An optical NMR spectrometer for Larmor-beat detection and high-resolution POWER NMR

Optical nuclear magnetic resonance (ONMR) is a powerful probe of electronic properties in III-V semiconductors. Larmor-beat detection (LBD) is a sensitivity optimized, time-domain NMR version of optical detection based on the Hanle effect. Combining LBD ONMR with the line-narrowing method of POWER (perturbations observed with enhanced resolution) NMR further enables atomically detailed views of local electronic features in III-Vs. POWER NMR spectra display the distribution of resonance shifts or line splittings introduced by a perturbation, such as optical excitation or application of an electric field, that is synchronized with a NMR multiple-pulse time-suspension sequence. Meanwhile, ONMR provides the requisite sensitivity and spatial selectivity to isolate local signals within macroscopic samples. Optical NMR, LBD, and the POWER method each introduce unique demands on instrumentation. Here, we detail the design and implementation of our system, including cryogenic, optical, and radio-frequency components. The result is a flexible, low-cost system with important applications in semiconductor electronics and spin physics. We also demonstrate the performance of our systems with high-resolution ONMR spectra of an epitaxial AlGaAs/GaAs heterojunction. NMR linewidths down to 4.1 Hz full width at half maximum were obtained, a 10^3-fold resolution enhancement relative any previous optically detected NMR experiment

DAMARIS – a flexible and open software platform for NMR spectrometer control: DAMARIS – a flexible and open software platform for NMRspectrometer control

Home-built NMR spectrometers with self-written control software have a long tradition in porous media research. Advantages of such spectrometers are not just lower costs but also more flexibility in developing new experiments (while commercial NMR systems are typically optimized for standard applications such as spectroscopy, imaging or quality control applications). Increasing complexity of computer operating systems, higher expectations with respect to user-friendliness and graphical user interfaces as well as increasing complexity of the NMR experiments themselves have made spectrometer control software development a more complex task than it used to be some years ago. Like that, it becomes more and more complicated for an individual lab to maintain and develop an infrastructure of purely homebuilt NMR systems and software. Possible ways out are: ● commercial NMR hardware with full-blown proprietary software or ● semistandardized home-built equipment and common open-source software environment for spectrometer control. Our present activities in Darmstadt aim at providing a nucleus for the second option: DArmstadt MAgnetic Resonance Instrument Software (DAMARIS) [1]. Based on an ordinary PC, pulse control cards and ADC cards, we have developed an NMR spectrometer control platform that comes at a price tag of about 8000 Euro. The present functionalities of DAMARIS are mainly focused on TD-NMR: the software was successfully used in single-sided NMR [2], pulsed and static field gradient NMR diffusometry [3]. Further work with respect to multipulse/multitriggering experiments in the time domain [4] and solid state NMR spectroscopy multipulse experiments are under development

Open-source magnetic resonance imaging : Improving access, science, and education through global collaboration

The authors would like to thank all the authors that are sharing their work open-source and all the supporters of the Open Source Imaging Initiative (OSI2). The project (21NRM05 and 22HLT02 A4IM) has received funding from the European Partnership on Metrology, co-financed by the European Union's Horizon Europe Research and Innovation Programme and by the Participating States. This research is funded by dtec.bw- Digitalization and Technology Research Center of the Bundeswehr. dtec.bw is funded by the European Union - NextGeneration EU. Part of the image reconstruction used here was developed by the CCP PETMR and CCP SynerBi (https://www.ccppetmr.ac.uk/), UK EPSRC grants EP/P022200/1, EP/M022587/1 and EP/T026693/1. This work made use of computational support by CoSeC, the Computational Science Centre for Research Communities via CCP-SyneRBI and CCPi. RG Nunes acknowledges funding from Fundação para a Ciência e a Tecnologia (grants UIDP/50009/2020 and LA/P/0083/2020). Ruben Pellicer-Guridi has been funded by the European Union's Marie Skłodowska-Curie project nr. 101030868. Open Access funding enabled and organized by Projekt DEAL.Peer reviewe

In situ SABRE hyperpolarisation with Earth’s field NMR detection

Hyperpolarisation methods, which increase the sensitivity of NMR and MRI, have the potential to expand the range of applications of these powerful analytical techniques and to enable the use of smaller and cheaper devices. The signal amplification by reversible exchange (SABRE) method is of particular interest because it is relatively low-cost, straight-forward to implement, produces high-levels of renewable signal enhancement, and can be interfaced with low-cost and portable NMR detectors. In this work we demonstrate an in situ approach to SABRE hyperpolarisation that can be achieved using a simple, commercially-available Earth’s field NMR detector to provide 1H polarisation levels of up to 3.36 %. This corresponds to a signal enhancement over the Earth’s magnetic field by a factor of ε > 2e8. The key benefit of our approach is that it can be used to probe the polarisation transfer process at the heart of the SABRE technique directly. In particular, we demonstrate the use of in situ hyperpolarisation to observe the activation of the SABRE catalyst, the build-up of signal in the polarisation transfer field (PTF), the dependence of the hyperpolarisation level on the strength of the PTF, and the rate of decay of the hyperpolarisation in the ultra-low-field regime

Nuclear magnetic resonance studies of magnetic fluctuations and nematic order in iron-based superconductors

This thesis illustrates the use of the nuclear magnetic resonance (NMR) technique as a local probe for the study of static and dynamic magnetism in the iron-based superconductors. First, a Korringa ratio analysis of 59Co and 75As NMR data reveals the existence of ferromagnetic (FM) spin fluctuations in SrCo2As2 and the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. The analysis further shows that the FM fluctuations compete with AFM fluctuations to suppress superconductivity in these materials. The FM fluctuations are thus a crucial ingredient to understanding the variability of the superconducting transition temperature (Tc) and the shape of the superconducting dome in these and other iron-pnictide families. Secondly, a study of KFe2As2 under pressures up to 2.1 GPa reveals a crossover between a high-temperature incoherent, local-moment behavior and a low-temperature coherent behavior at a crossover temperature, T*. The T* is found to increase monotonically with pressure, consistent with increasing hybridization between localized 3d orbital-derived bands with the itinerant electron bands. No anomaly in T* is seen at the critical pressure where a change of slope of Tc(p) has been observed. In the superconducting state, two-component nuclear spin-lattice relaxation is observed at low temperatures, suggesting the existence of two distinct local electronic environments. Finally, 77Se-NMR studies of FeSe subjected to external pressure and sulfur doping are presented. In pure FeSe under pressure, the NMR spectra reveal the existence of a short-range, local nematic ordered state above the bulk nematic ordering temperature. Furthermore, this local nematic order does not compete with low-energy AFM spin fluctuations. In sulfur-doped FeSe(1−x)Sx, the observed behavior of the magnetic fluctuations parallels the Tc, providing strong evidence for the primary importance of magnetic fluctuations for superconductivity, despite the presence of nematic quantum criticality in this system