63Cu Nuclear Magnetic Resonance Research Articles

Charge Order and Fluctuations in Bi2Sr2−xLaxCuO6+δRevealed by63,65Cu-Nuclear Magnetic Resonance

The discovery of a magnetic-field-induced charge-density-wave (CDW) order in the pseudogap state via nuclear magnetic resonance (NMR) studies has highlighted the importance of “charge” in the physics of high transition-temperature (Tc) superconductivity in copper oxides (cuprates). Herein, after briefly reviewing the progress achieved in the last few years, we report new results of 63,65Cu-NMR measurements on the CDW order and its fluctuation in the single-layered cuprate Bi2Sr2−xLaxCuO6+δ. The NMR spectrum under both in- and out-of-plane magnetic fields above H = 10 T indicates that the CDW replaces the antiferromagnetic order before superconductivity appears, but disappears before superconductivity is optimized. We found that the CDW onset temperature TCDW scales with the pseudogap temperature T*. Comparison between 63Cu and 65Cu NMR indicates that the spin–lattice relaxation process is dominated by charge fluctuations in the doping regions where the CDW appears as well as at the pseudogap end point (T* = 0). These results suggest that charge orders and fluctuations exist in multiple doping regions and over a quite wide temperature range.

Moissanite anvil cell single crystal NMR at pressures of up to 4.4 GPa.

High-pressure anvil cell nuclear magnetic resonance (NMR) studies of single crystals are challenging, but they can offer much insight into material properties. A microcoil inside the high-pressure region that encloses the crystal offers a good signal-to-noise ratio, but special care has to be taken to warrant hydrostatic conditions or to avoid rupture of the crystal or coil. By introducing precise monitoring of the height and diameter of the pressurized sample chamber, this can be ensured, and the data reveal the behavior of the sample chamber under pressure. While its total volume is given by the compression of the enclosed pressure transmitting fluid, the aspect ratio of the cylindrical chamber changes considerably. 63Cu and 17O NMR of two differently doped single crystals of YBa2Cu3O7-δ at pressures of up to about 4.4GPa show the function of the cell, and orientation dependent spectra prove the soundness of the arrangement.

Сверхтонкие взаимодействия в узлах меди антиферромагнитных соединений, аналогов сверхпроводящих металлооксидов меди

Emission Mössbauer spectra of 61Cu(61Ni) in dielectric metal oxides of divalent copper Ca1−xSrxCuO2, Ca2CuO2Cl2, Sr2CuO2Cl2, YBa2Cu3O7−x, La2−xSrxCuO4 and Nd2−xCexCuO4 correspond to the combined quadrupole and Zeeman interaction of 61Ni nuclei with local fields at the sites of copper. For the superconducting metal oxides, on the other hand, spectra correspond to the interaction of the quadrupole moment of 61Ni nuclei with the electric field gradient. The both groups of metal oxides show linear dependences of the quadrupole interaction constants on the calculated values of the principal components of the lattice electric field gradient tensor at the copper sites for 61Ni nuclei (emission 61Cu(61Ni) Mössbauer spectroscopy data) as well as for 63Cu nuclei (63Cu nuclear magnetic resonance data). This fact is explained by invariable values of the valence component of electric field gradient for both 61Ni2+ and 63Cu2+ probes in all divalent copper metal oxides under investigation.

Properties of the Electronic Fluid of Superconducting Cuprates from 63Cu NMR Shift and Relaxation

Nuclear magnetic resonance (NMR) provides local, bulk information about the electronic properties of materials, and it has been influential for theories of high-temperature superconducting cuprates. NMR reported 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, i.e., they are only affected by Tc not the pseudogap. 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(x2 − y2) 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.

Features of 63,65Cu NMR Spectra in the Local Field of Samples of CuFeS2 Semiconductor Mineral from Oceanic Sulfide Deposits

The results of studying natural samples of CuFeS2 chalcopyrite mineral from hydrothermal ore manifestations of island arcs of the Pacific Ocean by 63Cu nuclear magnetic resonance (63Cu NMR) in a local field at room temperature are presented. The asymmetric shape of the detected resonance lines in the 63Cu NMR spectrum indicates the presence of at least two overlapping lines. The presence of two overlapping central components can be a consequence of the occurrence of regions with different types of structural distortion near the resonant nuclei. These results show that the pulsed 63Cu NMR method can be an effective method for studying the physical properties of deep-sea polymetallic sulfides of the global ocean.

