Superconductivity and magnetism are adversarial states of matter. The presence of spontaneous magnetic fields inside the superconducting state is, therefore, an intriguing phenomenon prompting ...extensive experimental and theoretical research. In this review, we discuss recent experimental discoveries of unconventional superconductors which spontaneously break time-reversal symmetry and theoretical efforts in understanding their properties. We discuss the main experimental probes and give an extensive account of theoretical approaches to understand the order parameter symmetries and the corresponding pairing mechanisms, including the importance of multiple bands.
The physical and chemical characterisation of meteorites is of paramount importance in the study of the formation of the Solar System. In this work we show the feasibility of a complete set of ...non-destructive measurements to perform such a characterisation using a stony meteorite as a mock-up sample. The identification of the sample as a meteorite was performed by means of gamma ray spectrometry, which identified the presence of cosmogenic
26
Al. Time-of-Flight Neutron Diffraction (ToF-ND) enabled the mineralogical phase quantification and the analysis of the presence of strains and substitutions in each mineral. Neutron Resonance Capture Analysis (NRCA), Neutron Resonance Transmission Imaging (NRTI) and Muonic Atom X-Ray Spectroscopy (MAXRS) allowed a study of the presence and the space distribution of certain elements. Furthermore, micro-Raman Spectroscopy (μRS) and Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDS) were also considered in order to validate the protocol.
The physical and chemical characterisation of meteorites is of paramount importance in the study of the formation of the Solar System.
We present a candidate material, NaYbO2, that realizes the genuine spin-liquid state on the triangular lattice and benchmarks recent theoretical predictions on the relevant spin models. Synchrotron ...x-ray diffraction and neutron scattering exclude both structural disorder and crystal-electric-field randomness. Our thermodynamic measurements, neutron diffraction, and muon spectroscopy coincidentally prove the absence of magnetic order and persistent spin dynamics down to at least 70 mK. Continuous magnetic excitations first observed by inelastic neutron scattering show a gapless feature and the low-energy spectral weight accumulating at the K point of the Brillouin zone, in agreement with theoretical predictions for the spin-liquid phase of triangular antiferromagnets. Such a gapless spin-liquid phase is further confirmed by our magnetic specific heat analysis that reveals a departure from simple power-law behavior. Our work demonstrates that NaYbO2 practically gives direct experimental access to the spin-liquid physics of triangular antiferromagnets.
Scientists, curators, historians and archaeologists are always looking for new techniques for the study of archaeological artefacts, especially if they are non-destructive. With most non-destructive ...investigations, it is challenging to measure beneath the surface. Among the vast board of techniques used for cultural heritage studies, it is difficult to find one able to give information about the bulk and the compositional variations, along with the depth. In addition, most other techniques have self-absorption issues (i.e., only surface sensitive) and limited sensitivity to low Z atoms. In recent years, more and more interest has been growing around large-scale facility-based techniques, thanks to the possibility of adding new and different insights to the study of material in a non-destructive way. Among them, muonic X-ray spectroscopy is a very powerful technique for material characterization. By using negative muons, scientists are able to perform elemental characterization and depth profile studies. In this work, we give an overview of the technique and review the latest applications in the field of cultural heritage.
Abstract
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 order. In the ...low-temperature phase, 12 out of 13 Ta
4+
5
d
-electrons form molecular orbitals in hexagonal star-of-David patterns, leaving one 5
d-
electron with
S
= ½ 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 µ
B
for the size of the magnetic moment, consistent with the orphan-spin scenario.
Filled skutterudite compounds have gained attention recently as an innovative platforms for studying intriguing low-temperature superconducting properties. Regarding the symmetry of the ...superconducting gap, contradicting findings from several experiments have been made for LaRu4As12 and its isoelectronic counterpart, LaOs4As12. In this vein, we report comprehensive bulk and microscopic results on LaOs4As12 utilizing specific heat analysis and muon-spin rotation/relaxation (μSR) measurements. Bulk superconductivity with TC = 3.2 K was confirmed by heat capacity. The superconducting ground state of the filled-skutterudite LaOs4As12 compound is found to have two key characteristics: superfluid density exhibits saturation type behavior at low temperature, which points to a fully gapped superconductivity with gap value of 2Δ/kBTC = 3.26; additionally, the superconducting state does not show any sign of spontaneous magnetic field, supporting the preservation of time-reversal symmetry. These results open the door for the development of La-based skutterudites as special probes for examining the interplay of single- and multiband superconductivity in classical electron–phonon systems.
Muonic Atom X-ray Emission spectroscopy (µ-XES) is a novel elemental technique that exploits the high-energy X-rays emitted from the muonic atom cascade process to characterize materials. At the ISIS ...Neutron and Muon Source, the technique is performed at Port4 of the RIKEN-RAL facility, with a user demand that is increasing every year. To cope with this demand, it is necessary to continue to improve the method, either for the hardware (detectors, acquisition, etc.) or software (data analysis and interpretation). In both cases, Monte Carlo codes play an important role: with a simulation, it is possible to reproduce the experimental setup and provide a reliable quantitative analysis. In this work, we investigate the capabilities of GEANT4 for such applications. From the results, we observed that the generation of X-rays, especially the kα and kβ transition for high Z atoms, are not in agreement with the experimental ones. A solution to this issue, other than an attempt with a small modification of the GEANT4 cascade class, could be provided by a database of transition energy calculated by a Dirac equation software called MuDirac. The software, developed by the UKRI scientific computing department and the ISIS muon group, can compute all the transition energy for a given nuclide. Here, preliminary results of the implementation of the MuDirac database in GEANT4 are reported.
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