Echo Experiments Research Articles

X-Band Single Chip Integrated Pulsed Electron Spin Resonance Microsystem.

We report on the design and characterization of a single chip integrated pulsed electron spin resonance detector operating at 9.1 GHz. The microsystem consists of an excitation microcoil, a detection microcoil, a low noise microwave preamplifier, a mixer, and an intermediate frequency (IF) amplifier. The chip area is about 0.7 mm2. To exemplify its possible applications, we report the results of single pulse, Rabi nutation, Hahn echo, two echoes, Carr-Purcell, and inversion recovery echo experiments performed on 0.02 and 0.05 nL samples of α, γ-bisdiphenylene-β-phenylallyl (BDPA) and 1% BDPA in polystyrene (BDPA:PS) at room temperature. The measured spin sensitivity is about 8 × 107 spins/Hz1/2 on a sensitive volume of about 0.1 nL. The microsystem power consumption is less than 100 mW, the radio frequency (RF) input bandwidth is 8.8 to 9.8 GHz, the IF output bandwidth is DC to 350 MHz, and the deadtime is less than 30 ns.

Limitations on the maximal level of entanglement of two singlet–triplet qubits in GaAs quantum dots

We analyze in detail a procedure of entangling of two singlet–triplet (S–T0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{0}$$\\end{document}) qubits operated in a regime when energy associated with the magnetic field gradient, ΔBz\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta B_{z}$$\\end{document}, is an order of magnitude smaller than the exchange energy, J, between singlet and triplet states (Shulman et al. in Science 336:202, 2012). We have studied theoretically a single S–T0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{0}$$\\end{document} qubit in free induction decay and spin echo experiments. We have obtained analytical expressions for the time dependence of components of its Bloch vector for quasistatic fluctuations of ΔBz\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta B_{z}$$\\end{document} and quasistatic or dynamical 1/fβ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1/f^{\\beta }$$\\end{document}-type fluctuations of J. We have then considered the impact of fluctuations of these parameters on the efficiency of the entangling procedure which uses an Ising-type coupling between two S–T0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{0}$$\\end{document} qubits. In particular, we have obtained an analytical expression for evolution of two qubits affected by 1/fβ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1/f^{\\beta }$$\\end{document}-type fluctuations of J. This expression indicates the maximal level of entanglement that can be generated by performing the entangling procedure. Our results deliver also an evidence that in the above-mentioned experiment S–T0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{0}$$\\end{document} qubits were affected by uncorrelated 1/fβ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1/f^{\\beta }$$\\end{document} charge noises.

Enhancement of silicon vacancy fluorescence intensity in silicon carbide using a dielectric cavity.

Over the past decades, spin qubits in silicon carbide (SiC) have emerged as promising platforms for a wide range of quantum technologies. The fluorescence intensity holds significant importance in the performance of quantum photonics, quantum information process, and sensitivity of quantum sensing. In this work, a dual-layer Au/SiO2 dielectric cavity is employed to enhance the fluorescence intensity of a shallow silicon vacancy ensemble in 4H-SiC. Experimental results demonstrate an effective fourfold augmentation in fluorescence counts at saturating laser power, corroborating our theoretical predictions. Based on this, we further investigate the influence of dielectric cavities on the contrast and linewidth of optically detected magnetic resonance (ODMR). There is a 1.6-fold improvement in magnetic field sensitivity. In spin echo experiments, coherence times remain constant regardless of the thickness of dielectric cavities. These experiments pave the way for broader applications of dielectric cavities in SiC-based quantum technologies.

Dynamic structure factor of undulating vesicles: finite-size and spherical geometry effects with application to neutron spin echo experiments.

