Labeling in diffusion measurements by pulsed field gradient (PFG) NMR is based on the observation of the phase of nuclear spins acquired in a constant magnetic field with purposefully superimposed field gradients. This labeling does in no way affect microdynamics and provides information about the probability distribution of molecular displacements as a function of time. An introduction of the measuring principle is followed by a detailed description of the ranges of measurements and their limitation. Particular emphasis is given to an explanation of possible pitfalls in the measurements and the ways to circumvent them. Showcases presented for illustrating the wealth of information provided by PFG NMR include a survey on the various patterns of concentration dependence of intra-particle diffusion and examples of transport inhibition by additional transport resistances within the nanoporous particles and on their external surface. The latter information is attained by combination with the outcome of tracer exchange experiments, which are shown to become possible via a special formalism of PFG NMR data analysis. Further evidence provided by PFG NMR concerns diffusion enhancement in pore hierarchies, diffusion anisotropy and the impact of diffusion on chemical conversion in porous catalysts. A compilation of the specifics of PFG NMR and of the parallels with other measurement techniques concludes the paper.

Planar oxygen nuclear magnetic resonance (NMR) relaxation and shift data from all cuprate superconductors available in the literature are analyzed. They reveal a temperature-independent pseudogap at the Fermi surface, which increases with decreasing doping in family-specific ways, i.e., for some materials, the pseudogap is substantial at optimal doping while for others it is nearly closed at optimal doping. The states above the pseudogap, or in its absence are similar for all cuprates and doping levels, and Fermi liquid-like. If the pseudogap is assumed exponential it can be as large as about 1500 K for the most underdoped systems, relating it to the exchange coupling. The pseudogap can vary substantially throughout a material, being the cause of cuprate inhomogeneity in terms of charge and spin, so consequences for the NMR analyses are discussed. This pseudogap appears to be in agreement with the specific heat data measured for the YBaCuO family of materials, long ago. Nuclear relaxation and shift show deviations from this scenario near Tc, possibly due to other in-gap states.

Chronology assumes a central role in the process of historical and archaeological reconstruction by allowing us to time the change and development of human societies. Dating provides a framework for linking individual events together. It is the backbone for historical narratives, and connections between environmental and archaeological records on a global scale. However, until today, establishing a reliable chronology for ancient human societies and civilizations using pottery has remained one of the most contested topics of scientific discourse. Although the field of chronology has been revolutionized by modern historical and archaeological critical methods, through assessing historical sources and material

Nuclear magnetic resonance (NMR) provides local, bulk information about the electronic properties of materials, and it has been influential for theory of high-temperature superconducting cuprates. Importantly, NMR found early that nuclear relaxation is much faster than what one expects from coupling to fermionic excitations above the critical temperature for superconductivity (Tc), i.e. what one estimates from the Knight shift with the Korringa law. As a consequence, special electronic spin fluctuations have been invoked. Here, based on literature relaxation data it is shown that the electronic excitations, to which the nuclei couple with a material and doping dependent anisotropy, are rather ubiquitous and Fermi liquid-like. A suppressed NMR spin shift rather than an enhanced relaxation leads to the failure of the Korringa law for most materials. Shift and relaxation below Tc support the view of suppressed shifts, as well. A simple model of two coupled electronic spin components, one with 3d(x 2 −y 2 ) orbital symmetry and the other with an isotropic s-like interaction can explain the data. The coupling between the two components is found to be negative, and it must be related to the pseudogap behavior of the cuprates. We can also explain the negative shift conundrum and the long-standing orbital shift discrepancy for NMR in the cuprates.

