arXiv subjects

A. D. Finke

Publications and source records attributed to A. D. Finke.

2 recordsLinked to original sources

arXiv2026

Measurements of enriched 155 Gd and 157Gd converters with the NMX detector on the nTOF EAR2 beam line at CERN

The detectors for the NMX instrument at the European Spallation Source (ESS) in Lund use natural Gd as the neutron converter. In 2024, beam time was obtained at the neutron time-of flight experiment (nTOF) at CERN to study the feasibility of an upgrade to enriched Gd. A 10 x 10 cm^2 prototype of the NMX detector was equipped with two enriched Gd samples (157Gd and 155Gd) that were attached with copper tape to the natural Gd cathode of the detector. Three sets of measurements were taken, with the beam focused on either the natural Gd, the 157Gd, or the 155Gd samples. Using the time-of-flight technique with the subsequent conversion of time-of-flight into energy, the resonant region between 1 eV and 200 eV of the 157Gd and 155Gd cross sections was studied. The peaks in the resonant region were clearly visible, having higher ADC values in the ADC spectrum. Additionally, the resonant peaks had a larger number of counts per energy bin. In the thermal neutron energy range, the count rate at the center of the beam was measured for natural Gd, 157Gd, and 155Gd. Enriched 157Gd showed an efficiency that was between 60 - 180% higher, compared to natural Gd, for neutron wavelengths between 0.8 A and 1.8 A. The measured 60 % increase in efficiency at 1.8 A is lower than expected from simulations (100 %) and previous measurements with solid state detectors (80 %). Gamma background detection, bad focusing, and saturation effects most likely explain this deviation. An upgrade of the natural Gd converter to enriched 157Gd would thus lead to an efficiency increase of at least 60 %. The measurements presented in this paper are the first successful time-of-flight measurements with the NMX detector prototype and the ESS VMM readout.

physics.ins-det↗

arXiv2017

Bulk Fermi-surface of the Weyl type-II semi-metallic candidate MoTe2

The electronic structure of WTe$_2$ and orthorhombic $γ-$MoTe$_2$, are claimed to contain pairs of Weyl type-II points. A series of ARPES experiments claim a broad agreement with these predictions. We synthesized single-crystals of MoTe$_2$ through a Te flux method to validate these predictions through measurements of its bulk Fermi surface (FS) \emph{via} quantum oscillatory phenomena. We find that the superconducting transition temperature of $γ-$MoTe$_2$ depends on disorder as quantified by the ratio between the room- and low-temperature resistivities, suggesting the possibility of an unconventional superconducting pairing symmetry. Similarly to WTe$_2$, the magnetoresistivity of $γ-$MoTe$_2$ does not saturate at high magnetic fields and can easily surpass $10^{6}$ \%. Remarkably, the analysis of the de Haas-van Alphen (dHvA) signal superimposed onto the magnetic torque, indicates that the geometry of its FS is markedly distinct from the calculated one. The dHvA signal also reveals that the FS is affected by the Zeeman-effect precluding the extraction of the Berry-phase. A direct comparison between the previous ARPES studies and density-functional-theory (DFT) calculations reveals a disagreement in the position of the valence bands relative to the Fermi level $\varepsilon_F$. Here, we show that a shift of the DFT valence bands relative to $\varepsilon_F$, in order to match the ARPES observations, and of the DFT electron bands to explain some of the observed dHvA frequencies, leads to a good agreement between the calculations and the angular dependence of the FS cross-sectional areas observed experimentally. However, this relative displacement between electron- and hole-bands eliminates their crossings and, therefore, the Weyl type-II points predicted for $γ-$MoTe$_2$.

cond-mat.mes-hall↗