We consider the dynamic structure factor (DSF) of quasi-spherical vesicles and present a generalization of an expression that was originally formulated by Zilman and Granek (ZG) for scattering from isotropically oriented quasi-flat membrane plaquettes. The expression is obtained in the form of a multi-dimensional integral over the undulating membrane surface. The new expression reduces to the original stretched exponential form in the limit of sufficiently large vesicles, i.e., in the micron range or larger. For much smaller unilamellar vesicles, deviations from the asymptotic, stretched exponential equation are noticeable even if one assumes that the Seifert-Langer leaflet density mode is completely relaxed and membrane viscosity is neglected. To avoid the need for an exhaustive numerical integration while fitting to neutron spin echo (NSE) data, we provide a useful approximation for polydisperse systems that tests well against the numerical integration of the complete expression. To validate the new expression, we performed NSE experiments on variable-size vesicles made of a POPC/POPS lipid mixture and demonstrate an advantage over the original stretched exponential form or other manipulations of the original ZG expression that have been deployed over the years to fit the NSE data. In particular, values of the membrane bending rigidity extracted from the NSE data using the new approximations were insensitive to the vesicle radii and scattering wavenumber and compared very well with expected values of the effective bending modulus ([Formula: see text]) calculated from results in the literature. Moreover, the generalized scattering theory presented here for an undulating quasi-spherical shell can be easily extended to other models for the membrane undulation dynamics beyond the Helfrich Hamiltonian and thereby provides the foundation for the study of the nanoscale dynamics in more complex and biologically relevant model membrane systems.

Probing the “Dead-Time” in NMR by Combining Single Pulse and Solid Echo Experiments Followed by a Global Model Fit Analysis

The main question addressed in this work is how to probe the “effective dead-time” in an NMR instrument, i.e., the time needed to blank the receiver after an rf-pulse excitation to prevent damage to the receiver and to avoid any distortion of the NMR signal being sampled. The strategy is to design a suitable FID-model to fit the single pulse excitation (SPE) and solid echo pulse (SEPS) data (on solid Tricosane) using a Global model-fit analysis technique. The derived dead time is discussed with respect to sampling temperature (25–40 °C) and—in particular—with respect to the number of SEPS data involved in the Global fit analysis by applying the Bayesian Information Criterion (BIC) in combination with more traditional statistical analysis. It is concluded that the “effective dead time” can be determined within a standard error of less than 2.5%.

Conductivity Improvement of LiBF4 Containing Electrolyte for Enhanced Application in Lithium-Ion Batteries

In view of a possible cost reduction and safety improvement of Lithium-Ion-Batteries (LIBs), the exchangeability of the common electrolyte salt lithium hexafluorophosphate LiPF6 with lithium tetrafluoroborate LiBF4 was investigated.[1,2] Replacement of LiPF6 with LiBF4 was considered due to the salt’s superior thermal stability and moisture stability compared to LiPF6. While LiBF4 was repeatedly studied for application in LIBs, low conductivity compared to analogous electrolyte solutions with LiPF6 is referred to as one of the main drawbacks of LiBF4 electrolytes.[1,3] These differences in electrolyte solution conductivity are usually related to an increased tendency for ion pair formation between the [BF4]– anion and Li+.[1,4] To overcome the strong ion-pairing between Li+ and [BF4]–, the conductivity of a LiBF4 electrolyte solution was improved by introduction of different amounts of 1,2-dimethoxyethane (DME) as bidentate ligand into the commercially available electrolyte solvent L57 (ethyl carbonate : ethylmethyl carbonate, 30 : 70, by wt%). The solvent modification was carried out in consideration of the published superior oxidative stability of lithium associated oligoethers compared to non-associated analogues.[5] All electrolyte solutions were investigated for their electrochemical behavior and their performance in Lithium-Ion-Battery (LIB) cells with commercially available cell components. All results were referred to analogous measurements with LiPF6 and LiBF4 electrolyte solution in the unmodified L57 solvent. Electrochemical characterization was performed by conductivity measurements and cyclic voltammetry. Battery cell experiments were carried out for Lithium-Metal cells with excess of electrolyte solution and Lithium-Ion cells. Lithium nickel cobalt manganese oxide (NCM622) electrodes were implemented as positive electrodes and Lithium-Ion cells were assembled with graphite electrodes as negative electrodes. All battery cells were investigated for their ambient temperature cycle life. Furthermore, ambient temperature C-rate stability of Li-Ion cells was examined. In view of the electrochemical behavior, conductivity of LiBF4 electrolytes significantly increases with the introduction of DME to the chosen electrolyte solvent, which is shown in the figure presenting the temperature dependent conductivities of the investigated electrolyte solutions. This conductivity enhancement is decreasing towards the contribution of more than two equivalents of DME per Li+ ion in the electrolyte solution. Cyclic voltammetry experiments of the electrolyte solutions show negligible effects on reductive stability of the electrolyte solution system, while the respective oxidative stability distinctly decreases with the addition of DME into the electrolyte solvent. A decreased oxidative stability is considered to induce parasitic reactions at the positive electrode, which presumably can be affected by change of positive electrode material. Despite the differences in conductivity, battery cell experiments present LiBF4 as a comparable electrolyte salt to LiPF6, with a performance difference that could possibly be overcome by utilization of the right electrolyte additive(s). The investigated oligoether containing electrolyte solutions show inferior battery performance compared to the unmodified carbonate-based electrolyte solvent. Since the battery cycling experiments were prepared at the oxidative stability limit of these electrolyte solutions, these electrolyte solutions might still create promising battery cell performance with a change of positive electrode material. In order to further investigate the ion pair association of lithium cations and tetrafluoroborate anions, the utilized system was additionally investigated spectroscopically and with quantum chemical calculations on the basis of density functional theory. Spectroscopic characterization was carried out with help of stimulated spin echo experiments in nuclear magnetic spectroscopy and Raman spectroscopy measurements. Both spectroscopies present changes in the associated structure of lithium cation and tetrafluoroborate anions by addition of DME to the commercial electrolyte solvent. For further conclusions, these results were compared with the calculations prepared for the electrolyte solution system. In summary, spectroscopic characterization and quantum chemical calculations indicate a modification of the associated structures in solution by the addition of DME to the chosen electrolyte solvent. By comparison of all collected results, research concerning the application of LiBF4 electrolytes should be continued with adaption of electrolyte solution additives or positive electrode material, respectively.[1] C. Daniel, J. O. Besenhard (Hrsg.) Handbook of battery materials, Wiley-VCH-Verl., Weinheim, 2011.[2] M. Winter, R. J. Brodd, Chem. Rev. 2004, 104, 4245.[3] R. Korthauer (Hrsg.) Handbuch Lithium-Ionen-Batterien, Springer Vieweg, Berlin, Heidelberg, 2013.[4] H. Tsunekawa, A. Narumi, M. Sano, A. Hiwara, M. Fujita, H. Yokoyama, J. Phys. Chem. B 2003, 107, 10962.[5] K. Yoshida, M. Nakamura, Y. Kazue, N. Tachikawa, S. Tsuzuki, S. Seki, K. Dokko, M. Watanabe, J. Am. Chem. Soc. 2011, 133, 13121. Figure 1

