37 research outputs found
The pairing symmetry in quasi-one-dimensional superconductor Rb2Mo3As3
Quasi-one-dimensional electron systems display intrinsic instability towards
long-range ordered phases at sufficiently low temperatures. The superconducting
orders are of particular interest as they can possess either singlet or triplet
pairing symmetry and frequently compete with magnetism. Here we report on muon
spin rotation and relaxation (SR) study of RbMoAs
characterised by one of the highest critical temperatures $T_{\rm c}=10.4\
\mathrm{K}\mathrm{\mu}T_{\rm c}s-p-d-s-\Delta_0T_{\rm c}2\Delta_0/k_{\rm B}T_{\rm c}=2.74(1)p-d-2\Delta_0/k_{\rm B}T_{\rm c}=3.50(2)2\Delta_0/k_{\rm B}T_{\rm c}=4.08(1)_2_3_3$.Comment: 6 page
Influence of La and Mn vacancies on the electronic and magnetic properties of LaMnOâ thin films grown by pulsed laser deposition
With pulsed laser deposition, we have grown c axis oriented thin films of the nominal composition LaMnO3 (LMO) on LSAT(001) substrates. We find that, depending on the oxygen background pressure during growth, the LMO films contain sizeable amounts of La and/or Mn vacancies that strongly influence their electronic and magnetic properties. Specifically, we show that the Mn/La ratio can be systematically varied from 0.92 at 0.11 mbar to 1.09 at 0.30 mbar of oxygen. The cationic vacancies have markedly different effects that become most pronounced once the samples are fully oxygenated and thus strongly hole doped. All as-grown and thus slightly oxygen-deficient LMO films are ferromagnetic insulators with saturation moments in excess of 2.5 ÎŒB per Mn ion, their transport and optical properties can be understood in terms of trapped ferromagnetic polarons. Upon oxygen annealing, the most La-deficient films develop a metallic response with an even larger ferromagnetic saturation moment of 3.8 ÎŒB per Mn ion. In contrast, in the oxygenated Mn-deficient films, the ferromagnetic order is strongly suppressed to less than 0.5 ÎŒB per Mn ion, and the transport remains insulatorlike. We compare our results with the ones that were previously obtained on bulk samples and present an interpretation in terms of the much stronger disruption of the electronic and magnetic structure by the Mn vacancies as compared to the La vacancies. We also discuss the implications for the growth of LMO thin films with well-defined physical properties that are a prerequisite for the study of interface effects in multilayers
Magnetic nature of wolframite MgReO
Rhenium oxides belonging to the family ReO where is a metal
cation, exhibit interesting electronic and magnetic properties. In this study
we have utilized the muon spin rotation/relaxation (SR) technique to
study the magnetic properties of the MgReO compound. To the best of our
knowledge, this is the first investigation reported on this interesting
material, that is stabilized in a wolframite crystal structure using a special
high-pressure synthesis technique. Bulk magnetic studies show the onset of an
antiferromagnetic (AF) long range order, or a possible singlet spin state at
~K, with a subtle second high-temperature transition at
~K. Both transitions are also confirmed by heat capacity
() measurements. From our SR measurements, it is clear that the
sample enters an AF order below ~K. We find no
evidence of magnetic signal above , which indicates that is likely linked to a structural transition. Further, via sensitive zero
field (ZF) SR measurements we find evidence of a spin reorientation at
~K. This points towards a transition from a collinear AF
into a canted AF order at low temperature, which is proposed to be driven by
competing magnetic interactions
First demonstration of tuning between the Kitaev and Ising limits in a honeycomb lattice
Recent observations of novel spin-orbit coupled states have generated
tremendous interest in transition metal systems. A prime example is the
state in iridate materials and -RuCl
that drives Kitaev interactions. Here, by tuning the competition between
spin-orbit interaction () and trigonal crystal field
splitting (), we restructure the spin-orbital wave functions
into a novel state that drives Ising interactions. This is
done via a topochemical reaction that converts LiRhO to