Особенности спектров ЯМР -=SUP=-63,65-=/SUP=-Cu в локальном поле образцов полупроводникового минерала CuFeS-=SUB=-2-=/SUB=- из сульфидных месторождений океана

AbstractThe results of studying natural samples of CuFeS_2 chalcopyrite mineral from hydrothermal ore manifestations of island arcs of the Pacific Ocean by ^63Cu nuclear magnetic resonance (^63Cu NMR) in a local field at room temperature are presented. The asymmetric shape of the detected resonance lines in the ^63Cu NMR spectrum indicates the presence of at least two overlapping lines. The presence of two overlapping central components can be a consequence of the occurrence of regions with different types of structural distortion near the resonant nuclei. These results show that the pulsed ^63Cu NMR method can be an effective method for studying the physical properties of deep-sea polymetallic sulfides of the global ocean.

Charge-density-wave order takes over antiferromagnetism in Bi2Sr2\u2212xLaxCuO6 superconductors

Superconductivity appears in the cuprates when a spin order is destroyed, while the role of charge is less known. Recently, charge density wave (CDW) was found below the superconducting dome in YBa2Cu3Oy when a high magnetic field is applied perpendicular to the CuO2 plane, which was suggested to arise from incipient CDW in the vortex cores that becomes overlapped. Here by 63Cu-nuclear magnetic resonance, we report the discovery of CDW induced by an in-plane field, setting in above the dome in single-layered Bi2Sr2−xLaxCuO6. The onset temperature TCDW takes over the antiferromagnetic order temperature TN beyond a critical doping level at which superconductivity starts to emerge, and scales with the pseudogap temperature T*. These results provide important insights into the relationship between spin order, CDW and the pseudogap, and their connections to high-temperature superconductivity.

Copper dynamics and structural-transformation in noble metal chalcogenides CuAgS probed by 63Cu NMR

Atomic-scale dynamics of a representative noble metal chalcogenide superionic conductor, stromeyerite (CuAgS), were examined by nuclear magnetic resonance (NMR) spectroscopy at various temperatures. Motional narrowing of 63Cu NMR line width was found in its cubic phase, demonstrating copper ions start diffusing via a hopping process. Moreover, the absence of 63Cu NMR signal in its orthorhombic or hexagonal phases was discussed, which could be well explained by copper ordering and reduced local symmetry at copper sites. The above NMR results are relevant for understanding its electron-crystal phonon-liquid behaviors and transient structure-transformation, which are associated with extremely low thermal conductivities and abnormal change of thermal power during superionic phase transition in this material.

Investigations of CuFeS2 semiconductor mineral from ocean rift hydrothermal vent fields by Cu NMR in a local field

The results of investigating natural samples of chalcopyrite mineral CuFeS2 from massive oceanic sulfide ores of the Mid-Atlantic ridge by the 63Cu nuclear magnetic resonance (NMR 63Cu) in a local field at room temperature are presented. The significant width of the resonance lines found in the 63Cu NMR spectrum directly testifies to a wide distribution of local magnetic and electric fields in the investigated chalcopyrite samples. This distribution can be the consequence of an appreciable deviation of the structure of the investigated chalcopyrite samples from the stoichiometric one. The obtained results show that the pulsed 63Cu NMR can be an efficient method for studying the physical properties of deep-water polymetallic sulfides of the World Ocean.

Physical properties and magnetic structure of the intermetallicCeCuBi2compound

In this work, we combined magnetization, pressure dependent electrical resistivity, heat-capacity, 63Cu Nuclear Magnetic Resonance (NMR) and X-ray resonant magnetic scattering experiments to investigate the physical properties of the intermetallic CeCuBi2 compound. Our single crystals show an antiferromagnetic ordering at TN ~ 16 K and the magnetic properties indicate that this compound is an Ising antiferromagnet. In particular, the low temperature magnetization data revealed a spin-flop transition at T = 5 K when magnetic fields about 5.5 T are applied along the c-axis. Moreover, the X-ray magnetic diffraction data below TN revealed a commensurate antiferromagnetic structure with propagation wavevector (0 0 1/2) with the Ce^3+ moments oriented along the c-axis. Furthermore, our heat capacity, pressure dependent resistivity and temperature dependent 63Cu NMR data suggest that CeCuBi2 exhibits a weak heavy fermion behavior with strongly localized Ce^3+ 4f electrons. We thus discuss a scenario taking into account the anisotropic magnetic interaction between the Ce^3+ ions along with the tetragonal crystalline electric field effects in CeCuBi2.