Development and characterisation of high-resolution microcalorimeter detectors for the ECHo-100k experiment

The goal of the ECHo experiment is a direct determination of the absolute scale of the neutrino mass by the analysis of the end-point region of the 163Ho electron capture (EC) spectrum. The results of the first phase of the experiment, ECHo-1k, have paved the way for the current phase, ECHo-100k, which aims at a sensitivity below 2eV on the effective electron neutrino mass. In order to reach this goal, a new generation of high-resolution magnetic microcalorimeters with embedded 163Ho have been developed and characterised. The design has been optimised to meet all the challenging requirements of the ECHo-100k experimental phase, such as excellent energy resolution, wafer scale implantation and multi-chip operation with multiplexing read-out. We present the optimisation studies, the final design of the detector array and the first characterisation studies. The obtained results demonstrate that the detectors fully match and even surpass the requirements for the current experimental phase, ECHo-100k.

Design of acoustic impedance gradient matching layers

This article proposes a new acoustic impedance gradient matching layer based on phononic crystal theory to further expand the bandwidth of piezoelectric ultrasonic transducers and improve their working efficiency. The matching layer is made of a composite of two different materials and its transverse structure can be regarded as a one-dimensional phononic crystal. This structure can effectively reduce the transverse vibration of the transducer and enhance the longitudinal vibration. In addition, the gradient alteration of acoustic impedance in the longitudinal direction of the matching layer improves its acoustic impedance matching performance with the medium. Through theoretical calculations and finite element simulations, we obtained the equivalent acoustic parameters of the gradient matching layer and investigated the suppression of transverse vibration by its structural properties based on the band gap theory. Finally, a sample of the transducer equipped with the gradient matching layer was prepared and its working performance was measured by pulse echo experiments, which is a significant improvement compared to the conventional λ/4 matching layer transducer.