AgLiRhO, leading to an enhanced trigonal distortion and a
diminished spin-orbit coupling in the latter compound. Using perturbation
theory, we present an explicit expression for the new state
in the limit realized in
AgLiRhO, different from the conventional
state in the limit realized in LiRhO. The change of ground state is
followed by a dramatic change of magnetism from a 6 K spin-glass in
LiRhO to a 94 K antiferromagnet in AgLiRhO. These
results open a pathway for tuning materials between the two limits and creating
a rich magnetic phase diagram.Comment: 22 pages, 4 figure
Probing the magnetic polaron state in the ferromagnetic semiconductor HgCr2Se4 with muon-spin spectroscopy and resistance-fluctuation measurements
Combined resistance noise and muon-spin relaxation (ÎŒSR) measurements of the ferromagnetic semiconductor HgCr2Se4 suggest a degree of magnetoelectric coupling and provide evidence for the existence of isolated magnetic polarons. These form at elevated temperatures and undergo a percolation transition with a drastic enhancement of the low-frequency 1/ f -type charge fluctuations at the insulator-to-metal transition at âŒ95â98 K in the vicinity of the magnetic ordering temperature TC ⌠105â107 K. Upon approaching the percolation threshold from above, the strikingly unusual dynamics of a distinct two-level fluctuator superimposed on the 1/ f noise can be described by a slowing down of the dynamics of a nanoscale magnetic cluster, a magnetic polaron, when taking into account an effective radius of the polaron depending on the spin correlation length. Coinciding temperature scales found in ÎŒSR and noise measurements suggest changes in the magnetic dynamics over a wide range of frequencies and are consistent with the existence of large polarized and domain-wall-like regions at low temperatures, that result from the freezing of spin dynamics at the magnetic polaron percolation transition
Partitioning the two-leg spin ladder in Ba2Cu1â xZnxTeO6 : from magnetic order through spin-freezing to paramagnetism
E.J.C., O.M., and C.P. acknowledge financial support from the Leverhulme Trust Research Project Grant No. RPG-2017-109. O.M. is grateful for funding via the Leverhulme Trust Early Career Fellowship ECF-2021-170. A.S.G. acknowledges funding through an EPSRC Early Career Fellowship EP/ T011130/1. A.S.G. and H.T. acknowledge funding through the Humboldt Foundation and the Max Planck Institute for Solid State Research. The authors thank the Science and Technology Facilities Council for beamtime allocated at ISIS through proposal RB1990046 (DOI: 10. 5286/ISIS.E.RB1990046) and the Swiss Muon Source at the Paul Scherrer Institute through proposal numbers 20150959 and 20211440. The authors are grateful for access to the MPMS3 instrument at The Royce Discovery Centre at the University of Sheffield (EPSRC grant no. EP/R00661X/1) and the PPMS instrument at the University of St. Andrews (EPSRC grant no. EP/T031441/1).Ba2CuTeO6 has attracted significant attention as it contains a two-leg spin ladder of Cu2+ cations that lies in close proximity to a quantum critical point. Recently, Ba2CuTeO6 has been shown to accommodate chemical substitutions, which can significantly tune its magnetic behavior. Here, we investigate the effects of substitution for non-magnetic Zn2+ impurities at the Cu2+ site, partitioning the spin ladders. Results from bulk thermodynamic and local muon magnetic characterization on the Ba2Cu1 â xZnxTeO6 solid solution (0 †x †0.6) indicate that Zn2+ partitions the Cu2+ spin ladders into clusters and can be considered using the percolation theory. As the average cluster size decreases with increasing Zn2+ substitution, there is an evolving transition from long-range order to spin-freezing as the critical cluster size is reached between x = 0.1 to x = 0.2, beyond which the behavior became paramagnetic. This demonstrates well-controlled tuning of the magnetic disorder, which is highly topical across a range of low-dimensional Cu2+-based materials. However, in many of these cases, the chemical disorder is also relatively strong in contrast to Ba2CuTeO6 and its derivatives. Therefore, Ba2Cu1 â xZnxTeO6 provides an ideal model system for isolating the effect of defects and segmentation in low-dimensional quantum magnets.Publisher PDFPeer reviewe
