($\mu$SR), polarized neutron reflectivity (PNR), and density functional theory (DFT). The $\mu$SR data shows that the La$_{0.15}$Eu$_{0.85}$O is homogeneously magnetically ordered up to its elevated $T_{\rm C}$. It is concluded that bound magnetic polaron behavior does not explain the increase in $T_{\rm C}$ and an RKKY-like interaction is consistent with the $\mu$SR data. The estimation of the magnetic moment by DFT simulations concurs with the results obtained by PNR, showing a reduction of the magnetic moment per La$_{x}$Eu$_{1-x}$O for increasing lanthanum doping. This reduction of the magnetic moment is explained by the reduction of the number of Eu-4$f$ electrons present in all the magnetic interactions in EuO films. Finally, we show that an upwards shift of the Fermi energy with La or Gd doping gives rise to half-metallicity for doping levels as high as 3.2 %.Comment: 7 pages, 11 figure

Isostructural Mott transition in 2D honeycomb antiferromagnet V 0.9 PS 3

Abstract: The MPX3 family of magnetic van-der-Waals materials (M denotes a first row transition metal and X either S or Se) are currently the subject of broad and intense attention for low-dimensional magnetism and transport and also for novel device and technological applications, but the vanadium compounds have until this point not been studied beyond their basic properties. We present the observation of an isostructural Mott insulator–metal transition in van-der-Waals honeycomb antiferromagnet V0.9PS3 through high-pressure x-ray diffraction and transport measurements. We observe insulating variable-range-hopping type resistivity in V0.9PS3, with a gradual increase in effective dimensionality with increasing pressure, followed by a transition to a metallic resistivity temperature dependence between 112 and 124 kbar. The metallic state additionally shows a low-temperature upturn we tentatively attribute to the Kondo effect. A gradual structural distortion is seen between 26 and 80 kbar, but no structural change at higher pressures corresponding to the insulator–metal transition. We conclude that the insulator–metal transition occurs in the absence of any distortions to the lattice—an isostructural Mott transition in a new class of two-dimensional material, and in strong contrast to the behavior of the other MPX3 compounds

Revisiting spin ice physics in the ferromagnetic Ising pyrochlore Pr2_2Sn2_2O7_7

Pyrochlore materials are characterized by their hallmark network of corner-sharing rare-earth tetrahedra, which can produce a wide array of complex magnetic ground states. Ferromagnetic Ising pyrochlores often obey the "two-in-two-out" spin ice rules, which can lead to a highly-degenerate spin structure. Large moment systems, such as Ho$_2$Ti$_2$O$_7$ and Dy$_2$Ti$_2$O$_7$, tend to host a classical spin ice state with low-temperature spin freezing and emergent magnetic monopoles. Systems with smaller effective moments, such as Pr$^{3+}$-based pyrochlores, have been proposed as excellent candidates for hosting a "quantum spin ice" characterized by entanglement and a slew of exotic quasiparticle excitations. However, experimental evidence for a quantum spin ice state has remained elusive. Here, we show that the low-temperature magnetic properties of Pr$_2$Sn$_2$O$_7$ satisfy several important criteria for continued consideration as a quantum spin ice. We find that Pr$_2$Sn$_2$O$_7$ exhibits a partially spin-frozen ground state with a large volume fraction of dynamic magnetism. Our comprehensive bulk characterization and neutron scattering measurements enable us to map out the magnetic field-temperature phase diagram, producing results consistent with expectations for a ferromagnetic Ising pyrochlore. We identify key hallmarks of spin ice physics, and show that the application of small magnetic fields ($\mu_0 H_c \sim$0.75T) suppresses the spin ice state and induces a long-range ordered magnetic structure. Together, our work clarifies the current state of Pr$_2$Sn$_2$O$_7$ and encourages future studies aimed at exploring the potential for a quantum spin ice ground state in this system

Tumour-selective activity of RAS-GTP inhibition in pancreatic cancer

Broad-spectrum RAS inhibition has the potential to benefit roughly a quarter of human patients with cancer whose tumours are driven by RAS mutations1,2. RMC-7977 is a highly selective inhibitor of the active GTP-bound forms of KRAS, HRAS and NRAS, with affinity for both mutant and wild-type variants3. More than 90% of cases of human pancreatic ductal adenocarcinoma (PDAC) are driven by activating mutations in KRAS4. Here we assessed the therapeutic potential of RMC-7977 in a comprehensive range of PDAC models. We observed broad and pronounced anti-tumour activity across models following direct RAS inhibition at exposures that were well-tolerated in vivo. Pharmacological analyses revealed divergent responses to RMC-7977 in tumour versus normal tissues. Treated tumours exhibited waves of apoptosis along with sustained proliferative arrest, whereas normal tissues underwent only transient decreases in proliferation, with no evidence of apoptosis. In the autochthonous KPC mouse model, RMC-7977 treatment resulted in a profound extension of survival followed by on-treatment relapse. Analysis of relapsed tumours identified Myc copy number gain as a prevalent candidate resistance mechanism, which could be overcome by combinatorial TEAD inhibition in vitro. Together, these data establish a strong preclinical rationale for the use of broad-spectrum RAS-GTP inhibition in the setting of PDAC and identify a promising candidate combination therapeutic regimen to overcome monotherapy resistance

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700