Coherent control of an ultrabright single spin in hexagonal boron nitride at room temperature

Hexagonal boron nitride (hBN) is a remarkable two-dimensional (2D) material that hosts solid-state spins and has great potential to be used in quantum information applications, including quantum networks. However, in this application, both the optical and spin properties are crucial for single spins but have not yet been discovered simultaneously for hBN spins. Here, we realize an efficient method for arraying and isolating the single defects of hBN and use this method to discover a new spin defect with a high probability of 85%. This single defect exhibits outstanding optical properties and an optically controllable spin, as indicated by the observed significant Rabi oscillation and Hahn echo experiments at room temperature. First principles calculations indicate that complexes of carbon and oxygen dopants may be the origin of the single spin defects. This provides a possibility for further addressing spins that can be optically controlled.

3D magnetic resonance fingerprinting on a low-field 50 mT point-of-care system prototype: evaluation of muscle and lipid relaxation time mapping and comparison with standard techniques

ObjectiveTo implement magnetic resonance fingerprinting (MRF) on a permanent magnet 50 mT low-field system deployable as a future point-of-care (POC) unit and explore the quality of the parameter maps.Materials and methods3D MRF was implemented on a custom-built Halbach array using a slab-selective spoiled steady-state free precession sequence with 3D Cartesian readout. Undersampled scans were acquired with different MRF flip angle patterns and reconstructed using matrix completion and matched to the simulated dictionary, taking excitation profile and coil ringing into account. MRF relaxation times were compared to that of inversion recovery (IR) and multi-echo spin echo (MESE) experiments in phantom and in vivo. Furthermore, B0 inhomogeneities were encoded in the MRF sequence using an alternating TE pattern, and the estimated map was used to correct for image distortions in the MRF images using a model-based reconstruction.ResultsPhantom relaxation times measured with an optimized MRF sequence for low field were in better agreement with reference techniques than for a standard MRF sequence. In vivo muscle relaxation times measured with MRF were longer than those obtained with an IR sequence (T1: 182 ± 21.5 vs 168 ± 9.89 ms) and with an MESE sequence (T2: 69.8 ± 19.7 vs 46.1 ± 9.65 ms). In vivo lipid MRF relaxation times were also longer compared with IR (T1: 165 ± 15.1 ms vs 127 ± 8.28 ms) and with MESE (T2: 160 ± 15.0 ms vs 124 ± 4.27 ms). Integrated ΔB0 estimation and correction resulted in parameter maps with reduced distortions.DiscussionIt is possible to measure volumetric relaxation times with MRF at 2.5 × 2.5 × 3.0 mm3 resolution in a 13 min scan time on a 50 mT permanent magnet system. The measured MRF relaxation times are longer compared to those measured with reference techniques, especially for T2. This discrepancy can potentially be addressed by hardware, reconstruction and sequence design, but long-term reproducibility needs to be further improved.

Time-domain proton-detected local-field NMR for molecular structure determination in complex lipid membranes.

Proton-detected local-field (PDLF) NMR spectroscopy, using magic-angle spinning and dipolar recoupling, is presently the most powerful experimental technique for obtaining atomistic structural information from small molecules undergoing anisotropic motion. Common examples include peptides, drugs, or lipids in model membranes and molecules that form liquid crystals. The measurements on complex systems are however compromised by the larger number of transients required. Retaining sufficient spectral quality in the direct dimension requires that the indirect time-domain modulation becomes too short for yielding dipolar splittings in the frequency domain. In such cases, the dipolar couplings can be obtained by fitting the experimental data; however ideal models often fail to fit PDLF data properly due to effects of radiofrequency field (RF) spatial inhomogeneity. Here, we demonstrate that by accounting for RF spatial inhomogeneity in the modeling of R-symmetry-based PDLF NMR experiments, the fitting accuracy is improved, facilitating the analysis of the experimental data. In comparison to the analysis of dipolar splittings without any fitting procedure, the accurate modeling of PDLF measurements makes possible three important improvements: the use of shorter experiments that enable the investigation of samples with a higher level of complexity, the measurement of C-H bond order parameters with smaller magnitudes and of smaller variations of caused by perturbations of the system, and the determination of values with small differences from distinct sites having the same chemical shift. The increase in fitting accuracy is demonstrated by comparison with H NMR quadrupolar echo experiments on mixtures of deuterated and non-deuterated dimyristoylphosphatidylcholine (DMPC) and with 1-palmitoyl-2-oleoyl--glycero-3-phosphoethanolamine (POPE) membranes. Accurate modeling of PDLF NMR experiments is highly useful for investigating complex membrane systems. This is exemplified by application of the proposed fitting procedure for the characterization of membranes composed of a brain lipid extract with many distinct lipid types.