Entanglement between Muon and I > 1/2 Nuclear Spins as a Probe of Charge Environment
We report on the first example of quantum coherence between the spins of muons and quadrupolar nuclei. We reveal that these entangled states are highly sensitive to a local charge environment and thus, can be deployed as a functional quantum sensor of that environment. The quantum coherence effect was observed in vanadium intermetallic compounds which adopt the A15 crystal structure, and whose members include all technologically pertinent superconductors. Furthermore, the extreme sensitivity of the entangled states to the local structural and electronic environments emerges through the quadrupolar interaction with the electric field gradient due to the charge distribution at the nuclear (I >1/2) sites. This case study demonstrates that positive muons can be used as a quantum sensing tool to also probe structural and charge-related phenomena in materials, even in the absence of magnetic degrees of freedom
Single-domain stripe order in a high-temperature superconductor
The coupling of spin, charge and lattice degrees of freedom results in the emergence of novel states of matter across many classes of strongly correlated electron materials. A model example is unconventional superconductivity, which is widely believed to arise from the coupling of electrons via spin excitations. In cuprate high-temperature superconductors, the interplay of charge and spin degrees of freedom is also reflected in a zoo of charge and spin-density wave orders that are intertwined with superconductivity. A key question is whether the different types of density waves merely coexist or are indeed directly coupled. Here we profit from a neutron scattering technique with superior beam-focusing that allows us to probe the subtle spin-density wave order in the prototypical high-temperature superconductor LaSrCuO under applied uniaxial pressure to demonstrate that the two density waves respond to the external tuning parameter in the same manner. Our result shows that suitable models for high-temperature superconductivity must equally account for charge and spin degrees of freedom via uniaxial charge-spin stripe fluctuations
PHT427 as an effective New Delhi metallo-ÎČ-lactamase-1 (NDM-1) inhibitor restored the susceptibility of meropenem against Enterobacteriaceae producing NDM-1
IntroductionWith the increasingly serious problem of bacterial drug resistance caused by NDM-1, it is an important strategy to find effective inhibitors to assist ÎČ-lactam antibiotic treatment against NDM-1 resistant bacteria. In this study, PHT427 (4-dodecyl-N-1,3,4-thiadiazol-2-yl-benzenesulfonamide) was identified as a novel NDM-1 inhibitor and restored the susceptibility of meropenem against Enterobacteriaceae producing NDM-1.MethodsWe used a high throughput screening model to find NDM-1 inhibitor in the library of small molecular compounds. The interaction between the hit compound PHT427 and NDM-1 was analyzed by fluorescence quenching, surface plasmon resonance (SPR) assay, and molecular docking analysis. The efficacy of the compound in combination with meropenem was evaluated by determining the FICIs of Escherichia coli BL21(DE3)/pET30a(+)-blaNDMâ1 and Klebsiella pneumoniae clinical strain C1928 (producing NDM-1). In addition, the mechanism of the inhibitory effect of PHT427 on NDM-1 was studied by site mutation, SPR, and zinc supplementation assays.ResultsPHT427 was identified as an inhibitor of NDM-1. It could significantly inhibit the activity of NDM-1 with an IC50 of 1.42 ÎŒmol/L, and restored the susceptibility of meropenem against E. coli BL21(DE3)/pET30a(+)-blaNDMâ1 and K. pneumoniae clinical strain C1928 (producing NDM-1) in vitro. The mechanism study indicated that PHT427 could act on the zinc ions at the active site of NDM-1 and the catalytic key amino acid residues simultaneously. The mutation of Asn220 and Gln123 abolished the affinity of NDM-1 by PHT427 via SPR assay.DiscussionThis is the first report that PHT427 is a promising lead compound against carbapenem-resistant bacteria and it merits chemical optimization for drug development