Nuclear quadrupole interactions and charge localization in HgBa2CuO4 + δ with different oxygen content

Gippius, A. A.; Антипов, Е.В.; Hoffmann, W.; Lüders, Klaus

doi:10.1016/s0921-4534(97)00019-1

Cited by 39 publications

(28 citation statements)

References 30 publications

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“…where n hole is the number of holes per Cu(2) atom, and A and C are constants [24][25][26] . Although C is strongly material dependent, reflecting the difference in ν ion , A ≈ 20 − 30 MHz per hole for the Cu(2) atom is essentially material independent.…”

Section: Vortex Chargementioning

confidence: 99%

Charged vortices in high-temperature superconductors probed by NMR

2001

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We report a first experimental evidence that a vortex in the high temperature superconductors (HTSC) traps a finite electric charge from the high resolution measurements of the nuclear quadrupole frequencies. In slightly overdoped YBa2Cu3O7 the vortex is negatively charged by trapping electrons, while in underdoped YBa2Cu4O8 it is positively charged by expelling electrons. The sign of the trapped charge is opposite to the sign predicted by the conventional BCS theory. Moreover, in both materials, the deviation of the magnitude of the charge from the theory is also significant. These unexpected features can be attributed to the novel electronic structure of the vortex in HTSC.

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Section: Vortex Chargementioning

confidence: 99%

Charged vortices in high-temperature superconductors probed by NMR

2001

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“…[1][2][3] Nd 2−x Ce x CuO 4 (x=0, 0.13) single crystals. Based on these measurements and published data for the holedoped materials we develop the analysis in Ref.…”

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confidence: 99%

“…3 has the slope given by (2), a strong indication that the model describing the various parent compounds by varying n d and n p with material-independent 63 C c and 17 C σ is appropriate. In order to determine the absolute hole contents we need to determine these constants that are not uniquely defined by (3) and 63 ν 0 Q,c = 75.3 MHz, the intersect in Fig. 3.…”

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confidence: 99%

Distribution of electrons and holes in cuprate superconductors as determined from17OandCu63nuclear magnetic resonance

et al. 2014

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The distribution of electrons and holes in the CuO2 plane of the high-temperature superconducting cuprates is determined with nuclear magnetic resonance through the quadrupole splittings of 17 O and 63 Cu. Based on new data for single crystals of electron-doped Pr2−xCexCuO4(x=0, 0.05, 0.10, 0.15) as well as Nd2−xCexCuO4 (x=0, 0.13) the changes in hole contents n d of Cu 3d(x 2 − y 2 ) and np of O 2pσ orbitals are determined and they account for the stoichiometrically doped charges, similar to hole-doped La2−xSrxCuO4. It emerges that while n d + 2np = 1 in all parent materials as expected, n d and np vary substantially between different groups of materials. Doping holes increases predominantly np, but also n d . To the contrary, doping electrons predominantly decreases n d and only slightly np. However, np for the electron doped systems is higher than that in hole doped La1.85Sr0.15CuO4. Cuprates with the highest maximum Tcs appear to have a comparably low n d while, at the same time, np is very high. The rather high oxygen hole content of the Pr2CuO4 and Nd2CuO4 with the low n d seems to make them ideal candidates for hole doping to obtain the highest Tc. The high-temperature superconducting cuprates (HTSCs) emerge from insulating antiferromagnetic parent materials, the essential unit of which is the CuO 2 plane. It is formed, in first approximation, by Cu 2+ (3d 9 ) and O 2− (2p 6 ), with the half-filled Cu 3d(x 2 − y 2 ) orbital hybridized with four O 2p σ orbitals, so that a near square planar arrangement of Cu and O follows. Charge neutrality is provided by layers between CuO 2 planes, the chemistry of which can be varied widely. By changing the average charge state of the layers, e.g., by doping them, electrons are added or removed from the CuO 2 plane. These additional electrons or holes destroy the Cu-based antiferromagnetism. Above a certain doping level superconductivity can emerge with a maximum critical transition temperature T c at optimal average doping, and it decreases nearly parabolically as the doping departs from the optimal value. The highest T c 's vary widely among different materials, and it is not quite clear which material parameters affect this behavior. Therefore, the knowledge of the microscopic distribution of charges in the CuO 2 plane is of great interest for a better understanding of the doping process.A local probe like nuclear magnetic resonance (NMR) can yield vital information about the doping process since a change in the hole or electron content in the Cu 3d(x 2 − y 2 ) or O 2p σ orbitals changes the electric field gradients (EFGs) experienced by the 63,65 Cu (I = 3 2) and 17 O (I = 5 2) nuclei through the electric quadrupole interaction that splits the nuclear resonances for Cu and O into 2I lines in a high magnetic field. Their frequencies are given by ν n = ν 0 ± nν Q : the central line (n = 0) is in leading order unaffected by the quadrupole interaction that causes an angular dependent quadrupole splitting ν Q for the 2I − 1 satellite transitions (n = 1 for Cu and n = 1, ...