Correcting Coherent Errors by Random Operation on Actual Quantum Hardware

Characterizing and mitigating errors in current noisy intermediate-scale devices is important to improve the performance of the next generation of quantum hardware. To investigate the importance of the different noise mechanisms affecting quantum computation, we performed a full quantum process tomography of single qubits in a real quantum processor in which echo experiments are implemented. In addition to the sources of error already included in the standard models, the obtained results show the dominant role of coherent errors, which we practically corrected by inserting random single-qubit unitaries in the quantum circuit, significantly increasing the circuit length over which quantum computations on actual quantum hardware produce reliable results.

Fourier transform temporal diffusion spectroscopy

Temporal diffusion spectroscopy (TDS) currently uses the oscillating gradient spin echo (OGSE) experiment to measure the spectral density of translational velocity autocorrelation at single frequencies. Due to timing restrictions imposed by the transverse relaxation, the frequency selectivity and the sampling density of OGSE are limited, especially at low frequencies. We propose to overcome this problem by adopting the principles of Fourier transform spectroscopy. The new method of Fourier transform TDS (FTDS) uses two broadband gradient waveforms with different relative delays to make the spin echo attenuation sensitive to a broad range of diffusion frequencies with different harmonic modulations and calculates the spectrum by discrete Fourier transform. The method was validated by a measurement of diffusion spectra in highly restrictive tissues of a celery stalk and provided results consistent with OGSE, however, on a denser frequency grid.

Intrinsic stiffening and dynamic softening by cholesterol.

The stiffness of a lipid bilayer is the key mechanical constant for understanding membrane reshaping in the cell. Cholesterol, present in the plasma membrane at high levels, has ambiguous effects on stiffness that appears to depend strongly on the lipid matrix. Inferred from long length and time scale experiments (e.g., X-ray diffraction and GUV fluctuations) cholesterol has little effect on a simple di-oleoyl-phosphatidylcholine (DOPC) bilayer. Inferred from dynamic experiments limited to nanosecond timescales (e.g., neutron spin echo) DOPC bilayers appear stiffer. In a saturated chain matrix like DMPC, both x-ray and neutron spin echo experiments indicate stiffening.

Semi-Automatic Defect Distinction of PAUT for High Strength Steel Corner Structure

In this study, A GCN distinction network is proposed to identify the defect status of steel corner structures. In this defect determination method, the detected S-scan data is converted into A-scan by Doppler software to form a two-dimensional detection matrix, and the two dimensions are deflection angle stepping and sampling point on the acoustic distance respectively. GCN needs data node relations for GCN’s adjacent matrix, which concludes the shape of the sample and the reflection information and the structure of acoustic beam direction. The conventional inverse and threshold method are introduced in order to enhance classification performance. According to the node and the adjacency matrix relationship between nodes of affiliation and node sampling value automatically set the node label, The GCN model is constructed. Due to the characteristics of GCN, the beam length in the adjacent matrix cannot be changed again in the application test. Except for the detection model of Beamtool software, all other data processes and distinction are carried out automatically. In this study, the PAUT of low-alloy steel (30CrMnSi) was carried out by the PHASCAN II detector, to verify the effectiveness of the research method through natural wave and defect echo experiments which will be confused to distinguish.

Effect of rotation in NMR diffusion experiments on micron-sized particles: A generalized theoretical treatment

We have recently developed an analytical framework to interpret the results of pulsed field gradient (PFG) NMR experiments on solution samples of micron-sized amyloid fibrils [Angew. Chem. Int. Ed. 60 (2021) 15445–15451. https://doi.org/10.1002/anie.202102408]. Here we generalize this result by reporting a rigorous theoretical model of such experiments, implemented in a form of efficient computational scheme. In particular, the new treatment fully accounts for the anisotropy of fibrils’ translational diffusion and takes into consideration the finite length of the gradient pulses. The results hold not only for the historic spin-echo sequence, but also for the widely used stimulated echo experiment. We have found that fibrils’ rotation can attenuate the echo by a factor comparable with that of translation. However, contrary to some recent claims, the rotational mechanism cannot lead to an apparent fast-diffusion situation.