Bond strength dependent superionic phase transformation in the solid solution series Cu2ZnGeSe4−xSx

Recently, copper selenides have shown to be promising thermoelectric materials due to their possible superionic character resulting from mobile copper cations. Inspired by this recent development in the class of quaternary copper selenides we have focused on the structure-to-property relationships in the solid solution series Cu2ZnGeSe4−xSx. The material exhibits an insulator-to-metal transition at higher temperatures, with a transition temperature dependent on the sulfur content. However, the lattice parameters show linear thermal expansion at elevated temperatures only and therefore no indication of a structural phase transformation. 63Cu nuclear magnetic resonance shows clear indications of Cu located on at least two distinct sites, which eventually merge into one (apparent) site above the phase transformation. In this manuscript the temperature dependent lattice parameters and electronic properties of the solid solution Cu2ZnGeSe4−xSx are reported in combination with 63Cu NMR, and an attempt will be made to relate the nature of the electronic phase transformation to a superionic phase transformation and a changing covalent character of the lattice upon anion substitution in this class of materials.

Charge Inhomogeneity in Electron-Doped Pr1.85Ce0.15CuO4 Determined with 63Cu NMR

Nuclear Magnetic Resonance (NMR) of Cu and O has been applied successfully to probe locally the charge distribution in the CuO2 plane of the hole-doped cuprates. However, for the electron-doped systems, only insufficient Cu NMR data are available. Here, with a set of new 63Cu NMR experiments including double-resonance experiments, we examine the quadrupole interaction for a single crystal of Pr1.85Ce0.15CuO4. From the data, we deduce that the doped electrons mainly enter the Cu \(3\mathrm{d}_{x^{2}-y^{2}}\) orbital resulting in an almost vanishing electric field gradient. In addition, we observe a substantial variation across the CuO2 plane that, however, remains largely axially symmetric. We estimate 13 % doped carriers at 15 % nominal doping with a charge density variation of at least 4 % for this optimally doped sample.

A Comparative Nuclear Magnetic Resonance Study of the Solvation of CuClO4 in Binary Mixtures of Acetonitrile with Pyridine and Picolines at 298K

63Cu nuclear magnetic resonance (NMR) and viscosity studies of 0:064M CuClO4 solutions have been reported in binary mixtures of acetonitrile (AN) with pyridine (Py) and 2, 3, and 4-picolines (2,3,4-Pic) at 298 K using a Bruker 500 MHz NMR spectrometer and an Ubbelohde viscometer, respectively. Chemical shift d and linewidth D for the 63Cu signals have been recorded referenced to a 0:064M CuClO4 solution in anhydrous AN. The copper quadrupole coupling constants (e 2 Qq=h) have been calculated in all cases. The variation of the d and e 2 Qq=h values as a function of mol fraction of the co-solvent show that all these bases interact with Cu+ more strongly than AN. They replace AN from the Cu+ complexed with AN in the form [Cu(AN)4]+ and form a mixed complex of the type [Cu(AN)4-x(S)x]+ (x=1 - 4) where S stands for the base. At relatively high mole fraction of the co-solvents, the mixed solvated complex gradually changes to a more symmetrical complex of the type [Cu(S)4]+ which remains stable in the solution. The solvating effect of 2-Pic and 4-Pic is observed to be stronger than that of Py and 3-Pic.

Temperature calibration for high-temperature MAS NMR to 913 K: 63Cu MAS NMR of CuBr and CuI, and 23Na MAS NMR of NaNbO 3

The solid-state phase transitions of CuBr, CuI and NaNbO 3 can be readily observed using 63Cu and 23Na high-temperature magic-angle spinning nuclear magnetic resonance spectroscopy. Temperature has large, linear effects on the peak maximum of 63Cu in each solid phase of CuBr and CuI, and there is large jump in shift across each phase transition. The 23Na MAS NMR peak intensities and the line widths in NaNbO 3 also clearly show its high-temperature transition to the cubic phase. These data can be used to calibrate high-temperature MAS NMR probes up to 913 K, which is two hundred degrees higher than the commonly-used temperature calibration based on the chemical shift of 207Pb in Pb(NO 3) 2.

63Cu nuclear magneticresonance study of Pr1.85Ce0.15Cu1 − xNixO4: Ni-induced spin density oscillation and modification of the low energy spin fluctuations

We report the results from a 63Cu nuclear magnetic resonance (NMR) study of the electron-doped high temperature superconducting cuprate(HTSC) Pr1.85Ce0.15Cu1 − xNixO4. We find that Ni induces a magnetic broadening of the 63Cu NMR spectra that can be interpreted in terms of an induced spindensity oscillation about the Ni site, similar to that reported from 63Cu NMR measurements on the hole-doped HTSCs when Zn is partially substitutedfor Cu. There is also an additional temperature-dependent contribution to the 63Cu spin–lattice relaxation rate that can be interpreted in terms of an Ni-inducedmodification of the low energy spin fluctuations. Furthermore, the spin fluctuations areintrinsically spatially inhomogeneous and additional inhomogeneities are induced by Ni.