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“…In this context, magnetic fields at the apical oxygen site, Fig.1(a) 89 Y is in a symmetry position which is insensitive to orbital current ordering and neutron data is not available in these materials for direct comparison. We report here our investigation of local fields in Hg1201 with 17 O NMR for which the apical oxygen is sensitive to orbital currents and polarized neutron scattering show evidence for magnetic ordering.Until recently, NMR results for Hg1201 have been constrained to c-axis magnetically aligned powdered samples, [22][23][24][25] which are more easily annealed and have a large NMR signal. However, these powder samples are disordered in the ab-plane and they can have a larger spectral linewidth due to imperfect alignment.…”

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confidence: 99%

Absence of Static Loop-Current Magnetism at the Apical Oxygen Site inHgBa2CuO4+δfrom NMR

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Lee

et al. 2013

Phys. Rev. Lett.

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The simple structure of HgBa2CuO 4+δ (Hg1201) is ideal among cuprates for study of the pseudogap phase as a broken symmetry state. We have performed 17 O nuclear magnetic resonance (NMR) on an underdoped Hg1201 crystal with transition temperature of 74 K to look for circulating orbital currents proposed theoretically and inferred from neutron scattering. The narrow spectra preclude static local fields in the pseudogap phase at the apical site, suggesting that the moments observed with neutrons are fluctuating. The NMR frequency shifts are consistent with a dipolar field from the Cu +2 site. [14] show the appearance of broken time reversal symmetry that correlates with the onset of the pseudogap phase with a magnetic moment tilted away from the crystalline c-axis. A muon spin relaxation (µSR) experiment in zero field was unable to detect this magnetism [15] although screening effects may account for muon insensitivity. [16] To account for neutron data, extensions of 2D orbital currents to 3D models have been proposed which include the apical oxygen[17] as well as a quantum mechanical calculation [18] which has an out-of-plane component with a tilted local field. In this context, magnetic fields at the apical oxygen site, Fig.1(a) 89 Y is in a symmetry position which is insensitive to orbital current ordering and neutron data is not available in these materials for direct comparison. We report here our investigation of local fields in Hg1201 with 17 O NMR for which the apical oxygen is sensitive to orbital currents and polarized neutron scattering show evidence for magnetic ordering.Until recently, NMR results for Hg1201 have been constrained to c-axis magnetically aligned powdered samples, [22][23][24][25] which are more easily annealed and have a large NMR signal. However, these powder samples are disordered in the ab-plane and they can have a larger spectral linewidth due to imperfect alignment. In order to investigate possible effects of orbital currents, high arXiv:1304.6415v1 [cond-mat.supr-con]

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Nuclear quadrupole interactions and charge localization in HgBa2CuO4 + δ with different oxygen content

Cited by 39 publications

References 30 publications

Charged vortices in high-temperature superconductors probed by NMR

Charged vortices in high-temperature superconductors probed by NMR

Distribution of electrons and holes in cuprate superconductors as determined from17OandCu63nuclear magnetic resonance

Absence of Static Loop-Current Magnetism at the Apical Oxygen Site inHgBa2CuO4+δfrom NMR

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