Monitoring the recombination of OH groups in a ceramic sample after firing, also known as rehydroxylation (RHX), was proposed as a way to determine the time elapsed since the firing of a ceramic material, thus providing archeologists with the only up-to-date known method for determining the age of fired ceramics directly. A nuclear magnetic resonance (NMR) study was performed in order to understand the RHX dating of ceramic materials in archeology. We perform MAS NMR investigations on four pure clay minerals and one mixed ceramic. We point out a large discrepancy between NMR measurements and TG in the obtained total concentration of hydrogen. We are able to differentiate and investigate the dynamics (by monitoring H/D exchange) of the three types of hydrogen species present in the samples: T0 (physisorbed), T1 (interlayer), and T2 (chemisorbed) water. We use H/D tracer exchange to monitor the mobility of hydrogen species and obtain the exchange time constants of T2 water, which is in the order of a few to 100 days. Interestingly, we find that H/D exchange time constants do not significantly depend on temperature. The slow exchange times of T2 water, in the order of days, can be compared with the diffusion time scales of T1 water (in the order of 100 s) obtained with tracer desorption and with T0 water (order of 100 ms) obtained by PFG MAS NMR measurements.

Nuclear relaxation is an important thermodynamic probe of electronic excitations, in particular in conducting and superconducting systems. Here, an empirical phenomenology based on all available literature data for planar Cu in hole-doped cuprates is developed. It is found that most of the seemingly different relaxation rates among the systems are due to a temperature independent anisotropy that affects the mostly measured 1/T 1 , the rate with an external magnetic field along the crystal c-axis, while 1/T 1⊥ is largely independent on doping and material above the critical temperature of superconductivity (Tc). This includes very strongly overdoped systems that show Fermi liquid behavior and obey the Korringa law. Below Tc the relaxation rates are similar, as well, if plotted against the reduced temperature T /Tc. Thus, planar Cu nuclear relaxation is governed by a simple, dominant mechanism that couples the nuclei with varying anisotropy to a rather ubiquitous bath of electronic excitations that appear Fermi liquid-like irrespective of doping and family. In particular, there is no significant enhancement of the relaxation due to electronic spin fluctuations, different from earlier conclusions. Only the La2−xSrxCuO4 family appears to be an outlier as additional relaxation is present, however, the anisotropy remains temperature independent. Also systems with very low doping levels, for which there is a lack of data, may behave differently.

Very recently, there has been significant progress with establishing a common phenomenology of the superconducting cuprates in terms of nuclear magnetic resonance (NMR) shift and relaxation. Different from the old interpretation, it was shown that the shifts demand two coupled spin components with different temperature dependencies. One spin component couples isotropically to the planar Cu nucleus and is likely to reside at planar O, while the other, anisotropic component has its origin in the planar copper 3d(x 2 − y 2 ) orbital. Nuclear relaxation, on the other hand, was found to be rather ubiquitous and Fermi liquid-like for planar Cu, i.e., it is independent of doping and material, apart from the sudden drop at the superconducting transition temperature, Tc. However, there is a doping and material dependent anisotropy that is independent on temperature, above and below Tc. Here we present a slightly different analysis of the shifts that fits all planar Cu shift data. In addition we are able to derive a simple model that explains nuclear relaxation based on these two spin components. In particular, the only outlier so far, La2−xSrxCuO4, can be understood, as well. While this concerns predominantly planar Cu, it is argued that the two component model should fit all cuprate shift and relaxation data.March 25, 2020 ⊥ arXiv:2002.09903v2 [cond-mat.supr-con]

Nuclear magnetic resonance (NMR) is a fundamental bulk probe that provides key information about the electronic properties of materials. Very recently, the analysis of all available planar copper shift as well as relaxation data proved that while the shifts cannot be understood in terms of a single temperature-dependent spin component, relaxation can be explained with one dominating Fermi liquid-like component, without enhanced electronic spin fluctuations. For the shifts, a doping-dependent isotropic term as well as doping-independent anisotropic term became obvious. Here, we focus on planar [Formula: see text]O NMR shifts and quadrupole splittings. Surprisingly, we find that they demand, independently, a similar two-component scenario and confirm most of the previous conclusions concerning the properties of the spin components, in particular that a negative spin polarization survives in the superconducting state. This should have consequences for the pairing scenario.