63Cu NMR spectra, magnetic susceptibility, and transmission electron microscopy of the rapidly quenched alloy Ti50Ni25Cu25

Methods of transmission and scanning electron microscopy and nuclear magnetic resonance (NMR) at 63Cu nuclei, as well as measurements of the static magnetic susceptibility χ(T) have been used to study a shape-memory alloy (SMA) Ti50Ni25Cu25, which experiences a thermoelastic martensite transformation. The alloy was obtained from an amorphous ribbon in a bimodal nano- and submicrocrystalline state via a crystallization annealing for 1 h at 770 K with a subsequent quenching to room-temperature water. The resultant B2 austenite is characterized by a fine structure of the 63Cu NMR spectra, which is connected with the different distribution of 63Cu atoms on the second coordination shell. The evolution of the shape of the spectra with decreasing temperature reveals a structural transition B2 → B19. In addition, the 63Cu NMR spectra, just as the transmission electron microscopy, indicate the presence of phase separation in the alloy, with the precipitation of a TiCu (B11) phase. The temperature dependence of the static magnetic susceptibility χ(T) also indicates the occurrence of a structural transition and has a hysteretic nature of “stepped” type. The discovered stepped nature of the χ(T) dependence is explained by the bimodal size distribution of grains of the B2 phase due to the size effect of the martensitic transformation.

Charge order and low frequency spin dynamics in lanthanum cuprates revealed by Nuclear Magnetic Resonance

We report detailed 17O, 139La, and 63Cu Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) measurements in a stripe ordered La1.875Ba0.125CuO4 single crystal and in oriented powder samples of La1.8-xEu0.2SrxCuO4. We observe a partial wipeout of the 17O NMR intensity and a simultaneous drop of the 17O electric field gradient (EFG) at low temperatures where the spin stripe order sets in. In contrast, the 63Cu intensity is completely wiped out at the same temperature. The drop of the 17O quadrupole frequency is compatible with a charge stripe order. The 17O spin lattice relaxation rate shows a peak similar to that of the 139La, which is of magnetic origin. This peak is doping dependent and is maximal at x ~ 1/8.

27Al and 63Cu NMR studies on intermetallic Kondo compound CeCu 3Al 2

Detailed 27Al and 63Cu nuclear magnetic resonance (NMR) experiments have been performed in between 4.5 and 295 K on a polycrystalline sample of CeCu 3Al 2 which has a Kondo temperature ∼ 11 K . The NMR spectral features and Knight shift measurements show that in this compound, Cu occupy both c and g lattice sites, while Al occupy only the g sites. From the temperature dependence of Knight shift ( K), the hyperfine fields for 63Cu and 27Al at the g sites have been estimated as 2.02(5) and 1.67 ( 5 ) kOe / μ B , respectively, and that for 63Cu at c sites as − 3.83 ( 5 ) kOe / μ B . Nuclear spin-lattice relaxation time ( T 1) measurements indicate that though the relaxation process is governed by fluctuations of magnetic interaction, nuclear quadrupolar interaction also has a significant contribution, especially towards relaxation of 63Cu in both c and g sites. For 27Al, K and T 1 have yielded the effective 4f-spin correlation rate 1 / τ 4 f . The behavior of its temperature dependence indicates that at low temperatures in CeCu 3Al 2, the valence state of cerium might not be stable.

77Se and 63Cu NMR studies of the electronic correlations inCuxTiSe2 (x = 0.05, 0.07)

We report a 77Se and 63Cu nuclear magnetic resonance (NMR) investigation on the charge-density-wave (CDW) superconductorCuxTiSe2 (x = 0.05 and0.07). At high magnetic fields where superconductivity is suppressed, the temperature dependence of 77Se and 63Cu spin–lattice relaxationrates 1/T1 follow a linearrelation. The slope of 77Se 1/T1 versus T increases with the Cu doping. This can be described by a modified Korringa relation whichsuggests the significance of electronic correlations and the Se 4p- and Ti 3d-bandcontribution to the density of states at the Fermi level in the studied compounds.

Structural investigation of non-stoichiometric CuInS2 by 63Cu and 115In nuclear magnetic resonance

Results of studies of non-stoichiometric CuInS2 semiconductor by 63Cu and 115In nuclear magnetic resonance are presented. It was established that deviation of the composition from stoichiometry causes a quadrupolebroadened region of the NMR spectrum to change most. In this case a central peak whose shape is governed by the chemical shift anisotropy remains unaffected. NMR spectra reveal two types of structural distortions in the nearest surroundings of the In atoms.