Ramsey envelope modulation in NV diamond magnetometry

Nitrogen-vacancy (NV) spin ensembles in diamond provide an advanced magnetic sensing platform, with applications in both the physical and life sciences. The development of isotopically engineered $^{15}$NV diamond offers advantages over naturally occurring $^{14}$NV for magnetometry, due to its simpler hyperfine structure. However, for sensing modalities requiring a bias magnetic field not aligned with the sensing NV axis, the absence of a quadrupole moment in the $^{15}$N nuclear spin leads to pronounced envelope modulation effects in time-dependent measurements of $^{15}$NV spin evolution. While such behavior in spin echo experiments are well studied, analogous effects in Ramsey measurements and the implications for magnetometry remain under-explored. Here, we derive the modulated $^{15}$NV Ramsey response to a misaligned bias field, using a simple vector description of the effective magnetic field on the nuclear spin. The predicted modulation properties are then compared to experimental results, revealing significant magnetic sensitivity loss if unaddressed. We demonstrate that double-quantum coherences of the NV $S=1$ electronic spin states dramatically suppress these envelope modulations, while additionally proving resilient to other parasitic effects such as strain heterogeneity and temperature shifts.

Signatures of electronic correlations and spin-susceptibility anisotropy in nuclear magnetic resonance

We present a methodology for probing the details of electronic susceptibility through minimally-invasive nuclear magnetic resonance techniques. Specifically, we classify electron-mediated long-range interactions in an ensemble of nuclear spins by revealing their effect on simple spin echo experiments. We find that pulse strength and applied field orientation dependence of these spin echo measurements resolves the spatial extent and anisotropy of electronic spin susceptibility. This work provides an alternate explanation to NMR results in superconducting and magnetically-ordered systems. The methodology has direct applications for sensing and characterizing emergent electronic phases.

From ECHo-1k to ECHo-100k:Optimization of High-Resolution Metallic Magnetic Calorimeters with Embedded 163Ho for Neutrino Mass Determination

The ECHo experiment aims at determining the effective electron neutrino mass by analyzing the endpoint of the 163Ho electron capture spectrum. High energy resolution detectors with a well-tailored detector response are the essential ingredient for the success of the ECHo experiment. Metallic magnetic calorimeter arrays enclosing 163Ho have been chosen for the ECHo experiment. The first MMC array, ECHo-1k, showed excellent performances with an average energy resolution of 5.5 eV FWHM @ 5.9 keV. Based on the results obtained with the ECHo-1k array, optimization studies have paved the way towards a new detector design for the next experimental phase, ECHo-100k. The ECHo-100k chip features an optimized single pixel design to improve the detector performance as well as an upgraded on-chip thermalization layout. The newly fabricated ECHo-100k detectors have been fully characterized at room temperature, at 4 K and at millikelvin temperature. The obtained results show that the ECHo-100k array achieved the expected performance with an average energy resolution of 3.5 eV FWHM @ 5.9 keV, fulfilling the requirements for the ECHo-100k experimental phase.

B(N) redor and B spin echo studies for structural charactreization of Si-B-N precursor ceramics

A Solid-state NMR spectroscopy is employed for the structural characterization oj precursorderived Si-B-C-N ceramics. Particular emphasis is given to the structural composition of the BNCx phase which plays a key role for the unusual high temperature stability of these materials. In the present work nB('5N) REDOR and B spin echo experiments are presented for two /SN enriched precursor systems, made from substituted polysilazanes and polvsilvlcarbodiimides. which provide interatomic boron-boron and boron-nitrogen distances. The obtained results are compatible with the presence of layered structures as reported for hexagonal boron nitride [h-BJ. The derived boron-nitrogen and boron-boron distances, however, are larger than in h-BN, reflecting some layer distortions. The boron-boron distances are found to decrease with increasing pyrolysis temperature, whereas the boron-nitrogen distances remain practically unaltered at elevated pyrolysis temperatures. On the basis of the present results it is concluded that intercalated BN.and sp2-carbon layers most likely constitute the BNCX. phase. The graphite-like carbon layers are assumed to create some internal pressure, which in turn is responsible for the observed interatomic distance increase in the BN layers. However, other scenarios, like the direct incorporation of small sp1-carbon domains into the BN-sheets, cannot be ruled out completely. Further work along this line appears to be necessary to develop a comprehensive structural model for the BNCxphase in such quarternarv ceramic systems.